Light therapy — or phototherapy, classically referred to as heliotherapy — consists of exposure to daylight or to specific wavelengths of light using polychromatic polarised light, lasers, light-emitting diodes, fluorescent lamps, dichroic lamps or very bright, full-spectrum light. The light is administered for a prescribed amount of time and, in some cases, at a specific time of day.
Light therapy which strikes the retina of the eyes is used to treat diabetic retinopathy and also circadian rhythm disorders such as delayed sleep phase disorder and can also be used to treat seasonal affective disorder, with some support for its use also with non-seasonal psychiatric disorders.
- 1 Medical uses
- 1.1 Skin conditions
- 1.2 Retinal conditions
- 1.3 Mood and sleep related
- 1.4 Neonatal jaundice (Postnatal Jaundice)
- 2 Techniques
- 3 Risks and complications
- 4 History
- 5 See also
- 6 References
- 7 External links
The treatments involve exposing the skin to ultraviolet light. The exposures can be to small area of the skin or over the whole body surface, like in a tanning bed. The most common treatment is with narrowband UVB (NB-UVB) with a wavelength of 311-313 nanometer. It was found that this is the safest treatment. Full body phototherapy can be delivered at a doctor's office or at home using a large high power UVB booth.
Light therapy is considered one of the best monotherapy treatments for atopic dermatitis (AD), when applied to patients who have not responded to traditional topical treatments. The therapy offers a wide range of options: UVA1 for acute AD, NB-UVB for chronic AD, and balneophototherapy have proven their efficacy over the recent past. Patients tolerate the therapy safely but, as in any therapy, there are adverse effects and care should be taken in its application, particularly to children.
For psoriasis, UVB phototherapy has been shown to be effective. A feature of psoriasis is localized inflammation mediated by the immune system. Ultraviolet radiation is known to suppress the immune system and reduce inflammatory responses. Light therapy for skin conditions like psoriasis usually use NB-UVB (311 nm wavelength) though it may use UV-A (315–400 nm wavelength) or UV-B (280–315 nm wavelength) light waves. UV-A, combined with psoralen, a drug taken orally, is known as PUVA treatment. In UVB phototherapy the exposure time is very short, seconds to minutes depending on intensity of lamps and the person's skin pigment and sensitivity. The time is controlled with a timer that turns off the lamps after the treatment time ends.
One percent of the population suffer from vitiligo, and narrowband UVB phototherapy is an effective treatment. "NB-UVB phototherapy results in satisfactory repigmentation in our vitiligo patients and should be offered as a treatment option."
Evidence for light therapy and lasers in acne vulgaris as of 2012 is not sufficient to recommend them. There is moderate evidence for the efficacy of blue and blue-red light therapies in treating mild acne, but most studies are of low quality. While light therapy appears to provide short term benefit, there is a lack of long term outcome data or data in those with severe acne.
According to the American Cancer Society, there is some evidence that ultraviolet light therapy may be effective in helping treat certain kinds of skin cancer, and ultraviolet blood irradiation therapy is established for this application. However, alternative uses of light for cancer treatment – light box therapy and colored light therapy – are not supported by evidence. Photodynamic therapy (often with red light) is used to treat certain superficial non-melanoma skin cancers.
Other skin conditions
Phototherapy can be effective in the treatment of eczema, atopic dermatitis, polymorphous light eruption, cutaneous T-cell lymphoma and lichen planus. Narrowband UVB lamps, 311–313 nanometer is the most common treatment.
Low level laser therapy has been studied as a potential treatment for chronic wounds. Reviews of the scientific literature do not support the widespread use of this technique due to inconsistent results and low research quality. Higher power lasers have also been used to close acute wounds as an alternative to stitching.
Seasonal affective disorder
The effectiveness of light therapy for treating SAD may be linked to the fact that light therapy makes up for lost sunlight exposure and resets the body's internal clock. Studies show that light therapy helps reduce the debilitating and depressive behaviors of SAD, such as excessive sleepiness and fatigue, with results lasting for at least 1 month. Light therapy is preferred over antidepressants in the treatment of SAD because it is a relatively safe and easy therapy.
It is possible that response to light therapy for SAD could be season dependent. Morning therapy has provided the best results because light in the early morning aids in regulating the circadian rhythm.
A 2007 systematic review by the Swedish agency SBU found insufficient evidence that light therapy was able to aleviate symptoms of depression or seasonal affective disorder. The report recommended that: "Approximately 100 participants are required to establish whether the therapy is moderately more effective than placebo". Although treatment in light therapy rooms was well established in Sweden, no satisfactory, controlled studies had been published on the subject. This lead to the closure of a number of clinics offering light therapy in Sweden.
Light therapy has also been suggested in the treatment of non-seasonal depression and other psychiatric mood disturbances, including major depressive disorder, bipolar disorder and postpartum depression. A meta-analysis by the Cochrane Collaboration concluded that "for patients suffering from non-seasonal depression, light therapy offers modest though promising antidepressive efficacy." A 2008 systematic review concluded that "overall, bright light therapy is an excellent candidate for inclusion into the therapeutic inventory available for the treatment of nonseasonal depression today, as adjuvant therapy to antidepressant medication, or eventually as stand-alone treatment for specific subgroups of depressed patients." A 2015 review found that supporting evidence for light therapy was weak due to serious methodological flaws.
Circadian rhythm sleep disorders and jet lag
- Chronic Circadian Rhythm Sleep Disorders (CRSD)
In the management of circadian rhythm disorders such as delayed sleep phase disorder (DSPD), the timing of light exposure is critical. Light exposure administered to the eyes before or after the nadir of the core body temperature rhythm can affect the phase response curve. Use upon awakening may also be effective for non-24-hour sleep–wake disorder. Some users have reported success with lights that turn on shortly before awakening (dawn simulation). Evening use is recommended for people with advanced sleep phase disorder. Some, but not all, totally blind people whose retinae are intact, may benefit from light therapy.
- Situational CRSD
- Sleep disorder in Parkinson's disease
Light therapy has been trialed in treating sleep disorders experienced by patients with Parkinson's disease.
Neonatal jaundice (Postnatal Jaundice)
Light therapy is used to treat cases of neonatal jaundice through the isomerization of the bilirubin and consequently transformation into compounds that the newborn can excrete via urine and stools. A common treatment of neonatal jaundice is the bili light or billiblanket.
Photodynamic therapy is a form of phototherapy using nontoxic light-sensitive compounds that are exposed selectively to light, whereupon they become toxic to targeted malignant and other diseased cells
The production of the hormone melatonin, a sleep regulator, is inhibited by light and permitted by darkness as registered by photosensitive ganglion cells in the retina. To some degree, the reverse is true for serotonin, which has been linked to mood disorders. Hence, for the purpose of manipulating melatonin levels or timing, light boxes providing very specific types of artificial illumination to the retina of the eye are effective.
Light therapy uses either a light box which emits up to 10,000 lux of light at a specified distance, much brighter than a customary lamp, or a lower intensity of specific wavelengths of light from the blue (460 nm) to the green (525 nm) areas of the visible spectrum. A 1995 study showed that green light therapy at doses of 350 lux produces melatonin suppression and phase shifts equivalent to 10,000 lux white light therapy, but another study published in May 2010 suggests that the blue light often used for SAD treatment should perhaps be replaced by green or white illumination, because of a possible involvement of the cones in melatonin suppression.
In treatment, the patient's eyes are to be at a prescribed distance from the light source with the light striking the (lower) retina. This does not require looking directly into the light.
Considering three major factors – clinical efficacy, ocular and dermatologic safety, and visual comfort, the Center for Environmental Therapeutics (CET) recommends the following criteria for light box selection:
- Light boxes should have been tested successfully in peer-reviewed clinical trials.
- The box should provide 10,000 lux of illumination at a comfortable sitting distance. Product specifications are often missing or unverified; illuminance can be controlled using a light meter.
- Fluorescent lamps should have a smooth diffusing screen that filters out ultraviolet (UV) rays. UV rays are harmful to the eyes and skin.
- Blue light is known to be superior to red light in managing depressive symptoms which have a seasonal pattern.
- The light should be projected downward toward the eyes at an angle to minimize aversive visual glare.
- Smaller is not better; when using a compact light box, even small head movements will take the eyes out of the therapeutic range of the light.
Risks and complications
Ultraviolet light causes progressive damage to human skin and erythema even from small doses. This is mediated by genetic damage, collagen damage, as well as destruction of vitamin A and vitamin C in the skin and free radical generation. Ultraviolet light is also known to be a factor in formation of cataracts. Ultraviolet radiation exposure is strongly linked to incidence of skin cancer.
Optical radiation of any kind with enough intensity can cause damage to the eyes and skin including photoconjunctivitis and photokeratitis. Researchers have questioned whether limiting blue light exposure could reduce the risk of age-related macular degeneration. It is reported that bright light therapy may activate the production of reproductive hormones, such as testosterone, luteinizing hormone, follicle-stimulating hormone, and estradiol.
Modern phototherapy lamps used in the treatment of seasonal affective disorder and sleep disorders either filter out or do not emit ultraviolet light and are considered safe and effective for the intended purpose, as long as photosensitizing drugs are not being taken at the same time and in the absence of any existing eye conditions. Light therapy is a mood altering treatment, and just as with drug treatments, there is a possibility of triggering a manic state from a depressive state, causing anxiety and other side effects. While these side effects are usually controllable, it is recommended that patients undertake light therapy under the supervision of an experienced clinician, rather than attempting to self-medicate.
Contraindications to light therapy for seasonal affective disorder include conditions that might render the eyes more vulnerable to phototoxicity, tendency toward mania, photosensitive skin conditions, or use of a photosensitizing herb (such as St. John's wort) or medication. Patients with porphyria should avoid most forms of light therapy. Patients on certain drugs such as methotrexate or chloroquine should use caution with light therapy as there is a chance that these drugs could cause porphyria.
Side effects of light therapy for sleep phase disorders include jumpiness or jitteriness, headache, eye irritation and nausea. Some non-depressive physical complaints, such as poor vision and skin rash or irritation, may improve with light therapy.
Many ancient cultures practiced various forms of heliotherapy, including people of Ancient Greece, Ancient Egypt, and Ancient Rome. The Inca, Assyrian and early German settlers also worshipped the sun as a health bringing deity. Indian medical literature dating to 1500 BCE describes a treatment combining herbs with natural sunlight to treat non-pigmented skin areas. Buddhist literature from about 200 CE and 10th-century Chinese documents make similar references.
The Faroese physician Niels Finsen is believed to be the father of modern phototherapy. He developed the first artificial light source for this purpose. Finsen used short wavelength light to treat lupus vulgaris, a skin infection caused by Mycobacterium tuberculosis. He thought that the beneficial effect was due to ultraviolet light killing the bacteria, but recent studies showed that his lens and filter system did not allow such short wavelengths to pass through, leading instead to the conclusion that light of approximately 400 nanometers generated reactive oxygen that would kill the bacteria. Finsen also used red light to treat smallpox lesions. He received the Nobel Prize in Physiology or Medicine in 1903. Scientific evidence for some of his treatments is lacking, and later eradication of smallpox and development of antibiotics for tuberculosis rendered light therapy obsolete for these diseases.
From the late nineteenth century until the early 1930s, light therapy was considered an effective and mainstream medical therapy in the UK for conditions such as varicose ulcer, 'sickly children' and a wide range of other conditions. Controlled trials by the medical scientist Dora Colebrook supported by the Medical Research Council, indicated that light therapy was not effective for such a wide range of conditions.
Since then a large array of treatments using controlled light have been developed. Though the popular consumer understanding of "light therapy" is associated with treating seasonal affective disorder, circadian rhythm disorders and skin conditions like psoriasis, other applications include the use of low level laser, red light, near-infrared and ultraviolet lights for pain management, hair growth, skin treatments,[which?] and accelerated wound healing.
- Lee E, Koo J, Berger T (2014-01-24). "UVB phototherapy and skin cancer risk: a review of the literature". Int. J. Dermatol. 44: 355–60. PMID 15869531. doi:10.1111/j.1365-4632.2004.02186.x.
- "Treating psoriasis: light therapy and phototherapy – National Psoriasis Foundation". Psoriasis.org. 2014-02-14. Retrieved 2014-02-18.
- Patrizi, A; Raone, B; Ravaioli, GM (5 October 2015). "Management of atopic dermatitis: safety and efficacy of phototherapy.". Clinical, cosmetic and investigational dermatology. 8: 511–20. PMC . PMID 26491366. doi:10.2147/CCID.S87987.
- Diffey BL (1980). "Ultraviolet radiation physics and the skin". Phys. Med. Biol. 25 (3): 405–26. Bibcode:1980PMB....25..405D. PMID 6996006. doi:10.1088/0031-9155/25/3/001.
- "What is Psoriasis: What Causes Psoriasis?". 29 January 2012. Retrieved 11 July 2012.
- Adauwiyah J, Suraiya HH (December 2010). "A retrospective study of narrowband-UVB phototherapy for treatment of vitiligo in Malaysian patients". Med. J. Malaysia. 65 (4): 297–99. PMID 21901949.
- Titus S, Hodge J (October 2012). "Diagnosis and treatment of acne". Am Fam Physician. 86 (8): 734–40. PMID 23062156.
- Pei S, Inamadar AC, Adya KA, Tsoukas MM (2015). "Light-based therapies in acne treatment". Indian Dermatol Online J. 6 (3): 145–57. PMC . PMID 26009707. doi:10.4103/2229-5178.156379.
- Hession MT, Markova A, Graber EM (2015). "A review of hand-held, home-use cosmetic laser and light devices". Dermatol Surg. 41 (3): 307–20. PMID 25705949. doi:10.1097/DSS.0000000000000283.
- Hamilton FL, Car J, Lyons C, Car M, Layton A, Majeed A (June 2009). "Laser and other light therapies for the treatment of acne vulgaris: systematic review". Br. J. Dermatol. 160 (6): 1273–85. PMID 19239470. doi:10.1111/j.1365-2133.2009.09047.x.
- "Light Therapy". American Cancer Society. 14 April 2011. Archived from the original on 2015-02-12. Retrieved 2013-09-08.
- Morton, C.A.; Brown, S.B.; Collins, S.; Ibbotson, S.; Jenkinson, H.; Kurwa, H.; Langmack, K.; Mckenna, K.; Moseley, H.; Pearse, A.D.; Stringer, M.; Taylor, D.K.; Wong, G.; Rhodes, L.E. (April 2002). "Guidelines for topical photodynamic therapy: report of a workshop of the British Photodermatology Group". British Journal of Dermatology. 146 (4): 552–567. doi:10.1046/j.1365-2133.2002.04719.x.
- Baron ED, Stevens SR (2003). "Phototherapy for cutaneous T-cell lymphoma". nih.gov. 16: 303–10. PMID 14686973.
- Bandow, Grace D.; Koo, John Y. M. (August 2004). "Narrow-band ultraviolet B radiation: a review of the current literature". International Journal of Dermatology. 43 (8): 555–561. PMID 15304175. doi:10.1111/j.1365-4632.2004.02032.x.
- Bouzari N, Elsaie ML, Nouri K (2012). "Laser and Light for Wound Healing Stimulation". In Nouri K. Lasers in Dermatology and Medicine. Springer London. pp. 267–75. ISBN 978-0-85729-281-0. doi:10.1007/978-0-85729-281-0_20.
- Posten W, Wrone DA, Dover JS, Arndt KA, Silapunt S, Alam M (2005). "Low-level laser therapy for wound healing: mechanism and efficacy". Dermatol Surg. 31 (3): 334–40. PMID 15841638. doi:10.1111/j.1524-4725.2005.31086.
- Arden, G. B.; Sivaprasad, S. (2012-02-03). "The pathogenesis of early retinal changes of diabetic retinopathy". Documenta Ophthalmologica. 124 (1): 15–26. ISSN 0012-4486. doi:10.1007/s10633-011-9305-y.
- Sivaprasad S, Arden G (2016). "Spare the rods and spoil the retina: revisited". Eye (Lond) (Review). 30 (2): 189–92. PMC . PMID 26656085. doi:10.1038/eye.2015.254.
- "Light Therapy – Topic Overview". WebMD. 30 June 2009. Retrieved 11 July 2012.
- Sanassi Lorraine A (2014). "Seasonal affective disorder: Is there light at the end of the tunnel?.". Journal of the American Academy of Physician Assistants. 27 (2): 18–22. doi:10.1097/01.jaa.0000442698.03223.f3.
- Thompson C, Stinson D, Smith A (September 1990). "Seasonal affective disorder and season-dependent abnormalities of melatonin suppression by light". Lancet. 336 (8717): 703–06. PMID 1975891. doi:10.1016/0140-6736(90)92202-S.
- Services, Statens beredning för medicinsk och social utvärdering (SBU); Swedish Agency for Health Technology Assessment and Assessment of Social. "Light Therapy for Depression, and Other Treatment of Seasonal Affective Disorder". www.sbu.se. Retrieved 2017-06-07.
- Crouch, David (2015-01-24). "Swedish school sheds light on dark days of winter". The Guardian. ISSN 0261-3077. Retrieved 2017-06-07.
- Benedetti F, Colombo C, Pontiggia A, Bernasconi A, Florita M, Smeraldi E, (2003) Morning light treatment hastens the antidepressant effect of citalopram: a placebo-controlled trial, J Clin Psychiatry. Jun; 64(6) 648-53.
- Prasko J (November 2008). "Bright light therapy". Neuro Endocrinol. Lett. 29 Suppl 1: 33–64. PMID 19029878.
- Terman M (December 2007). "Evolving applications of light therapy". Sleep Med Rev. 11 (6): 497–507. PMID 17964200. doi:10.1016/j.smrv.2007.06.003.
- Tuunainen, A; Kripke, DF; Endo, T (2004). Tuunainen, Arja, ed. "Light therapy for non-seasonal depression". Cochrane Database of Systematic Reviews (2): CD004050. PMID 15106233. doi:10.1002/14651858.CD004050.pub2.
- Even, C; Schröder, CM; Friedman, S; Rouillon, F (2008). "Efficacy of light therapy in nonseasonal depression: A systematic review". Journal of Affective Disorders. 108 (1–2): 11–23. PMID 17950467. doi:10.1016/j.jad.2007.09.008.
- Mårtensson B, Pettersson A, Berglund L, Ekselius L (2015). "Bright white light therapy in depression: A critical review of the evidence". J Affect Disord. 182: 1–7. PMID 25942575. doi:10.1016/j.jad.2015.04.013.
- Bjorvatn, Bjørn; Pallesen, Ståle (February 2009). "A practical approach to circadian rhythm sleep disorders". Sleep Medicine Reviews. 13 (1): 47–60. doi:10.1016/j.smrv.2008.04.009.
- Zisapel, Nava (2001). "Circadian Rhythm Sleep Disorders". CNS Drugs. 15 (4): 311–328. doi:10.2165/00023210-200115040-00005.
- Smith MR, Eastman CI (December 2008). "Night shift performance is improved by a compromise circadian phase position: study 3. Circadian phase after 7 night shifts with an intervening weekend off". Sleep. 31 (12): 1639–45. PMC . PMID 19090319.
- Brown GM, Pandi-Perumal SR, Trakht I, Cardinali DP (March 2009). "Melatonin and its relevance to jet lag". Travel Med Infect Dis. 7 (2): 69–81. PMID 19237140. doi:10.1016/j.tmaid.2008.09.004.
- Willis G. L.; Moore C.; Armstrong S. M. (2012). "A historical justification for and retrospective analysis of the systematic application of light therapy in Parkinson's disease". Reviews in the Neurosciences. 23 (2): 199–226. PMID 22499678. doi:10.1515/revneuro-2011-0072.
- Newman TB, Kuzniewicz MW, Liljestrand P, Wi S, McCulloch C, Escobar GJ (May 2009). "Numbers needed to treat with phototherapy according to American Academy of Pediatrics guidelines". Pediatrics. 123 (5): 1352–59. PMC . PMID 19403502. doi:10.1542/peds.2008-1635.
- "Phototherapy for Acne". Aetna.com. Retrieved 2015-02-25.
- Wright HR, Lack LC, Kennaway DJ (March 2004). "Differential effects of light wavelength in phase advancing the melatonin rhythm". J. Pineal Res. 36 (2): 140–44. PMID 14962066. doi:10.1046/j.1600-079X.2003.00108.x.
- Saeeduddin Ahmed; Neil L Cutter; Alfred J. Lewy; Vance K. Bauer; Robert L Sack; Mary S. Cardoza (1995). "Phase Response Curve of Low-Intensity Green Light in Winter Depressives". Sleep Research. 24: 508. doi:10.1186/1471-244X-5-42.
The magnitude of the phase shifts [using low-level green light therapy] are comparable to those obtained using high-intensity white light in winter-depressives.
- Michel A. Paul; James C. Miller; Gary Gray; Fred Buick; Sofi Blazeski; Josephine Arendt (July 2007). "Circadian Phase Delay Induced by Phototherapeutic Devices". Sleep Research. 78 (7): 645–52.
- J.J. Gooley; S.M.W. Rajaratnam; G.C. Brainard; R.E. Kronauer; C.A. Czeisler; S.W. Lockley (May 2010). "Spectral Responses of the Human Circadian System Depend on the Irradiance and Duration of Exposure to Light". Science Translational Medicine. 2 (31): 31–33. PMC . PMID 20463367. doi:10.1126/scitranslmed.3000741.
- "Light Box Selection". Center for Environmental Therapeutics. CET. Retrieved 25 May 2011.
- Glickman, G; Byrne, B; Pineda, C; Hauck, WW; Brainard, GC (Mar 15, 2006). "Light therapy for seasonal affective disorder with blue narrow-band light-emitting diodes (LEDs).". Biological Psychiatry. 59 (6): 502–07. PMID 16165105. doi:10.1016/j.biopsych.2005.07.006.
- Matsumura, Yasuhiro; Ananthaswamy, Honnavara N (March 2004). "Toxic effects of ultraviolet radiation on the skin". Toxicology and Applied Pharmacology. 195 (3): 298–308. PMID 15020192. doi:10.1016/j.taap.2003.08.019.
- Barkham. "One face, but two sides of a story". Theguardian.com. Retrieved 7 October 2014.
- Yam, Jason C. S.; Kwok, Alvin K. H. (31 May 2013). "Ultraviolet light and ocular diseases". International Ophthalmology. 34 (2): 383–400. PMID 23722672. doi:10.1007/s10792-013-9791-x.
- International Commission on Non-Ionizing Radiation, Protection. (August 2004). "Guidelines on limits of exposure to ultraviolet radiation of wavelengths between 180 nm and 400 nm (incoherent optical radiation).". Health physics. 87 (2): 171–86. PMID 15257218. doi:10.1097/00004032-200408000-00006.
- Ichihashi, M.; Ueda, M.; Budiyanto, A.; Bito, T.; Oka, M.; Fukunaga, M.; Tsuru, K.; Horikawa, T. (July 2003). "UV-induced skin damage". Toxicology. 189 (1-2): 21–39. doi:10.1016/S0300-483X(03)00150-1.
- Matsumura, Yasuhiro; Ananthaswamy, Honnavara N (March 2004). "Toxic effects of ultraviolet radiation on the skin". Toxicology and Applied Pharmacology. 195 (3): 298–308. PMID 15020192. doi:10.1016/j.taap.2003.08.019.
- Epstein, Franklin H.; Gilchrest, Barbara A.; Eller, Mark S.; Geller, Alan C.; Yaar, Mina (29 April 1999). "The Pathogenesis of Melanoma Induced by Ultraviolet Radiation". New England Journal of Medicine. 340 (17): 1341–1348. doi:10.1056/NEJM199904293401707.
- European Commission; Directorate-General for Employment, Social Affairs and Inclusion (2011), Non-binding guide to good practice for implementing Directive 2006/25/EC 'artificial optical radiation’, ISBN 978-92-79-16046-2, doi:10.2767/74218
- Glazer-Hockstein C, Dunaief JL (January 2006). "Could blue light-blocking lenses decrease the risk of age-related macular degeneration?". Retina. 26 (1): 1–4. PMID 16395131. doi:10.1097/00006982-200601000-00001.
- "Bright Light May Boost Testosterone". WebMD. Retrieved 2008-12-15.
- Danilenko KV, Samoilova EA (2007). "Stimulatory effect of morning bright light on reproductive hormones and ovulation: results of a controlled crossover trial". PLoS Clinical Trials. 2 (2): e7. PMC . PMID 17290302. doi:10.1371/journal.pctr.0020007.
- Terman M, Terman JS (August 2005). "Light therapy for seasonal and nonseasonal depression: efficacy, protocol, safety, and side effects". CNS Spectr. 10 (8): 647–63; quiz 672. PMID 16041296.
- Gagarina, AK (2007-12-08). "Light Therapy Diagnostic Indications and Contraindications". American Medical Network. Retrieved 2009-06-09.
- Westrin, Åsa; Lam, Raymond W. (October 2007). "Seasonal Affective Disorder: A Clinical Update". Annals of Clinical Psychiatry. 19 (4): 239–246. PMID 18058281. doi:10.1080/10401230701653476.
- Mayo Clinic Staff (20 March 2013). "Light Therapy. Tests and Procedures. Risks.". Mayo Clinic. Retrieved 7 February 2014.
- Roger DR (2007-12-04). "Practical aspects of light therapy". American Medical Network. Retrieved 2009-06-09.
- F. Ellinger Medical Radiation Biology Springfield 1957
- "How Finsen's light cured lupus vulgaris". Photodermatol Photoimmunol Photomed. 21: 118–24. 2014-11-12. PMID 15888127. doi:10.1111/j.1600-0781.2005.00159.x.
- "The Nobel Prize in Physiology or Medicine 1903". Nobelprize.org. Nobel Media AB. 2016-11-01. Archived from the original on 2016-10-22. Retrieved 2016-11-01.
- "Engines of our Ingenuity No. 1769: NIELS FINSEN". Retrieved 2014-04-05.
- Edwards, Martin. "Dora Colebrook and the evaluation of light therapy.". The James Lind Library. Royal College of Physicians of Edinburgh and Minervation Ltd. Retrieved 12 February 2017.
Media related to Phototherapy at Wikimedia Commons