Out of darkness and mist emerges a ghostly disembodied arm, marked by strange, illegible shapes and letters (Fig. 2.1). At first glance, it recalls the photographing of spirits more than medical subjects. Is this photographed forearm the product of a medical experiment gone wrong, or one its researcher got right?

2.1 ‘Finsen’s forearm, the day after its exposure for 20 minutes … by irradiation from a carbon arc [light].’

In Axel Reyn, ‘Histoire de l’actinothérapie’, in Charles Brody (ed.), Traité d’hélio- et d’actinologie (Paris: Maloine, 1938), vol. I, p. 41. Author’s collection.

Figure 2.1 is an odd and eerie photograph. It dates to c. 1893, now lost and only existing through poor reproductions. It represents the irradiated forearm of Dr Niels Finsen, the Danish researcher, Nobel laureate, and inventor of phototherapy. While not British, this photograph was reproduced and discussed by light-therapy practitioners internationally, and it provides a point of origin for the British images I analyse in this chapter. From its amateurish quality, especially those misty areas that are likely the result of clumsy ‘fixing’ during the development process, one might simply describe it as a bad photograph. Its illegibility, however, is of the utmost significance. The successes and failures of photography, as a light technology, to represent light therapy’s methods, effects, and values are paramount to the book’s central argument: from its inception light therapy was, and remains, an unstable, varied, and confounding medical practice.

Figure 2.1 presents, to my knowledge, the earliest image of modern light therapy or ‘scientific light treatment’, representing a rarely depicted but crucial component: the solar erythema (‘sunburn’).³ Shifting and shifty, physicians’ attitudes towards solar erythema as simultaneously dangerous and desirable persist throughout light therapy’s history. Historically, ‘sunburn’ was variously defined as erythema caloricum (heat erythema), photoelectricum (the electric effects of light), dermatitis solaris (dermatitis due to the sun), eczema solare (eczema due to the sun), as well as erythema solare (inflammation due to the sun).⁴ Such confusion centred on understandings of inflammation (erythema) resulting from the sun’s light as distinct from its heat. As early as 1858, the famous French neurologist Dr Jean-Martin Charcot suggested that solar erythema was generated by the blue, violet, and ultraviolet end of the spectrum, not by the infrared and red (heat) rays.⁵ Despite this differentiation becoming commonly understood by the 1890s, practitioners were still at pains to spell out the differences between these kinds of ‘burns’ well into the 1920s, distinguishing them not according to any visual referents but rather to timing: a heat erythema manifested immediately; a light (solar) erythema was characterised by its latent appearance.⁶

Yet, as an acute inflammation of the skin, accompanied by redness, pain, a burning or stinging sensation, and sometimes blisters, the word ‘sunburn’ persisted throughout the nineteenth and twentieth centuries, and it persists today. For the sake of clarity I employ the term ‘solar erythema’ to mean the reddening of the skin in response to actinic light, particularly ultraviolet light, as was its typical meaning by light-therapy practitioners. However, this is not to ignore or let slip an awareness of the unstable, multivalent meanings of the word ‘sunburn’. They heavily inform my reading of the primary literature and visual material on the benefits and risks of ‘dosing’ light. In this chapter, I argue that such instability of definition in the texts, analogous to the illegibility and paucity of the images, can be a productive rather than limiting way into an analysis of light therapy’s history. I want us to remain aware throughout the chapter of the powerful status of images as ‘evidence’ or ‘documentation’, particularly when it comes to evidencing medical practices and success.

In Section I of this chapter, I show that, as the initial visible sign of the skin’s reaction to light treatment, the solar erythema was closely scrutinised and discussed by practitioners of both natural sunlight therapy (heliotherapy) and artificial light therapy (phototherapy). Patients’ photosensitivities were monitored closely to gauge whether the treatment would be successful or not, but the degree and kind of reaction produced to determine ‘success’ varied enormously among practitioners, in Britain and abroad. As I discuss in Chapter 5, pigmentation (‘suntan’) had a related role to play, many practitioners desiring greatly to see bronzed flesh as a marker of healing over red, blistered, and peeling skin. But others did not. Some of Britain’s leading practitioners, including Sir Leonard Hill and his colleague Dr Albert Eidinow of the MRC’s NIMR, actively sought red flesh, not brown, as the sign of the cure under way.

The relationship between erythema and pigmentation – as distinct physiological phenomena, as sequential processes in a single reaction, or as one and the same thing – consequently emerges as extraordinarily complicated within the primary literature and imagery.⁷ Black-and-white photography, the major medium of light therapy’s visual culture, epitomises the ambiguity when we consider how difficult it is to differentiate between the hues of erythema (red) and pigmentation (brown) when presented in tones of grey. Take the photograph of Finsen’s forearm, for example (Fig. 2.1): our only clue as to whether this is a representation of erythema or of pigmentation is in the written description by Finsen’s successor, Dr Axel Reyn, who explained that the photograph was taken the day after the arm was exposed to a carbon arc lamp, and thus too soon for pigmentation to have developed. This chapter concentrates on the many textual and few visual representations of solar erythema, of what it was, how it functioned in the therapeutic process, and its contentious role in the development and legitimisation of light therapy.

From modern light therapy’s inception in the 1890s to its widespread use by the 1930s, the solar erythema took a leading role in practitioners’ attempts to present the therapy as scientifically standardised and systematic – or, conversely, as holistically tailored to the individual patient. This is the focus of Section II. Despite being latent, variable, and unique to each patient, practitioners spent enormous time and energy trying to standardise erythema production so as to ‘dose’ ultraviolet radiation safely and effectively. This tension between standardisation and individualisation, the hallmarks of biomedicine and holism respectively, lay at the heart of a struggle to control and legitimise light therapy during its nascent growth and widespread appeal, c. 1890–1940. The MRC was not merely caught up in this struggle, which by the late 1920s had reached new heights; it facilitated both sides of it, to the confusion and anxiety of light therapy’s professional and lay proponents. Conceptualised as the anchor that would stabilise a raft of conflicting theories about dosing light, the solar erythema was invested with a tremendous amount of authoritative weight. Intriguingly, this was a role that it constantly resisted and undermined.

Photographs by British light therapists that depict solar erythema on patients’ skin (Figs. 2.2, 2.3) are no more legible than Finsen’s (Fig. 2.1). In Section II, I approach the solar erythema and its visual and written representations as resistant, unfixed, and uncooperative. Whether a risky product of excessive or mismanaged exposure, or the ‘delicious burning’ that marked the path to health, the solar erythema was an ambiguous sight in twentieth-century medicine and public health.⁸ I want to explore this ambiguity, with Finsen’s photographed forearm leading the way.

2.2 ‘Photograph showing erythema produced by graduated exposure of forearms to ultra-violet rays.’

In Eleanor H. Russell and William K. Russell, Ultra-violet Radiation and Actinotherapy (Edinburgh: E. & S. Livingstone, 1925), Figure 53, p. 153. Author’s collection.

2.3 ‘Exposure of arm to mercury vapour lamp for ten minutes.’

In Leonard Hill, Sunshine and Open Air: Their Influence on Health, with Special Reference to the Alpine Climate (London: Edward Arnold, 1925), Plate V, opposite p. 80. Author’s collection.

I  Setting standards

Niels Finsen is credited with the invention of phototherapy, which he employed primarily to treat lupus vulgaris (tuberculosis of the skin, Fig. 2.4). This was a particularly disfiguring disease with no known cure and most often attacked the face like the sexually transmitted disease, syphilis, with which it was often confused. Consequently, it forced sufferers to hide away from the public eye. By the end of the nineteenth century, as Anne Jamieson explained, it was generally agreed to be a form of external tuberculosis and bacterial in origin.⁹ Finsen was one of several international physicians and scientists experimenting with light to kill bacteria or to cauterise wounds during the nineteenth century, if not earlier.¹⁰ The light’s ability to burn lesions had been controlled and concentrated with lenses, but this was primarily due to its heating action. What made Finsen’s method different was his exclusive use of the blue, violet, and ultraviolet rays, what he called the ‘chemical’ or ‘actinic’ rays, by filtering and cooling the rays of sunlight through coated lenses and, later, those of artificial light generated from carbon arc lamps. Following new scientific evidence disseminated during the late 1870s and 1880s that ultraviolet light was bactericidal, he directed the actinic rays onto tubercular lesions to destroy the bacteria.¹¹

2.4 Before and after photographs of a patient suffering from lupus vulgaris.

In Niels R. Finsen, Die Bekämpfung des Lupus Vulgaris (Jena: Gustav Fischer, 1903), unpaginated. Author’s collection.

Finsen became aware of actinic light’s destructive powers by conducting experiments with sunlight in 1893, using himself as a test subject. In his first experiment he exposed his bare forearm to direct sunlight for three straight hours, including a two-inch band painted in India ink that he described as ‘blackened’ to ‘imitate the colour of the negro’s skin’.¹² (For more on colour and race, see Chapter 5.) The area protected by the ink, he stated, was unmarked after exposure, while the rest of his forearm showed ‘After some hours a very well-marked erythema, accompanied by pain and slight swelling’, which lasted for several days.¹³ Once healed and pigmented, he exposed his arm again, without painting the skin, noting that the previously covered portion that had remained white suffered badly this time from erythema. By contrast, the pigmented areas had naturally protected his skin. When he described the solar erythema, he explicitly understood it as an ‘eruption’ manifested from the ‘harmful influence of the chemical rays’.¹⁴ Finsen described solar erythema and pigmentation as sequential cutaneous reactions to this light using the language of disease: the first was an ‘acute’ manifestation and the second a ‘chronic’ one.¹⁵

In Finsen’s second experiment he exposed his forearm again to actinic light, but instead of sunlight he held it close to a carbon arc lamp for twenty minutes (Figs. 2.1, 2.5). Figure 2.5 presents the before and after photographs of the experiment, again poorly reproduced, here via the American physicist and lighting designer for General Electric, Matthew Luckiesh, with August John Pacini, in their 1926 book Light and Health. Luckiesh and Pacini offered details of the second experiment:

2.5 ‘Copies of original illustrations published by Finsen. Above are indicated the pieces of various media which he glued to his forearm. Below are the results of solar radiation illustrated. Much detail has been lost in reproduction.’

In M. Luckiesh and A. J. Pacini, Light and Health (Baltimore, Md.: The Williams & Wilkins Company, 1926), Figure 7, opposite p. 98. Wellcome Library, London CC BY-NC 4.0.

In the experiment, Finsen tested the transparencies of these different materials to the actinic rays, specifically seeking to understand which mediums would allow ultraviolet light to pass through them and which would not. The solar erythema that appeared three hours later, photographed the following day, was a cutaneous reaction he was counting on.¹⁷ Unlike the first experiment, he was not measuring his own skin’s sensitivity to actinic light or ascertaining the protective role of pigment. Rather in this second experiment his arm became a testing ground, a registration device akin to a sensitive photographic plate used contemporaneously in spectroscopy, for revealing the materials’ transmitting properties. By doing so, he used his own arm as a light register, a subject I explore in detail in Chapter 3. Finsen noted that solar erythema developed on the uncovered portions of his forearm and through the quartz glass, save for the bits of glue, but not on the skin covered by the coloured or clear ordinary glass plates and India ink. He concluded that quartz glass allows the actinic rays of light to pass through it, whereas ordinary glass does not.

As already noted, Finsen was not the first to distinguish between solar and heat erythema, nor was he the first to experiment on himself using an electric arc lamp.¹⁸ He was, however, the first to apply this knowledge to the therapeutic use of ultraviolet radiation and translate his experiments into a systematised treatment, which he called ‘phototherapy’. Following his exactitude and scientific methods, the Finsen Institute (f. 1896) integrated the clinic and the laboratory, providing a space for the direct observation and treatment of patients as well as experimentation with ultraviolet, X, and gamma rays.

Finsen’s initial experiments were followed by his novel modification of the carbon arc lamp, already used in street and theatre lighting, welding, and as searchlights, which became famously known as the ‘Finsen light’ or ‘Finsen lamp’ (Fig. 2.6). The modifications included shielding the arc of light and redirecting the emitting rays into telescopic arms, which filtered the light through a series of expensive quartz lenses (instead of ordinary glass lenses). The infrared and red rays were absorbed along the way, so as to avoid heat erythema, by colour filters and water flowing between the lenses. The lamp’s arms were pressed against the patients’ diseased skin by skilled nurses. An additional water-cooled lens was strapped directly to the patient’s face, compressing the skin and draining blood from the area to facilitate the light’s penetration (Fig. 2.7). By this method, the light directly targeted each lesion, requiring one to two hours of this localised treatment per area. Finsen’s laboratory assistant at the institute, Valdemar Bie, specified that, ‘In this manner an area of skin of about 1½ centimetre in diameter is treated for one hour every day. The treated skin reddens and swells, a bulla may appear, but necrosis has never been observed.’¹⁹ Others, like the medical superintendent of the Treloar Hospital for Crippled Children (Hampshire), Sir Henry Gauvain, reported using the Finsen lamp for up to two hours per lesion in 1925.²⁰

2.6 ‘The treatment by the electric light’, at the [Royal] London Hospital, c. 1900.

Wellcome Library, London CC BY-NC 4.0.

2.7 Photograph of patient with compressor.

In Niels R. Finsen, Phototherapy, trans. J. H. Sequeira (London: Arnold, 1901), Figure 6, opposite p. 70. Wellcome Library, London.

For Finsen, actinic light had similar properties to other kinds of chemicals by cauterising and irritating tissues; he complemented phototherapy with iodine and pyrogallic and boric acids on the lesions.²¹ Those who used his method asserted that it was painless for patients, despite noting the irritants used and the erythematic reactions following local treatment.²² As Jamieson pointed out, however, what constituted ‘painless’ must be understood in relation to the other methods for treating lupus vulgaris at the time, such as scraping and cutting the skin.²³ By comparison, phototherapy seemed tame for a disease that was notoriously difficult to treat. It was equally praised for its cosmetic results, the scar tissue perceived as soft, supple, and even.²⁴

While Finsen stated that exposing the patient’s entire body to actinic light could be beneficial (known as ‘full body’ or ‘general’ treatment), it is evident from phototherapy’s inception – used by Finsen primarily as a lesion-specific (‘local’) treatment – that ultraviolet light was prized precisely because of its damaging, bactericidal abilities. It is also clear from his early personal experiments that solar erythema played a weighty role: it was the anchor securing his claims that light, and especially ultraviolet light, could be used to great therapeutic effect.

Finsen was known throughout the world for his work with phototherapy, and Britain was no exception. He became internationally renowned for the treatment’s success and in 1903 won the Nobel Prize in Medicine. Through the intervention of Queen Alexandra (then Princess of Wales), Finsen’s methods and equipment were imported to the (Royal) London Hospital in 1899, where they instigated the birth of the ‘Light Department’, headed by Stephen Mackenzie and James Sequeira, in May 1900 (Fig. 2.8). The department employed phototherapy with carbon arc lamps and, to a lesser extent, heliotherapy using Finsen’s glass lenses (Fig. 2.9). One month after opening to patients, a report in the BMJ outlined its principles of light treatment:

1. That the chemical [blue, violet, and ultraviolet] rays of the sun or of the electric light can produce an inflammation of the skin.
2. That they can produce an effect through the skin.
3. That they can kill microbes on, in, or close under the skin.²⁵

2.8 ‘The Light Department, London Hospital, showing patients being treated with Finsen lamps for lupus.’

In William Beaumont, Fundamental Principles of Ray Therapy (London: H. K. Lewis & Co., 1931), p. 3. Author’s collection.

2.9 [Ernest Harnack], ‘Finsen’s apparatus for concentrating the sun’s rays’, courtyard of the [Royal] London Hospital, c. 1900.

In Ettie Sayer, Medical Electricity and Light (London: Scientific Press, 1913), p. 85. Thackray Medical Museum, Leeds.

Again, note that local phototherapy, employed especially for dermatological diseases, was defined by its power to do damage, both in its lethal action on bacteria and its inflammatory capacities on the skin. For this reason, early references to the blue, violet, and ultraviolet rays not only as ‘chemical’ or ‘actinic’ but also as ‘injurious’ occur frequently in light-therapy literature.²⁶ I return to this point at the end of the chapter, and again in Chapter 4, when discussing historic and contemporary perceptions about ultraviolet radiation and bodily damage.

 Exposure methods

Exposure methods varied widely among practitioners when it came to general treatment by actinic light, frequently described as a light ‘bath’ in either natural or artificial form. Differing perceptions about the roles of solar erythema and pigmentation were at the heart of these. Suffering from Pick’s Disease, Finsen died in 1904, but his institute in Copenhagen continued to flourish after his death. While it specialised in treating lupus vulgaris by local phototherapy, the physicians there also used general phototherapy and heliotherapy. Finsen discussed the potentials of general light baths already by 1895, and the institute employed them as a complement to local treatment from as early as 1900.²⁷ Combining the destructive action of local applications and the stimulating action of general applications, the Finsen Institute and, soon afterwards, the London Hospital, reported greatly increased rates of successful cures among lupus vulgaris patients.²⁸

The Finsen Institute’s Medical Superintendent, Axel Reyn, explained in 1923 that its method was to use artificial light for long general exposures on patients and to purposefully provoke a ‘pronounced erythema’ during the initial stages of treatment:

Reyn declared this method was in contradistinction to that used by the Swiss heliotherapist, Dr Auguste Rollier, who had employed heliotherapy from 1903 and who was arguably the most famous of light therapists (see Chapter 1).³⁰ Rollier avoided producing solar erythema in patients and favoured pigmentation. He claimed to have ‘systematised’ heliotherapy by his methods, gained through clinical experience and by his documentation, not least through the visual.³¹ Rollier began by carefully acclimating the patient to the sunlight of the Swiss Alps, in Leysin, by exposing body parts in short doses until deep pigmentation was acquired (Fig. 2.10). In his acclimation chart, Rollier segmented the patient’s body into regions of increasing photosensitivity, a visual device through which his heliotherapeutic practice emerged as standardised, minutely observed, and strictly managed. He first exposed the patient’s feet, then calves, thighs and so on at five-minute intervals per day. By this slow, graduated method of bodily exposure he avoided erythema production. But, like Reyn, and indeed many other light therapists, Rollier believed in long exposures to actinic light following the acclimation period, lasting several hours a day (in some cases every day for months or years), in order for his patients to derive full therapeutic benefit. As discussed in Chapter 5, pigmentation was conceptualised as a natural form of skin protection, a filter or ‘screen’ that could facilitate treatment – or hinder it. For Rollier, the suntan was a visual sign that the treatment was working. Those patients who bronzed well were perceived to be on the road to recovery, while those whose skin developed only a severe solar erythema were regarded ominously as lost causes. As the French heliotherapist Dr François Chiaïs put it, in 1907: ‘If pigmentation does not develop, the prognosis is most dire.’³²

2.10 ‘Our diagram of insolation. Progression according to which the sick [patient] is exposed to the sun.’

In Auguste Rollier, La Cure de soleil (Paris: Baillière & Fils; Lausanne: Constant Tarin, 1914), Figure 8, p. 65. Martine Gagnebin and author’s collection.

The exposure methods of the Finsen Institute in Denmark (referred to as the ‘Copenhagen technique’³³) and the ‘Rollier method’ in Switzerland were far from unanimously celebrated. British practitioners varied widely in their attitudes towards these methods, though great deference was shown to both. Heavy praise was given to the results and meticulousness of the Finsen Institute’s procedures. Indeed, Jamieson convincingly argued that, though difficult to replicate, the techniques, exactitude, and equipment of the institute contributed towards the production of a powerful ‘Finsen brand’.³⁴ Gauvain, who visited the institute on multiple occasions and modelled his own extended light department (1924) at Treloar’s on its layout, procedures, and equipment, imitated Reyn’s long exposure methods when using carbon arc lamps for general exposure.³⁵ So did many other British practitioners.³⁶ Yet Gauvain equally imitated the acclimation method of Rollier, favouring pigmentation and declaring that ‘sunburn’ was an undesirable reaction with dangerous consequences:

Others, including the highly respected British researchers Sir Leonard Hill and Albert Eidinow (NIMR), were particularly aware of the conflicting methods of Reyn and Rollier. They were equally critical of both. Hill and Eidinow faulted the Copenhagen technique for using light sources weak in ultraviolet radiation but abundant in heat rays for hours at a time, during which patients were confined to poorly ventilated rooms and sweated copiously.³⁸ They also disapproved of lengthy general exposures to the whole body whether by heliotherapy or phototherapy, because the development of pigmentation during these extended periods necessitated progressively higher, longer doses to provoke the desired solar erythema (which, unlike Rollier, they viewed as essential to the cure). As Eidinow put it, by this method the skin became ‘rapidly light-tolerant and immune’, where the natural protection that pigmentation afforded became an inhibitor to treatment because it desensitised the skin to ultraviolet radiation.³⁹ They viewed the goal of exposure to be the production of solar erythema without subsequent pigmentation, and, as such, distinguished their method from both the methods of the Danish and the Swiss.

Hill and his colleagues at the NIMR advocated short, intense exposures to ultraviolet light with quartz mercury vapour and carbon arc lamps. They devised a method of exposing areas of patients’ skin to lamps for only a few minutes at a time, every other day, ‘dosed’ according to what they called the ‘minimal perceptible erythema’ (MPE).⁴⁰ Hill and Eidinow defined the MPE as lasting less than forty-eight hours, potentially followed by peeling and not resulting in pigmentation. Their constant for determining MPE production was, in their words, ‘normal’ or ‘average’ white skin.⁴¹ In the many reports and articles they presented throughout the 1920s, they maintained that this kept the patient’s skin in a constant ‘light-sensitive’ state and was much cheaper in terms of electricity consumption.⁴² William Beaumont, medical director of the Institute of Ray Therapy in Camden, observed that shorter doses were also less ‘exhausting’ for patients, especially children.⁴³ Hill and Eidinow’s greatest criticism of the methods of Rollier as well as of the Finsen Institute was that, ‘No importance is attached to the biological response of the skin after radiation.’⁴⁴ By orientating light treatment entirely around the solar erythema, Eidinow and Hill claimed to have, like Finsen and Rollier before them, invented a ‘simple systematic technique’ to guide phototherapeutic practice.⁴⁵

 Wrestling control

Eidinow stated that any lamp emitting ultraviolet rays would work with their method, and though they developed it for phototherapy he stated it could potentially guide heliotherapy as well.⁴⁶ Importantly, they also viewed it as a step towards standardising light therapy, Hill stating in 1925:

Their compulsion to systematise and standardise light therapy according to qualifiable and quantifiable phenomena was indicative of a larger push by this time towards standardisation and controlled organisation, in medicine and science as well as in industry. Like radiologists, who were similarly struggling at the same moment to gain legitimacy as a group of specialised practitioners, light therapists turned to standardisation as a way to wrestle control over their equipment, their patients, and their reputation. Increasing dependence upon patient attendance records, budget ledgers, and dosage units are evidence of a shared experience among these ray technicians.⁴⁸

As employees of the MRC, Hill and Eidinow were also under the direction of its secretary, Walter Morley Fletcher, a man who privileged scientific research over the empiricism of clinical practice.⁴⁹ As key members of the MRC’s CBAL, Hill and Eidinow conducted a series of laboratory-based experiments on animal and human subjects with ultraviolet light. Significantly, this committee had existed since 1922, indicating an early interest by the MRC to ascertain scientific data about actinic light’s actions. In its report for 1923–24, it spoke of light therapy giving ‘new hopes … of a wide-spread diminution of disease and a great future improvement in the health, stature and beauty of the people in this country’, particularly with regard to its use for rickets.⁵⁰

Further pressured from the mid-1920s by the minister of health, who was receiving frequent requests to fund light clinics, the MRC needed to prove conclusively and scientifically that light therapy was truly effective.⁵¹ Dr Dora Colebrook, who acted as secretary of the CBAL and was already familiar with light therapy from her time at the North Islington Infant Welfare Centre, took on the task from 1926 to 1928. In his book, Control and the Therapeutic Trial, Martin Edwards argued that light therapy suffered its first major ‘scandal’ in 1929, when the MRC published the results of Colebrook’s randomised controlled trials. Colebrook conducted two trials, the first involving adults, treated by local phototherapy for varicose ulcers, and the second on schoolchildren, who were treated by general phototherapy to assess changes to their general health.⁵² In both trials her results indicated that the therapy had little medical value, with no perceptible improvement on patients’ conditions. The 1929 report presenting her findings shocked the medical community and was discussed not only in journals such as the BMJ and the Lancet but also in national and local newspapers.

Experienced clinicians took particular offence to Colebrook’s trials and were equally disturbed by the MRC’s sudden volte-face, having previously published favourable results and having among its members the highly respected practitioners Sequeira, Gauvain, and Hill. Crucially, for these practitioners the negative findings could be accounted for by incorrect technique and dosage. For instance, a passionate diatribe by Dr Maurice Weinbren, a light-therapy practitioner and radiologist with experience at Mount Vernon, Middlesex, and Queen’s Hospitals, pointed out the various faults of Colebrook’s studies and its ‘misleading’ results. He stated that Colebrook, in her ‘intensive’ study (sarcastically commented), only administered sub-erythemal doses on the varicose ulcers and only one to two times a week. Improperly dosed, the results, unsurprisingly for Weinbren, were poor.⁵³ As is clear, the visible production of solar erythema through local phototherapy was requisite in Weinbren’s mind. No redness, no effect. More vehemently, Dr F. W. Alexander (once medical officer of health for Poplar), was quoted in the Yorkshire Post as exclaiming, ‘I don’t understand what this report of the Medical Research Council is driving at. It seems utterly absurd. Nor do I know how they have given the treatment. Given properly, I know of no more powerful therapeutic treatment. Such criticism seems absolutely ridiculous.’⁵⁴ Manufacturers of light-therapy lamps also protested loudly, concerned about the knock-on effects to their sales. Gathering at a London meeting to discuss the ‘ultra-violet ray controversy’ and its ‘death blow at their industry’, the manufacturers pointed out that their distress was considerable and understandable: the industry employed 10,000 people, and they reported 30,000 medical practitioners in Britain were using light therapy.⁵⁵ The manufacturers, like many practitioners, called for more sufficient scientific trials to be done. In its defence, the MRC employed a ‘rhetoric of control’ to assert that Colebrook’s scientific test methods were systematically and rigorously undertaken according to Edwards, who viewed them as foundational to the use of randomised control trials.

Edwards’ argument presumed that light therapy, by being widely employed and popularly discussed among the medical community and the popular press, was, by 1929, already legitimate and established as ‘mainstream medicine’ – hence the ‘scandal’.⁵⁶ On the one hand, Finsen’s Nobel Prize (1903), Gauvain’s knighthood (1920), and ongoing royal sanctioning indicates that it was a legitimate medical therapy by this time. On the other hand, light therapy’s zealous use and popularity caused the MRC considerable distress from the early 1920s onwards, as Edwards himself showed, because few standardised guidelines about its application and methods existed. From the early 1920s, the MRC struggled to legitimise the therapy through various scientific and ‘controlled’ studies, yet that control was forever out of its grasp. There was tension even within its CBAL, the clinicians Sequeira and Gauvain indifferent and apparently unhelpful to Colebrook in her scientific trials.⁵⁷ Edwards positioned the 1929 ‘scandal’ as a major setback in the therapy’s history, concluding that by the 1930s it was already fizzling out in popularity.⁵⁸

Primary evidence suggests otherwise, as we will see throughout this book. But what of the effect of Colebrook’s results? For practitioners and manufacturers, light therapy’s reputation could be restored by more trials, more data, and thus more investment in it, presenting important similarities with the history of vitamins (see Chapter 1).⁵⁹ According to one journalist, the MRC report did little to diminish interest in the therapy, noting interestingly that following its publication the number of institutions offering light therapy increased:

Failures and errors when administering light were explained as the result of faulty technique, improper dosage, and lack of skill. Dr Allan Hamilton, of the Poplar Light Clinic, could not account for his poor results, and in his confusion he was equally sceptical of his own skill and his peers’ extravagant claims. He stated, rather poetically:

Jamieson explained that the same poor results occurred when using the Finsen lamp for lupus vulgaris patients, with failure attributed to bad technique, lack of attention to detail, the wrong equipment, and unskilled operators.⁶² In other words, it was not that the light was perceived as ineffective or that the therapy as a whole was to blame. Rather, blame lay with individual practitioners – Colebrook being an exemplary case. If Colebrook’s trials achieved anything, it was to confer even more attention onto light’s ‘handling and application’, centred on the issue of dosage.

II  ‘Fixing’ doses

As is clear from the opening article of The Times’ special 1928 ‘Sunlight and Health’ supplement, dosage standardisation preoccupied practitioners well before the MRC’s 1929 report: ‘Every year [from 1920 onwards], indeed, has brought with it, in addition to new observations and deductions, new doubts and difficulties. There is, as yet, no certain knowledge of the remote effects of artificial sunlight. There is no certain knowledge about the correct doses of artificial sunlight.’⁶³ Earlier, in a 1925 article in the Lancet, Eidinow expressed his anxiety over the lack of standards in measuring and regulating ultraviolet dosage:

For Eidinow, the sheer variety of lamps in use, emitting different wavelength ranges and intensities, negated the possibility of accurately comparing patient records from different hospitals and clinics. The same could be argued for sites around Britain using heliotherapy, since climatic and topographical differences (quite aside from seasonal variations) affected patients’ exposure to the sun’s ultraviolet radiation. As with other drugs, light rays – especially ultraviolet rays – produced different effects on the patient according to quantity, Beaumont clarifying by analogy with opium:

Here Beaumont neglected to mention the dangers of an overdose, a matter that clearly concerned Eidinow as the above quote indicates.

What fascinates me is that Eidinow, along with his colleagues at the NIMR, devoted themselves to the very thing he described as impossible: the task of ‘fixing’ a standard therapeutic dose of ultraviolet radiation. The various meanings of the verb ‘to fix’ are significant when we consider its applications in science, medicine, and art: to fix a scientific principle or standard is ‘to secure’ it or ‘to make (it) permanent’; to fix a broken leg is ‘to mend’ it, ‘to set (it) right’ or ‘to secure (its) position’; to fix an image is ‘to make (it) permanent’ or ‘to secure’ it. The very invention of photography depended upon this matter of ‘fixing’; the ability not to simply record impressions onto surfaces but to keep them there marked the official beginnings of photography in the 1830s. Ironically, the very source that produced those impressions, namely light, could erase them by means of prolonged exposure. In her book, The Burning Mirror, Melissa Miles has discussed the frustrations experienced by early photographers in experimenting with light, revolving around the issue of control: ‘The desire to develop an agent that would “fix” photographs, and thereby exert “a protecting power” against the sun’s rays, can … be understood as a struggle to stabilise this troubling ambivalence and construct light as a productive origin for photographic image-making.’⁶⁶ Unless they could be made permanent, producing images with light had little value in disseminating information.

The struggle to make permanent or stabilise the light’s imprint on the photosensitive emulsion, requisite to legitimising photography as a recording medium, finds important correlations with light therapy’s problematic investment in dosage standardisation as a means to legitimisation. Finsen’s photographed forearm presents a convergence of photography’s and light therapy’s drive to ‘fix’ (Figs. 2.1, 2.5). Its fuzzy contours and misty patches are evidence of insufficient fixing in the taking and developing of the photograph, obscuring the legibility of the solar erythema manifest on Finsen’s skin. In the version in Figure 2.5, underexposure in the reproduction process has created so much loss of contour and so much darkness as to literally obscure clear reading of the ‘after’ photograph. Even the authors, Luckiesh and Pacini, point out this problem in the image caption: ‘Much detail has been lost in reproduction.’

When it came to the ‘impossible’ task of fixing a standard dose of light, Hill and Eidinow undertook several experiments at the NIMR, under the auspices of the MRC. Different methods for measuring ultraviolet light included chemical and ‘biological’ tests, by bleaching coloured solutions and irradiating test subjects to determine standard units of measurement. The most successful measurement in the end was according to erythema production on the skin, as Finsen had done.⁶⁷ Eidinow took it as a given that erythema production signalled ultraviolet radiation’s consequent therapeutic ‘value’, a reference to its medical worth but one ironically residing in ambiguous, unfixed gradations of light and dark in photographic representation (Figs. 2.1–2.3).⁶⁸ For the test, they covered the skin with fabric, save for three circular flaps that would be opened at succeeding intervals. Hill explained that the first exposure was five minutes, the second ten minutes, and so on.⁶⁹ Black-and-white photographs indicate this testing method was performed according to different numbers of openings, different times of exposure, and different environmental conditions (Figs. 2.2–2.3).

Contemporaneous British images of MPE testing also include hand-drawn illustrations (Fig. 2.11).⁷⁰ In Figure 2.11, a drawing from Dr Hugh Morris’s Physiotherapy in Medical Practice of 1939 presents the test set-up, including placement of black paper on the patient’s forearm and indications to cover the rest of the skin with towels. This proved to be the cheapest and easiest of methods for testing, with materials easy to hand and hygienically discarded, just as sheets of dark paper came to be used to shield patients’ eyes instead of expensive goggles.⁷¹

2.11 ‘To illustrate method of testing the sensitivity of a patient to ultraviolet radiation.’

In Hugh Morris, Physiotherapy in Medical Practice (London: Edward Arnold, 1939), Figure 92, p. 188. Author’s collection.

Hill and Eidinow, working with bacteriologist Dr Leonard Colebrook (Dora Colebrook’s brother), further correlated erythema production with the blood’s increased bactericidal powers, and this is a major reason they privileged short doses that produced solar erythema without subsequent pigmentation. But even here they cautioned that standardising ultraviolet dosage according to blood testing required more time and resources than MPE testing, and it was complicated by the fact that human blood was already normally high in bactericidal properties. Worryingly, their tests had shown that an overdose of ultraviolet light could actually lower the blood’s ability to kill bacteria, putting the sick patient even more at risk.⁷² In the end, the researchers’ choice was clear: ‘The treatment should be controlled by the erythema produced.’⁷³

Eidinow invented his own equipment for the purpose (known as the ‘Eidinow test-dosage armlet’), likely used for the erythema test in a photograph provided by Drs Eleanor H. Russell and William K. Russell (Fig. 2.2).⁷⁴ As with Figure 2.1, the Russells’ photograph obscures the subtle gradations (‘values’) of erythema production on the forearms, which have been used together in this instance as registers for eight sequential one-minute exposures. Similarly, in his 1925 Sunshine and Open Air, Hill included photographs presenting the results of forearms irradiated through armlets while under various surrounding temperatures or through interposing materials (Fig. 2.3). Much like Finsen’s photographed forearm, the arms register the effects of ultraviolet light through cold versus warm water (photograph 1), during hot, normal, or freezing temperatures (photograph 2), as well as through black-and-white coloured fabric (photograph 3). Both Finsen’s and Hill’s experiments tested materials mediating contact between ultraviolet light and the body, acting as either aids or hindrances, and these practitioners interpreted their findings by perceiving solar erythemata as explicit visual referents.

Aside from Eidinow’s armlet, other erythema test kits were invented for determining dosage. The most elaborate device was invented by the influential French practitioner Dr Jean Saidman, creator of the equally elaborate ‘Turning Solarium’ (Aix-les-Bain, Vallauris, Jamnagar) and Gauvain’s associate. Saidman’s ‘sensitometric test’ or the ‘Saidman Sensitometer’ (Figs. 2.12–2.13), patented in 1927, incorporated a clockwork shutter to expose areas of the patient’s abdomen or thigh by eighteen one-minute intervals, imprinting onto the skin its intricate design of shapes and numbers in the form of solar erythema. By this means Saidman determined the individual patient’s ‘seuil d’érythème’ – their erythemal threshold.⁷⁵ Yet once again, when we defer to the visual records, the subtle values of erythema intensities elude photographic representation (Fig. 2.13). Some of the shapes appear more faded than others, suggesting possibly that these indicate lower doses, but the fading could equally have been produced in the process of taking, developing, or reproducing the photograph.

2.12 ‘Sensitometric test of Dr Saidman’ (illustration of device).

In Dr Stoïanoff, ‘Actinométrie, héliométrie’, in Charles Brody (ed.), Traité d’hélio- et d’actinologie (Paris: Maloine, 1938), vol. I, Figure 211, p. 392. Author’s collection.

2.13 ‘Sensitometric test of Saidman’ (before and after photographs).

In Hubert Jausion, ‘L’Héliodynamothérapie des alopécies’, in Charles Brody (ed.), Traité d’hélio- et d’actinologie (Paris: Maloine, 1938), vol. II, Figures 577–8, p. 1185. Author’s collection.

These scientific investigators looked to photography as a medium to record and disseminate their findings. This in itself is certainly not surprising, as photography held tremendous authority for ‘objectively’ recording and disseminating science and medicine as Lorraine Daston and Peter Galison make clear.⁷⁶ But photography’s relationship with light therapy was made fascinatingly tangled and uneasy by virtue of the fact that they were both, in Tanya Sheehan’s words, ‘technologies of light’.⁷⁷ The poor legibility of the solar erythema in these photographs (Figs. 2.1–2.3, 2.5, 2.13) can be accounted for by some very difficult and specific conditions.

One relates to photographic processes, particularly difficulties achieving correct lighting and focusing, proper developing, and reproduction, which are all affected by the skill and available equipment of the producers. These are, of course, the challenges of producing and reproducing any analogue photograph, then as now, but photographing light therapy presented extraordinarily tricky circumstances, especially when the lamps were turned on as they produced overexposed and damaged negatives, as I discuss in Chapter 3.

Another condition, with respect to photographing solar erythema specifically, relates to the difficulties of capturing an elusive and uncooperative subject. In photographs, practitioners’ audiences were presumably meant to encounter visual evidence of the efficacy of these erythema-centred tests. This was their intended function. But what is represented instead is evidence of a physiological phenomenon resistant to legible visual (re)presentation, to being clearly ‘fixed’. In the photographic evidence, the subtly varied values, if not the very presence, of solar erythema remain illegible. Which of the hazy marks is the ‘just perceptible’ MPE in these photographs? Could it be represented photographically?

In Figure 2.2, the four-minute mark looks darker and more defined than the five- and six-minute marks, when logically it should appear fainter, lighter, and less distinct. Such photographs therefore act as records, yes, but not of the solar erythema clearly measured, defined, and standardised. Rather, they record practitioners’ desperation to secure the solar erythema as a visual anchor, one that could legitimise the therapy yet refused to do so – it refused its authoritative role, refused to be weighed down. The drive to ‘fix’ the solar erythema, in visual and written form, says much about practitioners’ ambitions to make light therapy appear as a modern, scientific, and systematic treatment.⁷⁸

 The erythema materialised

Quantifying, qualifying, and visually analysing solar erythema preoccupied British practitioners, far more so than pigmentation ever did.⁷⁹ Many followed Hill and Eidinow’s test methods, and by 1927 the ‘spot test’ was already being described as well known.⁸⁰ In the first (1933) edition of the Actinotherapy Technique handbook, produced by the major lamp manufacturer Hanovia (Slough), the editors explicitly noted that lamps emitting any quantity of ultraviolet light, and indeed the very ‘technique of ultra-violet irradiation’, were to be ‘standardized on erythema reactions’.⁸¹ In this edition they included a chart presenting particular degrees of solar erythema, qualified and quantified by the visual physiological referents of peeling (desquamation), blisters, and colour intensity, as well as by measurable amounts of time, including both its latent appearance and its duration (Fig. 2.14).

2.14 ‘Erythema chart (for first exposure).’

In Actinotherapy Technique (Slough: Sollux, 1933), pp. 42–3. Author’s collection.

The information presented in Figure 2.14 is fairly consistent with other contemporaneous medical texts, with slight variations in descriptions, suggesting that the solar erythema was broadly mapped out and subdivided in this way from the mid-1920s.⁸² Interestingly, the chart employs the same vocabulary as heat burns, with the third and fourth degrees of solar erythema roughly corresponding to first- and second-degree burns.⁸³ A mild or first-degree erythema (MPE), it explained, lasted for only twenty-four hours; the second degree resulted in fine peeling and the third degree on a larger scale, while the fourth degree produced blisters.

Practitioners explained that solar erythema was the result of ‘irritation of the deep cells and nerve endings of the epidermis’, capillary dilation and increased blood flow (hyperaemia), and fluid in the tissues (oedema).⁸⁴ If sufficiently intense, as we can see with the fourth degree (Fig. 2.14), it could cause blisters and even necrosis of skin cells. In some cases these were desirable reactions – it depended upon the physician’s preferred method, the disease, and its specific treatment course.⁸⁵ Beaumont explained that, ‘The formation of a blister is not necessarily a sign of overdosage if it results from local treatment […] It is quite wrong, however, for blisters to be allowed to result over a large area from general irradiation.’⁸⁶ Therefore, at least for some practitioners, desirable erythema degrees were relative to local (lesion-specific) versus general (full body) exposures. The series of Actinotherapy Technique handbooks is organised in part by diseases, with recommended courses of treatment dependent on erythema degrees. The series indicates that erythema production went beyond its use value in the initial test to determine dosage, guiding the treatment throughout its course as an ongoing visual referent. Even Hanovia, in a 1940 user manual for the ‘Homesun’ lamp, advised the public to base initial and ongoing exposures according to MPE production:

As the manual stated, erythema production also signalled the bulb’s efficacy, the skin’s photosensitivity acting as a natural photometer for the equipment.

It was common practice for practitioners to use their own arm as a test subject for a lamp’s output, no doubt partly in deference to Finsen (Figs. 2.1, 2.5). Hill would do this, for example, and Actinotherapy Technique (1933) recommended self-testing as the best way to standardise one’s lamp.⁸⁸ Likewise, Hamilton declared that the minimal erythema dose could be ‘easily done by experimenting on yourself and your friends, and in this way you soon get a rough idea of its energy’.⁸⁹ He also reported using the lamps on the Poplar Light Clinic’s nurses to test skin reactions and dosages.⁹⁰ The operator’s skin therefore acted as the standard register for determining dosage. Far from being perceived as the ennobling act of the early X-ray martyrs, whose amputated limbs marked their self-sacrifice to medical progress, this was considered routine practice for assuring high standards of treatment.

In practice, dosage was administered to patients with the same standardised values in mind. Patients’ positions, for instance, were highly regulated to ensure correct dosage at the correct distance, angle, and time (Figs. 2.15–2.16). Often they were encouraged to be mobile, circulating around a single lamp or placed in an area surrounded by multiple lamps.⁹¹ One recommended technique was to set up phototherapy treatment with multiple lamps in a circle, enclosing an area that was subdivided into concentric ‘dosage circles’.⁹² Patients were then treated in groups, according to height, and they walked continuously during treatment within their designated track so as to expose their bodies evenly at the correct distance. It is reminiscent of exercising prisoners, as represented by Gustave Doré in William Blanchard Jerrold’s London: A Pilgrimage (1872).⁹³ The physical set-up of treatment sites and equipment acted as Foucauldian regulatory mechanisms not unlike Eidinow’s ‘test-dosage armlet’, Saidman’s ‘sensitometer’ or Rollier’s and Hanovia’s charts.⁹⁴ Together these material objects directed light-therapy practice, made it tangible (‘materialised’), ordered, and standardised. Or at least they made it appear to be standardised; the unstable character of the solar erythema, on which these regulatory mechanisms depended, constantly undermined practitioners’ efforts.

2.15 Phototherapy room with fenced ambulatory at fixed distance, Grange Road Clinic, Bermondsey, 1937.

Southwark Local History Library and Archive, Wellcome Images, London CC BY-NC 4.0.

2.16 ‘Irradiation with Jesionek quartz mercury vapour lamp at a general hospital. (Note the dosage circles described on the floor.)’

In Eleanor H. Russell and William K. Russell, Ultra-violet Radiation and Actinotherapy (Edinburgh: E. & S. Livingstone, 1925), Figure 48, p. 142. Author’s collection.

 Sign and signature

Hanovia’s chart provides vague descriptions of colour, from ‘slight’ to ‘very intense’ reddening, with no visual complement (Fig. 2.14). In the photographs of solar erythema production (Figs. 2.1–2.3, 2.5, 2.13), the limitations of black-and-white photography to define and classify this phenomenon become especially resonant. Placed alongside Hanovia’s chart, is the Russells’ photograph (Fig. 2.2) more or less clear in (re)presenting erythema production? Does the written word succeed where the visual fails? Would a colour chart, with varying intensities of red, instead have made the task of grading and identifying erythema values any better or easier for practitioners?⁹⁵ Perhaps not. It would have had to have accounted not only for varying intensities of red (first to fourth degrees) but also these intensities produced on varying tones of skin colour (natural or already pigmented by prior exposure), necessitating not one but multiple colour charts. The Swiss heliotherapist Oskar Bernhard stated that colour values of the solar erythema were also dependent upon the light source, without regard for the degree. A ‘bluish-red erythema’ was caused by the ultraviolet-rich light of the mercury vapour lamp, he stated. But a ‘strong red full-blooded erythema’ was produced by a carbon arc lamp, which, like sunlight, gave off plenty of heat but relatively little ultraviolet light.⁹⁶

The overall absence of the solar erythema in visual representation might be simply explained by the limitations of various mediums: colour photography was not widely available until the mid-1930s and colour lithography was expensive. This is not to say definitively that they did not exist but that they were not reproduced or referenced in the primary literature, such as manuals, textbooks, trade catalogues, or dissertations. In other words, even if they did exist they were not disseminated or discussed within the field among practitioners and so logically could not have been in general use. Instead we find written charts (Fig. 2.14) or more affordable black-and-white photographs (Figs. 2.2–2.3).

The solar erythema’s un-‘fix’-able nature, its fickleness, can be partially accounted for by the issue of latency. In addition to varying colour gradations to identify degrees, the timing for the solar erythema’s appearance was not defined with any consistency in the literature. Statements by British practitioners from the 1920s and 1930s give varied descriptions about its latent appearance, ranging from ‘almost immediately’ to eight hours.⁹⁷ Similarly, the erythema’s duration varied widely. It could disappear within twenty-four hours, as explained in the chart under the first-degree erythema (Fig. 2.14) but also persist between three days and several weeks according to other sources.⁹⁸

Hanovia’s chart presented a complicated, impressive series of numbers and categories: for different degrees of erythema, graded by differing colour intensities, extent of peeling or blistering; for different distances; for different lengths of time, by lamps of different types, models, years of manufacture, and voltage. Yet, at the bottom, it retained an important proviso: ‘This chart is not a hard and fast guide. It is provided as a working basis only; each patient must be treated as an individual.’⁹⁹

Above all, each patient reacted differently to ultraviolet radiation. Each had his or her own unique erythematic signatures. Recall that Eidinow declared, ‘The individual variations in sensibility to light make it impossible to fix a standard dose, even with a standard source of light’ (see statement above). This was not a new revelation; Finsen discussed individual variations in reactions to actinic light already by 1897.¹⁰⁰ It was mentioned in The Times’ 1928 supplement and was commonly remarked upon in medical texts.¹⁰¹ Some even gave up on the idea of dosage standardisation altogether, so unique were patient’s erythematic reactions. Dr C. B. Heald claimed in 1929 that,

When it came to patient photosensitivity, ‘No two patients are alike’, the Russells declared. They added that, ‘One would have a severe reaction with an exposure which would cause only the slightest reddening in another person.’¹⁰³ And yet, unlike Heald, they could not resist the impulse to generalise and categorise patient types, immediately confounding their statements by stating,

Patients’ so-called individual variations were grouped together and classified, dependent upon factors like race (skin, eye, and hair colour), gender, and age.¹⁰⁵ Children, women, the fair-skinned, and the red-haired were generally, though not always, considered to be more sensitive to actinic light. Practitioners disagreed, for instance, as to whether babies’ skin was more or less sensitive to ultraviolet light than adults’, with diverse exposure times as a result (see Chapter 5). Such unpredictable variations and diverse opinions led Gauvain to declare, as late as 1934, that light therapy was an ‘art’ rather than ‘an exact science’. In the same publication he even noted that patients’ reactions varied throughout their lives, according to their state of health, location, and season.¹⁰⁶

For George Weisz, Christopher Lawrence, and David Cantor, this focus on the individual patient characterised holism’s approach to medicine, which resulted from dissatisfaction with the reductionist view of biomedicine that treated diseases, not people. According to Lawrence, standardisation in medicine was a problem holists disparaged.¹⁰⁷ Holists were not necessarily alternative practitioners; Lawrence and Weisz pointed out that holist approaches occurred within mainstream medicine.¹⁰⁸ Some practitioners of light therapy were identifiably holists, including Dr Alexander Cawadias (Physician to the St John Clinic and Institute of Physical Medicine in the 1930s), but as these historians also noted that it is difficult to slot particular practitioners into the movement.¹⁰⁹ Indeed, light therapy seems to have integrated the reductionism and standardisation of biomedicine, especially through dependence upon laboratory research, with the individualisation associated with holism – if not muddled the clear distinction altogether. While some historians have discussed light therapy (especially heliotherapy) in relation to holism, others have aligned it with the emergence of biomedicine in the twentieth century. Cantor, for example, wrote that,

Cantor’s inclusion of phototherapy as part and parcel of a distinctly modern ‘standard set’ of therapies was certainly not an historical error. As we have seen, practitioners anxiously pushed to standardise dosages. Yet they also recognised the uniqueness of individual patient’s photosensitivities, manifested through erythema production. In this sense they could simultaneously be seen as holistic in their approach to administering the treatment to their patients.

In the case of light therapy, these were not necessarily contradictory practices, expressive of a seductive narrative setting up biomedicine versus holism, standardisation versus individualisation, or the laboratory versus the clinic. Individual practitioners vacillated between these apparent poles. Gauvain welcomed an MRC-funded laboratory researcher at Treloar Hospital in 1925, only to state the same year that, ‘While many important investigations on the mode of action of light have been completed in the laboratory the subject is so complex, so many factors are involved, that I believe clinical experience is still our most reliable guide.’¹¹¹ And the Swiss heliotherapist, Rollier, whose chart regimented the patient’s acclimation to sunshine according to strictly monitored times and bodily locations (Fig. 2.10), stressed that ‘no physiotherapeutic method demands such strict individualization as heliotherapy’.¹¹² For Rollier, the patient’s course of exposures, in addition to sleep, diet, and exercise, could be simultaneously individualised and regimented. As Michel Foucault argued, the unique emerges from and seeps through the norm:

From this it seems practitioners’ anxious drive to make light therapy a systematic and legitimate treatment by ‘fixing’ standard doses only succeeded in rocking the boat. That they chose the unique, variable, and latent solar erythema as an anchor merely destabilised their efforts even further.

Conclusion

All of the images and objects I have presented in this chapter about solar erythema point to a certain and rather fascinating tension in light therapy: between, on the one hand, recognising that patients were individuals with unique erythematic signatures and, on the other hand, attempting to force these highly variable photosensitivities to conform to a mass system. With photographs (Figs. 2.1–2.3, 2.5, 2.13), charts (Figs. 2.10, 2.14), testing devices (Figs. 2.11–2.12), and ‘dosage circles’ (Figs. 2.15–2.16) orientated around the production of solar erythema (or, in Rollier’s case, its avoidance), practitioners invested enormous energy to standardise dosage and systematise light therapy. With these objects in mind it is evident that this drive to control was more than rhetorical, as Edwards argued: it was material.

Throughout this chapter I have not been arguing that the solar erythema, or ‘sunburn’, was poorly defined or poorly standardised. This would suggest a lack of effort. On the contrary, the images and texts demonstrate that, despite the repeated efforts by clinicians and laboratory researchers to pin down this transient physiological reaction, the solar erythema resisted its role, just as it remained unreadable in visual representations. Its slippery character confounded standardisation, evaded the goals intended for it, and refused to be anchored down. Well before the MRC’s scandalous 1929 report of Colebrook’s trials, light-therapy practitioners were desperately trying to make the solar erythema a constant in their experiments in spite of recognising its intrinsically variable character; that is, to ‘fixing’ something inherently unfixable. As Hanovia’s chart (Fig. 2.14) makes evident, written descriptions were no clearer in pinning down the solar erythema than were images. But it is striking to note the difference in volumes of production between word and image here. The sheer amount of words dedicated to explaining, defining, and classifying solar erythema significantly outweighed the few visual representations devoted to the same tasks. The excess of the former reveals a desire to standardise not simply the solar erythema but the very practice of light therapy. The relative absence, illegibility or silence of the latter ironically speaks volumes about the impossibility of fulfilling that desire and the anxiety propelling it. The irradiated photographed forearms of Finsen (Fig. 2.1), the Russells (Fig. 2.2), and Hill (Fig. 2.3), obscure rather than illuminate, representing the solar erythema as unstable, resistant, and illegible. These so-called limits of the visual, then, are powerful and productive because they communicate much about light therapy’s worth and aims through an aesthetics of light. Put simply, the images matter because they tell us about light therapy’s medical, social, and aesthetic ‘values’.

Furthermore, in this chapter I have deliberately focused on solar erythema as a physiological phenomenon perceived to be simultaneously desirable and dangerous (or ‘injurious’) by practitioners over some forty years, showing that this tension was at work in light therapies from their inception in the 1890s. These contentious perceptions are manifested and produced by the slippages in the terminology itself – of solar erythema and/as ‘sunburn’.¹¹⁴ Even within the same camp of practitioners (Hill and Eidinow) and in the same year (1925) we encounter confusing explanations of the word: Hill described sunburn as an ‘excessive action of the sun’ that ‘floods the body’ and produces tissue damage; Eidinow claimed that sunburn was indicative of ultraviolet light’s therapeutic value.¹¹⁵

Already by 1940 solar erythema was described as an explicit form of bodily damage.¹¹⁶ Shifting to the present (2016), we continue to encounter conflicting visual and written messages about the meaning and role of sunburn. On its website, Cancer Research UK described sunburn as ‘a clear sign that ultraviolet (UV) radiation from the sun or sunbeds has damaged the genetic material in … skin cells’.¹¹⁷ Suntan is described as the ‘skin’s response to damage from the sun’.¹¹⁸ With its emphasis on visual and physiological damage, the charity characterised sunburn and suntan in ways with which we are now familiar; that is, by employing descriptors of risk and danger. Likewise, the British Association of Dermatologists listed ‘sunburn’ as the first ‘side effect’ of contemporary phototherapy, yet in its numerous leaflets it repeatedly included the phrase, ‘Never let your skin burn!’ to educate the public about the dangers of skin cancer.¹¹⁹ Degrees of solar erythema were not explained on its website, in words or images, presenting ‘sunburn’ as a particularly ambiguous term. I explore burns further in Chapter 4, but for now let me emphasise that the burn in ‘sunburn’ is but one unstable referent in the slippery vocabulary of light therapy.

The weight given to the solar erythema in the drive to standardise light therapy, beginning in the 1890s, continues today. Erythema production retains its visual authority in designating light dosages. It has carried through to regulations for ultraviolet radiation dosage standards in medicine (phototherapy), public health (notably the UV Index and in determining ‘phototypes’) and industry (including general occupational risk assessment).¹²⁰ In spite of overt awareness that individual photosensitivities are unique and subjectively graded (as well as racially specific), the solar erythema occupies an unchallenged position by phototherapists in the dosing of ultraviolet light, complemented increasingly by sophisticated photometric devices.¹²¹ It is true that it has been my aim to present not simply a diverse array but rather a disarray of written and visual material. But by looking carefully at the therapy’s visual ‘evidence’ it becomes clear that focusing on the things that do not make sense in its history – the disagreements, the ambiguities, the absences, and silences – is a tremendously productive way to contextualise Britain’s ongoing complicated and contentious relationship with actinic light.