Light therapy#Jet lag

File:Bili light with newborn.jpg (hyperbilirubinemia)]]

Exposure to UV-B light at wavelengths of 290-300 nanometers enables the body to produce vitamin D3 to treat vitamin D3 deficiency.{{Cite journal |last1=Kalajian |first1=T. A. |last2=Aldoukhi |first2=A. |last3=Veronikis |first3=A. J. |last4=Persons |first4=K. |last5=Holick |first5=M. F. |date=2017-09-13 |title=Ultraviolet B Light Emitting Diodes (LEDs) Are More Efficient and Effective in Producing Vitamin D3 in Human Skin Compared to Natural Sunlight |journal=Scientific Reports |language=en |volume=7 |issue=1 |page=11489 |doi=10.1038/s41598-017-11362-2 |pmid=28904394 |pmc=5597604 |issn=2045-2322}}

File:Blue Light acne phototherapy iClear.jpg

Light therapy treatments for the skin usually involve exposure to ultraviolet light.{{Cite web |title=PUVA therapy for skin diseases: treatment features {{!}} Heliotherapy Research Institute |url=https://heliotherapy.institute/puva-therapy/ |access-date=2022-06-01 |language=en-US}} The exposures can be to a small area of the skin or over the whole body surface, as in a tanning bed. The most common treatment is with narrowband UVB, which has a wavelength of approximately 311–313 nanometers. Full body phototherapy can be delivered at a doctor's office or at home using a large high-power UVB booth.{{cite web|url=http://www.psoriasis.org/about-psoriasis/treatments/phototherapy |title=Treating psoriasis: light therapy and phototherapy – National Psoriasis Foundation |publisher=Psoriasis.org |date=2014-02-14 |access-date=2014-02-18}} Tanning beds, however, generate mostly UVA light, and only 4% to 10% of tanning-bed light is in the UVB spectrum.

{{as of|2012}} evidence for light therapy and lasers in the treatment of acne vulgaris was not sufficient to recommend them.{{cite journal |vauthors=Titus S, Hodge J |title=Diagnosis and treatment of acne |journal=Am Fam Physician |volume=86 |issue=8 |pages=734–740 |date=October 2012 |pmid=23062156 |url=http://www.aafp.org/afp/2012/1015/p734.html}} 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.{{cite journal |vauthors=Pei S, Inamadar AC, Adya KA, Tsoukas MM |title=Light-based therapies in acne treatment |journal=Indian Dermatol Online J |volume=6 |issue=3 |pages=145–157 |year=2015 |pmid=26009707 |pmc=4439741 |doi=10.4103/2229-5178.156379 |doi-access=free }}{{cite journal |vauthors=Hession MT, Markova A, Graber EM |s2cid=39722284 |title=A review of hand-held, home-use cosmetic laser and light devices |journal=Dermatol Surg |volume=41 |issue=3 |pages=307–320 |year=2015 |pmid=25705949 |doi=10.1097/DSS.0000000000000283}} 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.{{cite journal |vauthors=Hamilton FL, Car J, Lyons C, Car M, Layton A, Majeed A |s2cid=6902995 |title=Laser and other light therapies for the treatment of acne vulgaris: systematic review |journal=Br. J. Dermatol. |volume=160 |issue=6 |pages=1273–1285|date=June 2009 |pmid=19239470 |doi=10.1111/j.1365-2133.2009.09047.x}}

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. Patients tolerate the therapy safely but, as in any therapy, there are potential adverse effects and care must be taken in its application, particularly to children.{{cite journal|last1=Patrizi|first1=A|last2=Raone|first2=B|last3=Ravaioli|first3=GM|title=Management of atopic dermatitis: safety and efficacy of phototherapy.|journal=Clinical, Cosmetic and Investigational Dermatology|date=5 October 2015|volume=8|pages=511–520|doi=10.2147/CCID.S87987|pmid=26491366|pmc=4599569|doi-access=free}} According to a study involving 21 adults with severe atopic dermatitis, narrowband UVB phototherapy administered three times per week for 12 weeks reduced atopic dermatitis severity scores by 68%. In this open study, 15 patients still experienced long-term benefits six months later.{{cite web |title=Phototherapy for Eczema: The Ultimate Guide to Using UV Light Therapy |url=https://skinsuperclear.com/eczema-phototherapy/ |website=skinsuperclear.com |date=22 March 2023 |access-date=24 March 2023}}

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.{{cite web|url=http://www.cancer.org/Treatment/TreatmentsandSideEffects/ComplementaryandAlternativeMedicine/HerbsVitaminsandMinerals/light-therapy?sitearea=ETO|title=Light Therapy|date=14 April 2011|publisher=American Cancer Society |archive-url=https://web.archive.org/web/20150212175309/http://www.cancer.org/treatment/treatmentsandsideeffects/complementaryandalternativemedicine/herbsvitaminsandminerals/light-therapy?sitearea=ETO | archive-date=2015-02-12|access-date=2013-09-08}} Photodynamic therapy (often with red light) is used to treat certain superficial non-melanoma skin cancers.{{cite journal|last1=Morton|first1=C.A.|last2=Brown|first2=S.B.|last3=Collins|first3=S.|last4=Ibbotson|first4=S.|last5=Jenkinson|first5=H.|last6=Kurwa|first6=H.|last7=Langmack|first7=K.|last8=Mckenna|first8=K.|last9=Moseley|first9=H.|last10=Pearse|first10=A.D.|last11=Stringer|first11=M.|last12=Taylor|first12=D.K.|last13=Wong|first13=G.|last14=Rhodes|first14=L.E.|s2cid=7137209|title=Guidelines for topical photodynamic therapy: report of a workshop of the British Photodermatology Group|journal=British Journal of Dermatology|date=April 2002|volume=146|issue=4|pages=552–567|doi=10.1046/j.1365-2133.2002.04719.x|pmid=11966684}}

{{See also|Goeckerman therapy}}

For psoriasis, UVB phototherapy has been shown to be effective.{{cite journal | author = Diffey BL | year = 1980 | title = Ultraviolet radiation physics and the skin | journal = Phys. Med. Biol. | volume = 25 | issue = 3| pages = 405–426 | doi = 10.1088/0031-9155/25/3/001 | pmid = 6996006 | bibcode = 1980PMB....25..405D| s2cid = 250744277 }} A feature of psoriasis is localized inflammation mediated by the immune system.{{cite web|url=http://www.medicalbug.com/what-is-psoriasis-what-causes-psoriasis/|title=What is Psoriasis: What Causes Psoriasis?|date=29 January 2012|access-date=11 July 2012}} Ultraviolet radiation is known to suppress the immune system and reduce inflammatory responses. Light therapy for skin conditions like psoriasis usually use 313 nanometer UVB though it may use UVA (315–400 nm wavelength) or a broader spectrum UVB (280–315 nm wavelength). UVA 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.

About 1% of the human population has vitiligo which causes painless distinct light-colored patches of the skin on the face, hands, and legs. Phototherapy is an effective treatment because it forces skin cells to manufacture melanin to protect the body from UV damage. Prescribed treatment is generally 3 times a week in a clinic or daily at home. About 1 month usually results in re-pigmentation in the face and neck, and 2–4 months in the hands and legs. Narrowband UVB is more suitable to the face and neck and PUVA is more effective at the hands and legs.{{cite journal |last1=Bae |first1=Jung Min |last2=Jung |first2=Han Mi |last3=Hong |first3=Bo Young |last4=Lee |first4=Joo Hee |last5=Choi |first5=Won Joon |last6=Lee |first6=Ji Hae |last7=Kim |first7=Gyong Moon |title=Phototherapy for Vitiligo |journal=JAMA Dermatology |date=1 July 2017 |volume=153 |issue=7 |pages=666–674 |doi=10.1001/jamadermatol.2017.0002 |pmid=28355423 |pmc=5817459}}

Some types of phototherapy may be effective in the treatment of polymorphous light eruption, cutaneous T-cell lymphoma{{Cite journal|title=Phototherapy for cutaneous T-cell lymphoma|vauthors=Baron ED, Stevens SR|journal= Dermatologic Therapy|pmid=14686973|volume=16|issue=4|year=2003|pages=303–310|doi=10.1111/j.1396-0296.2003.01642.x|s2cid=33047908}} and lichen planus. Narrowband UVB between 311 and 313 nanometers is the most common treatment.{{cite journal|last1=Bandow|first1=Grace D.|last2=Koo|first2=John Y. M.|title=Narrow-band ultraviolet B radiation: a review of the current literature|journal=International Journal of Dermatology|date=August 2004|volume=43|issue=8|pages=555–561|doi=10.1111/j.1365-4632.2004.02032.x|pmid=15304175|s2cid=27388121}}

There is preliminary evidence that light therapy is an effective treatment for diabetic retinopathy and diabetic macular oedema.{{Cite journal|last1=Arden|first1=G. B.|last2=Sivaprasad|first2=S.|s2cid=25514638|date=2012-02-03|title=The pathogenesis of early retinal changes of diabetic retinopathy|journal=Documenta Ophthalmologica|volume=124|issue=1|pages=15–26|doi=10.1007/s10633-011-9305-y|pmid=22302291|issn=0012-4486}}{{cite journal |vauthors=Sivaprasad S, Arden G |title=Spare the rods and spoil the retina: revisited |journal=Eye (Lond) |volume=30 |issue=2 |pages=189–192 |year=2016 |pmid=26656085 |doi=10.1038/eye.2015.254 |type=Review |pmc=4763134}}

{{Main|Seasonal affective disorder}}

The effectiveness of light therapy for treating seasonal affective disorder (SAD) may be linked to reduced sunlight exposure in the winter months. Light resets the body's internal clock.{{cite web|url=http://www.webmd.com/depression/tc/light-therapy-topic-overview|title=Light Therapy – Topic Overview|date=30 June 2009|publisher=WebMD|access-date=11 July 2012}} Studies show that light therapy helps reduce the debilitating depressive symptoms 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 with minimal side effects.{{cite journal | author = Sanassi Lorraine A | year = 2014 | title = Seasonal affective disorder: Is there light at the end of the tunnel?. | journal = Journal of the American Academy of Physician Assistants | volume = 27 | issue = 2| pages = 18–22 | doi=10.1097/01.jaa.0000442698.03223.f3| pmid = 24394440 | s2cid = 45234549| doi-access = free }} Two methods of light therapy, bright light and dawn simulation, have similar success rates in the treatment of SAD.{{Cite journal|last1=Danilenko|first1=K.V.|last2=Ivanova|first2=I.A.|date=July 2015|title=Dawn simulation vs. bright light in seasonal affective disorder: Treatment effects and subjective preference|url=|journal=Journal of Affective Disorders|language=en|volume=180|pages=87–89|doi=10.1016/j.jad.2015.03.055|pmid=25885065 }}

It is possible that response to light therapy for SAD could be season dependent.{{cite journal |vauthors=Thompson C, Stinson D, Smith A |s2cid=34280446 |title=Seasonal affective disorder and season-dependent abnormalities of melatonin suppression by light |journal=Lancet |volume=336 |issue=8717 |pages=703–706 |date=September 1990 |pmid=1975891 |doi=10.1016/0140-6736(90)92202-S}} Morning therapy has provided the best results because light in the early morning aids in regulating the circadian rhythm. People affected by SAD often have low energy, tend to eat more carbohydrates and sleep longer, but symptoms can vary between people.{{cite web |last1=Doyle |first1=Ashley |title=Light Therapy: Does It Work and Can It Help You? |url=https://savvysleeper.org/can-light-therapy-help-you-sleep/ |website=Savvysleeper |access-date=19 July 2019}}

A Cochrane review conducted in 2019 states the evidence that light therapy's effectiveness as a treatment for the prevention of seasonal affective disorder is limited, although the risk of adverse effects are minimal. Therefore, the decision to use light therapy should be based on a person's preference of treatment.{{Cite journal |doi = 10.1002/14651858.CD011269.pub3|pmid = 30883670|pmc = 6422319|title = Light therapy for preventing seasonal affective disorder|year = 2019|last1 = Nussbaumer-Streit|first1 = Barbara|last2 = Forneris|first2 = Catherine A.|last3 = Morgan|first3 = Laura C.|last4 = Van Noord|first4 = Megan G.|last5 = Gaynes|first5 = Bradley N.|last6 = Greenblatt|first6 = Amy|last7 = Wipplinger|first7 = Jörg|last8 = Lux|first8 = Linda J.|last9 = Winkler|first9 = Dietmar|last10 = Gartlehner|first10 = Gerald|journal = Cochrane Database of Systematic Reviews|volume = 3| issue=4 |pages = CD011269}}

Light therapy has also been suggested in the treatment of non-seasonal depression and other psychiatric mood disturbances, including major depressive disorder,{{cite journal |last1=Benedetti |first1=Francesco |last2=Colombo |first2=Cristina |last3=Pontiggia |first3=Adriana |last4=Bernasconi |first4=Alessandro |last5=Florita |first5=Marcello |last6=Smeraldi |first6=Enrico |s2cid=40483934 |title=Morning light treatment hastens the antidepressant effect of citalopram: a placebo-controlled trial. |journal=The Journal of Clinical Psychiatry |date=June 2003 |volume=64 |issue=6 |pages=648–653 |pmid=12823078 |doi=10.4088/JCP.v64n0605}}{{Cite journal|last1=Tuunainen|first1=Arja|last2=Kripke|first2=Daniel F|last3=Endo|first3=Takuro|date=2004-04-19|title=Light therapy for non-seasonal depression|journal=The Cochrane Database of Systematic Reviews|volume=2004|issue=2|pages=CD004050|doi=10.1002/14651858.CD004050.pub2|issn=1469-493X|pmc=6669243|pmid=15106233}} bipolar disorder and postpartum depression.{{cite journal |author=Prasko J |title=Bright light therapy |journal=Neuro Endocrinol. Lett. |volume=29 |pages=33–64 |date=November 2008 |issue=Suppl 1 |pmid=19029878}}{{cite journal |author=Terman M |title=Evolving applications of light therapy |journal=Sleep Med Rev |volume=11 |issue=6 |pages=497–507 |date=December 2007 |pmid=17964200 |doi=10.1016/j.smrv.2007.06.003|s2cid=2054580 }} A meta-analysis by the Cochrane Collaboration concluded that "for patients suffering from non-seasonal depression, light therapy offers modest though promising antidepressive efficacy."{{cite journal |last1=Tuunainen |first1=Arja |last2=Kripke |first2=Daniel F |last3=Endo |first3=Takuro |title=Light therapy for non-seasonal depression |journal=Cochrane Database of Systematic Reviews |issue=2 |date=19 April 2004 |volume=2004 |pages=CD004050 |pmid=15106233 |pmc=6669243 |doi=10.1002/14651858.CD004050.pub2}} 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."{{cite journal|pmid=17950467|year=2008|last1=Even|first1=C|last2=Schröder|first2=CM|last3=Friedman|first3=S|last4=Rouillon|first4=F|title=Efficacy of light therapy in nonseasonal depression: A systematic review|volume=108|issue=1–2|pages=11–23|doi=10.1016/j.jad.2007.09.008|journal=Journal of Affective Disorders}} A 2015 review found that supporting evidence for light therapy was limited due to serious methodological flaws.{{cite journal |author=Mårtensson B |author2=Pettersson A |author3=Berglund L |author4=Ekselius L |title=Bright white light therapy in depression: A critical review of the evidence |journal=J Affect Disord |volume=182 |pages=1–7 |year=2015 |pmid=25942575 |doi=10.1016/j.jad.2015.04.013}}

A 2016 meta-analysis showed that bright light therapy appeared to be efficacious, particularly when administered for 2–5 weeks' duration and as monotherapy.Al-Karawi D, Jubair L. [https://pubmed.ncbi.nlm.nih.gov/27011361/ "Bright light therapy for nonseasonal depression: Meta-analysis of clinical trials".] J Affect Disord. 2016 Jul 1;198:64–71. {{doi|10.1016/j.jad.2016.03.016}}. Epub 2016 Mar 15. {{PMID|27011361}}.

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.{{cite journal|last1=Bjorvatn|first1=Bjørn|last2=Pallesen|first2=Ståle|title=A practical approach to circadian rhythm sleep disorders|journal=Sleep Medicine Reviews|date=February 2009|volume=13|issue=1|pages=47–60|doi=10.1016/j.smrv.2008.04.009|pmid=18845459}} Use upon awakening may also be effective for non-24-hour sleep–wake disorder.{{cite journal|last1=Zisapel|first1=Nava|s2cid=34990596|title=Circadian Rhythm Sleep Disorders|journal=CNS Drugs|date=2001|volume=15|issue=4|pages=311–328|doi=10.2165/00023210-200115040-00005|pmid=11463135}} 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.

{{Main|Circadian rhythm sleep disorder}}

Source:{{Cite journal|last1=Dodson|first1=Ehren R.|last2=Zee|first2=Phyllis C|date=December 2010|title=Therapeutics for Circadian Rhythm Sleep Disorders|journal=Sleep Medicine Clinics|volume=5|issue=4|pages=701–715|doi=10.1016/j.jsmc.2010.08.001|issn=1556-407X|pmc=3020104|pmid=21243069}}

Light therapy has been tested for individuals with shift work sleep disorder and for jet lag.{{cite journal |vauthors=Brown GM, Pandi-Perumal SR, Trakht I, Cardinali DP |title=Melatonin and its relevance to jet lag |journal=Travel Med Infect Dis |volume=7 |issue=2 |pages=69–81 |date=March 2009 |pmid=19237140 |doi=10.1016/j.tmaid.2008.09.004}}{{cite book |doi=10.1016/B978-0-12-378610-4.00285-0 |chapter=Light and Melatonin Treatment for Jet Lag Disorder |title=Encyclopedia of Sleep |pages=74–80 |year=2013 |last1=Crowley |first1=S.J. |last2=Eastman |first2=C.I. |isbn=978-0-12-378611-1}}

Light therapy has been trialed in treating sleep disorders experienced by patients with Parkinson's disease.{{cite journal |author1=Willis G. L. |author2=Moore C. |author3=Armstrong S. M. |s2cid=37717110 | year = 2012 | title = A historical justification for and retrospective analysis of the systematic application of light therapy in Parkinson's disease | journal = Reviews in the Neurosciences | volume = 23 | issue = 2| pages = 199–226 | pmid = 22499678 | doi=10.1515/revneuro-2011-0072}}

Studies have shown that daytime and evening light therapy for nursing home patients with Alzheimer's disease, who often struggle with agitation and fragmented wake/rest cycles effectively led to more consolidated sleep and an increase in circadian rhythm stability.{{cite journal |title=Bright light treatment of behavioral and sleep disturbances in patients with Alzheimer's disease |journal=American Journal of Psychiatry |date=August 1992 |volume=149 |issue=8 |pages=1028–1032 |doi=10.1176/ajp.149.8.1028 |pmid=1353313 |last1=Satlin |first1=A. |last2=Volicer |first2=L. |last3=Ross |first3=V. |last4=Herz |first4=L. |last5=Campbell |first5=S.}}{{cite journal |last1=Ancoli-Israel |first1=Sonia |last2=Gehrman |first2=Philip |last3=Martin |first3=Jennifer L. |last4=Shochat |first4=Tamar |last5=Marler |first5=Matthew |last6=Corey-Bloom |first6=Jody |last7=Levi |first7=Leah |title=Increased Light Exposure Consolidates Sleep and Strengthens Circadian Rhythms in Severe Alzheimer's Disease Patients |journal=Behavioral Sleep Medicine |date=February 2003 |volume=1 |issue=1 |pages=22–36 |doi=10.1207/s15402010bsm0101_4 |pmid=15600135 |s2cid=39597697}}{{cite journal |last1=Hanford |first1=Nicholas |last2=Figueiro |first2=Mariana |title=Light Therapy and Alzheimer's Disease and Related Dementia: Past, Present, and Future |journal=Journal of Alzheimer's Disease |date=21 January 2013 |volume=33 |issue=4 |pages=913–922 |doi=10.3233/jad-2012-121645 |pmid=23099814 |pmc=3553247}}

{{Further|Neonatal jaundice|Bili light}}

File:Jaundice phototherapy.jpgLight therapy is used to treat cases of neonatal jaundice.{{cite journal |vauthors=Newman TB, Kuzniewicz MW, Liljestrand P, Wi S, McCulloch C, Escobar GJ |title=Numbers needed to treat with phototherapy according to American Academy of Pediatrics guidelines |journal=Pediatrics |volume=123 |issue=5 |pages=1352–1359 |date=May 2009 |pmid=19403502 |doi=10.1542/peds.2008-1635 |pmc=2843697}} Bilirubin, a yellow pigment normally formed in the liver during the breakdown of old red blood cells, cannot always be effectively cleared by a neonate's liver causing neonatal jaundice. Accumulation of excess bilirubin can cause central nervous system damage, and so this buildup of bilirubin must be treated. Phototherapy uses the energy from light to isomerize the bilirubin and consequently transform it into compounds that the newborn can excrete via urine and stools. Bilirubin is most successful absorbing light in the blue region of the visible light spectrum, which falls between 460 and 490 nm.{{cite book |doi=10.1007/1-4020-2885-7_13 |chapter=Phototherapy of Neonatal Jaundice |title=The Science of Phototherapy: An Introduction |pages=329–335 |year=2005 |isbn=978-1-4020-2883-0 |last1=Grossweiner |first1=Leonard I. |last2=Grossweiner |first2=James B. |last3=Gerald Rogers |first3=B. H. |chapter-url=http://real.mtak.hu/5273/1/1141092.PDF}} Therefore, light therapy technologies that utilize these blue wavelengths are the most successful at isomerizing bilirubin.{{cite journal |title=Phototherapy in neonatal jaundice. |journal=BMJ |date=8 April 1972 |volume=2 |issue=5805 |pages=62–63 |doi=10.1136/bmj.2.5805.62-a |s2cid=43085146 |doi-access=free}}

{{Main|Photodynamic therapy}}

Photodynamic therapy (PDT) is a form of phototherapy using nontoxic light-sensitive compounds (photosensitizers) that are exposed selectively to light at a controlled wavelength, laser intensity, and irradiation time, whereupon they generate toxic reactive oxygen species (ROS) that target malignant and other diseased cells. Oxygen is thus required for activity, lowering efficacy in highly developed tumors and other hypoxic environments. Selective apoptosis of diseased cells is difficult due to the radical nature of ROS, but may be controlled for through membrane potential and other cell-type specific properties'{{Cite journal |last1=Nie |first1=Xiaolin |last2=Jiang |first2=Chenyu |last3=Wu |first3=Shuanglin |last4=Chen |first4=Wangbingfei |last5=Lv |first5=Pengfei |last6=Wang |first6=Qingqing |last7=Liu |first7=Jingyan |last8=Narh |first8=Christopher |last9=Cao |first9=Xiuming |last10=Ghiladi |first10=Reza A. |last11=Wei |first11=Qufu |title=Carbon quantum dots: A bright future as photosensitizers for in vitro antibacterial photodynamic inactivation |url= |journal=Journal of Photochemistry and Photobiology B: Biology |year=2020 |language=en |volume=206 |page=111864 |doi=10.1016/j.jphotobiol.2020.111864|pmid=32247250 |bibcode=2020JPPB..20611864N |s2cid=214794593 }} effects on permeability or through photoimmunotherapy. In developing any phototherapeutic agent, the phototoxicity of the treatment wavelength should be considered.

Various cancer treatments utilizing PDT have been approved by the FDA. Treatments are available for actinic keratosis (blue light with aminolevulinic acid), cutaneous T-cell lymphoma, Barrett esophagus, basal cell skin cancer, esophageal cancer, non-small cell lung cancer, and squamous cell skin cancer (Stage 0). Photosensitizing agents clinically-approved or undergoing clinical trials for the treatment of cancers include Photofrin, Temoporfin, Motexafin lutetium, Palladium bacteriopheophorbide, Purlytin, and Talaporfin. Verteporfin is approved to treat eye conditions such as macular degeneration, myopia, and ocular histoplasmosis.{{Cite journal |last1=Baskaran |first1=Rengarajan |last2=Lee |first2=Junghan |last3=Yang |first3=Su-Geun |date=2018 |title=Clinical development of photodynamic agents and therapeutic applications |journal=Biomaterials Research |volume=22 |page=25 |doi=10.1186/s40824-018-0140-z |issn=1226-4601 |pmc=6158913 |pmid=30275968 |doi-access=free }} Third-generation photosensitizers are currently in development, but none are yet approved for clinical trials.

PDT may also be utilized to treat multidrug-resistant skin, wound, or other superficial infections. This is known as antimicrobial photodynamic therapy (aPDT) or photodynamic inactivation (PDI). aPDT has been observed to be effective against both gram-positive and gram-negative bacteria such as Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Mycobacterium. aPDT has shown lowered efficacy on some other bacterial species, such as Klebsiella pneumoniae and Acinetobacter baumannii. This is likely due to factors such as cell wall thickness and membrane potential. Many studies utilizing aPDT focus on the application of the photosensitizer through leakage from a hydrogel, which has been found to increase wound healing speed of skin infections{{Cite journal |last1=Xu |first1=Yinglin |last2=Chen |first2=Haolin |last3=Fang |first3=Yifen |last4=Wu |first4=Jun |title=Hydrogel Combined with Phototherapy in Wound Healing |url=|journal=Advanced Healthcare Materials |year=2022 |language=en |volume=11 |issue=16 |page=2200494 |doi=10.1002/adhm.202200494 |pmid=35751637 |s2cid=250021788 |issn=2192-2640}}{{Cite journal |last1=Ding |first1=Qiuyue |last2=Sun |first2=Tingfang |last3=Su |first3=Weijie |last4=Jing |first4=Xirui |last5=Ye |first5=Bing |last6=Su |first6=Yanlin |last7=Zeng |first7=Lian |last8=Qu |first8=Yanzhen |last9=Yang |first9=Xu |last10=Wu |first10=Yuzhou |last11=Luo |first11=Zhiqiang |last12=Guo |first12=Xiaodong |title=Bioinspired Multifunctional Black Phosphorus Hydrogel with Antibacterial and Antioxidant Properties: A Stepwise Countermeasure for Diabetic Skin Wound Healing |url=|journal=Advanced Healthcare Materials |year=2022 |language=en |volume=11 |issue=12 |page=2102791 |doi=10.1002/adhm.202102791 |pmid=35182097 |s2cid=246974402 |issn=2192-2640}} through the upregulation of vascular endothelial growth factor (VEGF) and hypoxia inducible factor (HIF).{{Cite journal |last1=Zhang |first1=Xingyu |last2=Zhang |first2=Guannan |last3=Zhang |first3=Hongyu |last4=Liu |first4=Xiaoping |last5=Shi |first5=Jing |last6=Shi |first6=Huixian |last7=Yao |first7=Xiaohong |last8=Chu |first8=Paul K. |last9=Zhang |first9=Xiangyu |title=A bifunctional hydrogel incorporated with CuS@MoS2 microspheres for disinfection and improved wound healing |url= |journal=Chemical Engineering Journal |year=2020 |language=en |volume=382 |page=122849 |doi=10.1016/j.cej.2019.122849|s2cid=203938686 }} This controlled leakage allows for prolonged but limited generation of ROS, lowering the impact on human cell viability due to ROS cytotoxicity. It is unlikely for drug resistance to photosensitizers to form due to the nontoxic nature of the photosensitizer itself as well as the ROS generation mechanism of action, which cannot be prevented outside of hypoxic environments. Certain dental infections (peri-implantitis, periodontitis) are more difficult to treat with PDT as opposed to photothermal therapy due to the requirement of oxygen, though a significant response is still observed.{{Cite journal |last1=Shim |first1=Sang Ho |last2=Lee |first2=Si Young |last3=Lee |first3=Jong-Bin |last4=Chang |first4=Beom-Seok |last5=Lee |first5=Jae-Kwan |last6=Um |first6=Heung-Sik |title=Antimicrobial photothermal therapy using diode laser with indocyanine green on Streptococcus gordonii biofilm attached to zirconia surface |url= |journal=Photodiagnosis and Photodynamic Therapy |year=2022 |language=en |volume=38 |page=102767 |doi=10.1016/j.pdpdt.2022.102767|pmid=35182778 |s2cid=246926124 }}{{Cite journal |last1=Böcher |first1=Sarah |last2=Wenzler |first2=Johannes-Simon |last3=Falk |first3=Wolfgang |last4=Braun |first4=Andreas |title=Comparison of different laser-based photochemical systems for periodontal treatment |url= |journal=Photodiagnosis and Photodynamic Therapy |year=2019 |language=en |volume=27 |pages=433–439 |doi=10.1016/j.pdpdt.2019.06.009|pmid=31319164 |s2cid=197663815 }}{{Cite journal |last1=Fekrazad |first1=Reza |last2=Khoei |first2=Farzaneh |last3=Bahador |first3=Abbas |last4=Hakimiha |first4=Neda |title=Comparison of different modes of photo-activated disinfection against Porphyromonas gingivalis: An in vitro study |url= |journal=Photodiagnosis and Photodynamic Therapy |year=2020 |language=en |volume=32 |page=101951 |doi=10.1016/j.pdpdt.2020.101951|pmid=32818643 |s2cid=221221714 }}

Increased antimicrobial activity and wound healing speeds are typically observed when PDT is combined with photothermal therapy in photodynamic/photothermal combination therapy.

{{Main articles|Photothermal therapy}}

Photothermal therapy (PTT) is a form of phototherapy that uses non-toxic compounds called photothermal agents (PTA) that, when irradiated at a certain wavelength of light, converts the light energy directly to heat energy. The photothermal conversion efficiency determines the amount of light converted to heat, which can dictate the necessary irradiation time and/or laser intensity for treatments. Typically PTT treatments use wavelengths in the near-infrared (NIR) spectra, which can be further divided into NIR-I (760-900 nm), NIR-II (900-1880 nm), and NIR-III (2080-2340 nm) windows.{{Cite journal |last1=Feng |first1=Zhe |last2=Tang |first2=Tao |last3=Wu |first3=Tianxiang |last4=Yu |first4=Xiaoming |last5=Zhang |first5=Yuhuang |last6=Wang |first6=Meng |last7=Zheng |first7=Junyan |last8=Ying |first8=Yanyun |last9=Chen |first9=Siyi |last10=Zhou |first10=Jing |last11=Fan |first11=Xiaoxiao |last12=Zhang |first12=Dan |last13=Li |first13=Shengliang |last14=Zhang |first14=Mingxi |last15=Qian |first15=Jun |date=2021-09-24 |title=Perfecting and extending the near-infrared imaging window |journal=Light: Science & Applications |language=en |volume=10 |issue=1 |page=197 |doi=10.1038/s41377-021-00628-0 |issn=2047-7538 |pmc=8463572 |pmid=34561416|bibcode=2021LSA....10..197F }} Wavelengths in these regions are typically less phototoxic than UV or high-energy visible light. In addition, NIR-II wavelengths have been observed to show deeper penetration than NIR-I wavelengths, allowing for treatment of deeper wounds, infections, and cancers. Important considerations for the development of a PTA include photothermal conversion efficiency, phototoxicity, laser intensity, irradiation time, and the temperature at which human cell viability is impaired (around 46-60 °C).{{Cite journal |last1=Leber |first1=Bettina |last2=Mayrhauser |first2=Ursula |last3=Leopold |first3=Barbara |last4=Koestenbauer |first4=Sonja |last5=Tscheliessnigg |first5=Karlheinz |last6=Stadlbauer |first6=Vanessa |last7=Stiegler |first7=Philipp |title=Impact of temperature on cell death in a cell-culture model of hepatocellular carcinoma |journal=Anticancer Research |year=2012 |volume=32 |issue=3 |pages=915–921 |issn=1791-7530 |pmid=22399612 }} Currently, the only FDA-approved photothermal agent is indocyanine green which is active against both tumor and bacterial cells.{{Cite journal |last1=Li |first1=Xingde |last2=Beauvoit |first2=Bertrand |last3=White |first3=Renita |last4=Nioka |first4=Shoko |last5=Chance |first5=Britton |last6=Yodh |first6=Arjun G. |editor-first1=Britton |editor-first2=Robert R. |editor-last1=Chance |editor-last2=Alfano |date=1995-05-30 |title=Tumor localization using fluorescence of indocyanine green (ICG) in rat models |url=https://www.spiedigitallibrary.org/conference-proceedings-of-spie/2389/0000/Tumor-localization-using-fluorescence-of-indocyanine-green-ICG-in-rat/10.1117/12.210021.full |journal=Optical Tomography, Photon Migration, and Spectroscopy of Tissue and Model Media: Theory, Human Studies, and Instrumentation |publisher=SPIE |volume=2389 |pages=789–797 |doi=10.1117/12.210021|bibcode=1995SPIE.2389..789L |s2cid=93116083 }}

PTT is less selective than photodynamic therapy (PDT, see above) due to its heat-based mechanism of action, but also less likely to promote drug resistance than most, if not all, currently developed treatments. In addition, PTT can be used in hypoxic environments and on deeper wounds, infections, and tumors than PDT due to the higher wavelength of light. Due to PTT activity in hypoxic environments, it may be also used on more developed tumors than PDT. Low-temperature PTT (≤ 45 °C) for treatment of infections is also a possibility when combined with an antibiotic compound due to heat's proportionality with membrane permeability - a hotter environment causes heightened membrane permeability, which thus allows the drug into the cell.{{Cite journal |last1=Blicher |first1=Andreas |last2=Wodzinska |first2=Katarzyna |last3=Fidorra |first3=Matthias |last4=Winterhalter |first4=Mathias |last5=Heimburg |first5=Thomas |date=2009-06-03 |title=The Temperature Dependence of Lipid Membrane Permeability, its Quantized Nature, and the Influence of Anesthetics |journal=Biophysical Journal |volume=96 |issue=11 |pages=4581–4591 |doi=10.1016/j.bpj.2009.01.062 |issn=0006-3495 |pmc=2711498 |pmid=19486680|arxiv=0807.4825 |bibcode=2009BpJ....96.4581B }} This would reduce/eliminate the impact on human cell viability, and aiding in antibiotic accumulation within the target cell may assist in restoring activity in antibiotics that pathogens had developed resistance to.

PTT is typically seen to have improved antimicrobial and wound healing activity when combined with an additional mechanism of action through PDT or added antibiotic compounds in the application.

{{See also|Combined photothermal and photodynamic therapy}}

File:Light therapy lamp and sunlight.jpg

{{Redirect|Light box||Lightbox (disambiguation)}}

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.{{cite journal |last1=Lazzerini Ospri |first1=Lorenzo |last2=Prusky |first2=Glen |last3=Hattar |first3=Samer |title=Mood, the Circadian System, and Melanopsin Retinal Ganglion Cells |journal=Annual Review of Neuroscience |date=25 July 2017 |volume=40 |issue=1 |pages=539–556 |doi=10.1146/annurev-neuro-072116-031324 |pmid=28525301 |pmc=5654534}} To some degree, the reverse is true for serotonin,{{cite journal |last1=Harrison |first1=S. J. |last2=Tyrer |first2=A. E. |last3=Levitan |first3=R. D. |last4=Xu |first4=X. |last5=Houle |first5=S. |last6=Wilson |first6=A. A. |last7=Nobrega |first7=J. N. |last8=Rusjan |first8=P. M. |last9=Meyer |first9=J. H. |title=Light therapy and serotonin transporter binding in the anterior cingulate and prefrontal cortex |journal=Acta Psychiatrica Scandinavica |date=November 2015 |volume=132 |issue=5 |pages=379–388 |doi=10.1111/acps.12424 |pmid=25891484 |pmc=4942271}} 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.{{cite journal |last1=Wu |first1=Mann-Chian |last2=Sung |first2=Huei-Chuan |last3=Lee |first3=Wen-Li |last4=Smith |first4=Graeme D |title=The effects of light therapy on depression and sleep disruption in older adults in a long-term care facility |journal=International Journal of Nursing Practice |date=October 2015 |volume=21 |issue=5 |pages=653–659 |doi=10.1111/ijn.12307 |pmid=24750268}}

Light therapy uses either a light box which emits up to 10,000 lux of light at a specified distance,{{efn|Lux measures the amount of illumination in a square meter. The distance affects how much area the light is spread over.}} 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.{{cite journal |vauthors=Wright HR, Lack LC, Kennaway DJ |s2cid=400498 |title=Differential effects of light wavelength in phase advancing the melatonin rhythm |journal=J. Pineal Res. |volume=36 |issue=2 |pages=140–44 |date=March 2004 |pmid=14962066 |doi=10.1046/j.1600-079X.2003.00108.x}} 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,{{cite journal |year=1995 |title=Phase Response Curve of Low-Intensity Green Light in Winter Depressives |volume=24 |page=508 |journal=Sleep Research |quote=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. |author1=Saeeduddin Ahmed |author2=Neil L Cutter |author3=Alfred J. Lewy |author4=Vance K. Bauer |author5=Robert L Sack |author6=Mary S. Cardoza |doi=10.1186/1471-244X-5-42|pmid=16283926 |pmc=1309618 |doi-access=free }}{{cite journal |date=July 2007 |title=Circadian Phase Delay Induced by Phototherapeutic Devices |volume=78 |issue=7 |pages=645–52 |journal=Sleep Research |url=http://www.ingentaconnect.com/content/asma/asem/2007/00000078/00000007/art00001 |author1=Michel A. Paul |author2=James C. Miller |author3=Gary Gray |author4=Fred Buick |author5=Sofi Blazeski |author6=Josephine Arendt}} 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.{{cite journal |author1=J.J. Gooley |author2=S.M.W. Rajaratnam |author3=G.C. Brainard |author4=R.E. Kronauer |author5=C.A. Czeisler |author6=S.W. Lockley |title=Spectral Responses of the Human Circadian System Depend on the Irradiance and Duration of Exposure to Light |journal=Science Translational Medicine |volume=2 |issue=31 |pages=31–33 |date=May 2010 |doi=10.1126/scitranslmed.3000741 |pmid=20463367 |pmc=4414925}}

Ultraviolet light causes progressive damage to human skin and erythema even from small doses.{{cite journal|last1=Matsumura|first1=Yasuhiro|last2=Ananthaswamy|first2=Honnavara N|title=Toxic effects of ultraviolet radiation on the skin|journal=Toxicology and Applied Pharmacology|date=March 2004|volume=195|issue=3|pages=298–308|doi=10.1016/j.taap.2003.08.019|pmid=15020192|bibcode=2004ToxAP.195..298M }}{{cite web|last1=Barkham|title=One face, but two sides of a story|date=5 June 2012|url=https://www.theguardian.com/society/shortcuts/2012/jun/05/face-shows-damage-from-sun|publisher=Theguardian.com|access-date=7 October 2014}} 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.{{citation needed|date=January 2013}} Ultraviolet light is also known to be a factor in formation of cataracts.{{cite journal|last1=Yam|first1=Jason C. S.|last2=Kwok|first2=Alvin K. H.|s2cid=33503388|title=Ultraviolet light and ocular diseases|journal=International Ophthalmology|date=31 May 2013|volume=34|issue=2|pages=383–400|doi=10.1007/s10792-013-9791-x|pmid=23722672}}{{cite journal|last1=International Commission on Non-Ionizing Radiation|first1=Protection.|s2cid=34605136|title=Guidelines on limits of exposure to ultraviolet radiation of wavelengths between 180 nm and 400 nm (incoherent optical radiation).|journal=Health Physics|date=August 2004|volume=87|issue=2|pages=171–86|pmid=15257218|doi=10.1097/00004032-200408000-00006|bibcode=2004HeaPh..87..171. }} Ultraviolet radiation exposure is strongly linked to incidence of skin cancer.{{cite journal|last1=Ichihashi|first1=M.|last2=Ueda|first2=M.|last3=Budiyanto|first3=A.|last4=Bito|first4=T.|last5=Oka|first5=M.|last6=Fukunaga|first6=M.|last7=Tsuru|first7=K.|last8=Horikawa|first8=T.|title=UV-induced skin damage|journal=Toxicology|date=July 2003|volume=189|issue=1–2|pages=21–39|doi=10.1016/S0300-483X(03)00150-1|pmid=12821280|bibcode=2003Toxgy.189...21I }}{{cite journal |last1=Epstein |first1=Franklin H. |last2=Gilchrest |first2=Barbara A. |last3=Eller |first3=Mark S. |last4=Geller |first4=Alan C. |last5=Yaar |first5=Mina |title=The Pathogenesis of Melanoma Induced by Ultraviolet Radiation |journal=New England Journal of Medicine |date=29 April 1999 |volume=340 |issue=17 |pages=1341–8 |doi=10.1056/NEJM199904293401707 |pmid=10219070}}

Optical radiation of any kind with enough intensity can cause damage to the eyes and skin including photoconjunctivitis and photokeratitis.{{Citation |title=Non-binding guide to good practice for implementing Directive 2006/25/EC 'artificial optical radiation' |year=2011 |author1=European Commission |author2=Directorate-General for Employment, Social Affairs and Inclusion |doi=10.2767/74218 |isbn=978-92-79-16046-2}} Researchers have questioned whether limiting blue light exposure could reduce the risk of age-related macular degeneration.{{cite journal |vauthors=Glazer-Hockstein C, Dunaief JL |s2cid=29045585 |title=Could blue light-blocking lenses decrease the risk of age-related macular degeneration? |journal=Retina |volume=26 |issue=1 |pages=1–4 |date=January 2006 |pmid=16395131 |doi=10.1097/00006982-200601000-00001}} According to the American Academy of Ophthalmology, there is no scientific evidence showing that exposure to blue light emitting devices result in eye damage.{{cite web |author-link=American Academy of Ophthalmology|last1=American Academy of Ophthalmology|title=Should You Be Worried About Blue Light? |url=https://www.aao.org/eye-health/tips-prevention/should-you-be-worried-about-blue-light |website=American Academy of Ophthalmology |access-date=29 December 2020}} According to Harriet Hall, blue light exposure is reported to suppress the production of melatonin, which affects our body's circadian rhythm and can decrease sleep quality.{{cite web |author-link=Harriet Hall|last1=Hall |first1=Harriet |title=Blue light |url=https://sciencebasedmedicine.org/blue-light/ |website=Science-based Medicine |date=December 2020 |access-date=29 December 2020}} It is reported that, in reproductive-age females, bright light therapy may activate the production of reproductive hormones, such as luteinizing hormone, follicle-stimulating hormone, and estradiol{{cite journal |vauthors=Danilenko KV, Samoilova EA |title=Stimulatory effect of morning bright light on reproductive hormones and ovulation: results of a controlled crossover trial |journal=PLOS Clinical Trials |volume=2 |issue=2 |page=e7 |year=2007 |pmid=17290302 |pmc=1851732 |doi=10.1371/journal.pctr.0020007 |doi-access=free }}

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.{{cite journal |vauthors=Terman M, Terman JS |title=Light therapy for seasonal and nonseasonal depression: efficacy, protocol, safety, and side effects |journal=CNS Spectr |volume=10 |issue=8 |pages=647–63; quiz 672 |date=August 2005 |pmid=16041296|doi=10.1017/S1092852900019611 |citeseerx=10.1.1.527.6947|s2cid=27002316 }}

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.{{cite web |title=Light Therapy Diagnostic Indications and Contraindications |url=http://www.health.am/psy/more/light_therapy1/ |publisher=American Medical Network |access-date=2009-06-09 |date=2007-12-08 |last=Gagarina |first=AK}}{{cite journal|last1=Westrin|first1=Åsa|last2=Lam|first2=Raymond W.|title=Seasonal Affective Disorder: A Clinical Update|journal=Annals of Clinical Psychiatry|date=October 2007|volume=19|issue=4|pages=239–246|doi=10.1080/10401230701653476|pmid=18058281}} 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.{{citation needed|date=November 2016}}

Side effects of light therapy for sleep phase disorders include jumpiness or jitteriness, headache, eye irritation and nausea.{{cite web |url=http://www.mayoclinic.org/tests-procedures/light-therapy/basics/risks/prc-20009617 |title=Light Therapy. Tests and Procedures. Risks. |author=Mayo Clinic Staff |date=20 March 2013 |publisher=Mayo Clinic |access-date=7 February 2014}} Some non-depressive physical complaints, such as poor vision and skin rash or irritation, may improve with light therapy.{{cite web |author=Roger DR |url=http://www.health.am/psy/more/light_therapy4/ |title=Practical aspects of light therapy |access-date=2009-06-09 |date=2007-12-04 |publisher=American Medical Network}}

File:Sun therapy at Alton Hospital Wellcome L0074520.jpg, especially of the bones and joints, laying on beds on a terrace outside Treloar Hospital in Alton, Hampshire, England, in sunlight as part of their light therapy, ca. first half of the 20th century{{Cite book|title=Soaking Up the Rays: Light Therapy and Visual Culture in Britain, C. 1890-1940|chapter=Consuming light|url=https://www.manchesteropenhive.com/view/9781526115980/9781526115980.xml|first=Tania Anne|last=Woloshyn|publisher=Manchester University Press|location=Manchester|date=2017|language=en|doi=10.7765/9781526115980|isbn=978-1-5261-1598-0}}]]

Many ancient cultures practiced various forms of heliotherapy, including people of Ancient Greece, Ancient Egypt, and Ancient Rome.F. Ellinger Medical Radiation Biology Springfield 1957 The Inca, Assyrian and early Germanic peoples 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.{{Cite book |last=Ingold |first=Niklaus |url=https://library.oapen.org/handle/20.500.12657/31817 |title=Lichtduschen Geschichte einer Gesundheitstechnik, 1890–1975 |publisher=Chronos Verlag |year=2015 |isbn=978-3-0340-1276-8 |pages=40–49 |hdl=20.500.12657/31817 |language=German}} 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.{{Cite journal|title=How Finsen's light cured lupus vulgaris |date=2014-11-12 |pmid=15888127 |doi=10.1111/j.1600-0781.2005.00159.x |volume=21 |issue=3 |journal=Photodermatol Photoimmunol Photomed |pages=118–24|last1=Moller |first1=Kirsten Iversen |last2=Kongshoj |first2=Brian |last3=Philipsen |first3=Peter Alshede |last4=Thomsen |first4=Vibeke Ostergaard |last5=Wulf |first5=Hans Christian|s2cid=23272350 |doi-access=free }} Finsen also used red light to treat smallpox lesions. He received the Nobel Prize in Physiology or Medicine in 1903.{{cite web |url=https://www.nobelprize.org/nobel_prizes/medicine/laureates/1903/ |title=The Nobel Prize in Physiology or Medicine 1903 |date=2016-11-01 |website=Nobelprize.org |publisher=Nobel Media AB |archive-url=https://web.archive.org/web/20161022202413/http://www.nobelprize.org/nobel_prizes/medicine/laureates/1903/ |archive-date=2016-10-22 |url-status=live |access-date=2016-11-01}} 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.{{cite web|url=http://www.uh.edu/engines/epi1769.htm|access-date=2014-04-05|title=Engines of our Ingenuity No. 1769: NIELS FINSEN}} In the early 20th-century light therapy was promoted by Auguste Rollier and John Harvey Kellogg.{{cite journal|author=Loignon, Austin E.|year=2022|title=Bringing Light to the World: John Harvey Kellogg and Transatlantic Light Therapy|journal=Journal of Transatlantic Studies|url=|volume=20|pages=103–128|doi=10.1057/s42738-022-00092-7|s2cid=246636998 |doi-access=free|pmc=8819196}} In 1924, Caleb Saleeby founded The Sunlight League.{{cite journal|author=Butler, A. R; Greenhalgh, I.|year=2017|title=Sanatoria revisited: sunlight and health|journal=J R Coll Physicians Edinb|url=https://www.rcpe.ac.uk/sites/default/files/jrcpe_47_3_butler.pdf|volume=47|issue=3|pages=276–80|doi=10.4997/JRCPE.2017.314|pmid=29465107 |s2cid=3403283 }}

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.{{cite journal|last1=Edwards|first1=Martin|title=Dora Colebrook and the evaluation of light therapy.|volume=104|issue=2|pages=84–6|url=http://www.jameslindlibrary.org/articles/dora-colebrook-and-the-evaluation-of-light-therapy/|journal=Journal of the Royal Society of Medicine|publisher=Royal College of Physicians of Edinburgh and Minervation Ltd|access-date=12 February 2017|pmid=21282799|year=2011|doi=10.1258/jrsm.2010.10k067|pmc=3031646}}

{{Expand section | with = Obscure light therapies with undue medical claims like Bioptron or red light therapy|date=February 2025}}

Red light therapy involves exposure to low levels of red light or near-infrared light, typically through lamps or masks.{{Cite web |last=Katzel |first=Taylor |date=February 20, 2025 |title=Does red light therapy work? Experts weigh in on TikTok skincare trend |url=https://www.cbc.ca/kidsnews/post/does-red-light-therapy-work-experts-weigh-in-on-tiktok-skincare-trend |website=CBC Kids News}} It is promoted for various skin-related benefits, including improved appearance and reduced signed of aging.{{Cite news |last=Matei |first=Adrienne |date=2024-09-25 |title=Does red light therapy work? These are the benefits and drawbacks |url=https://www.theguardian.com/wellness/2024/sep/25/what-is-red-light-therapy |access-date=2025-04-23 |work=The Guardian |language=en-GB |issn=0261-3077}}{{Cite web |last= |date=December 1, 2021 |title=Red Light Therapy |url=https://my.clevelandclinic.org/health/articles/22114-red-light-therapy |access-date=April 22, 2025 |website=Cleveland Clinic}} However, there is currently insufficient scientific evidence to support many of these claims. There has been some indication that it may reduce inflammation associated with conditions such as acne or rosacea, but evidence supporting its anti-aging effects remain limited. Most existing research has focused on in-office treatments, while at-home devices are generally less powerful and precise, which may lead to inconsistent results. It is generally considered safe, however if misused red light therapy could cause eye or skin damage.{{Cite news |last=Armitage |first=Hanae |date=February 24, 2025 |title=What’s the deal with red light therapy? |url=https://scopeblog.stanford.edu/2025/02/24/red-light-therapy-skin-hair-medical-clinics/ |work=Stanford Medicine |department=Scope}}

• Blood irradiation therapy
• Chromotherapy
• Crib A'Glow
• Free-running sleep
• Low level laser therapy
• Neuromodulation
• Neurostimulation
• Neurotechnology
• Photodynamic therapy
• Sun tanning
• UV-B lamps

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{{Commons category-inline|Phototherapy}}

• [http://digital.library.mcgill.ca/sun/ Our Friend, the Sun: Images of Light Therapeutics from the Osler Library Collection, c. 1901–1944]. Digital exhibition by the Osler Library of the History of Medicine, McGill University

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