Optimum wavelength characteristics for phototherapy utilizing deep ultraviolet light-emitting diodes

In the early 1980s, 313-nm wavelength was reported to have potential efficacy for treating psoriasis [ [1] Parrish J.A. Jaenicke K.F. Action spectrum for phototherapy of psoriasis. J. Invest. Dermatol. 1981; 76: 359-362 Abstract Full Text PDF PubMed Scopus (430) Google Scholar , [2] Berne B. Fischer T. Alsins J. Ultraviolet-action spectrum and evaluation of ultraviolet lamps for psoriasis healing. Int. J. Dermatol. 1984; 23: 633-637 Crossref PubMed Scopus (55) Google Scholar ]. A fluorescent lamp emitting selective ultraviolet B (UVB) light ranging from 311 to 313 nm was developed for narrowband UVB therapy and widely used to treat various skin diseases, such as psoriasis, vitiligo, atopic dermatitis, and mycosis fungoides [ 3 van Weelden H. De La Faille H.B. Young E. van der Leun J.C. A new development in UVB phototherapy of psoriasis. Br. J. Dermatol. 1988; 119: 11-19 Crossref PubMed Scopus (277) Google Scholar , 4 Herzinger T. Berneburg M. Ghoreschi K. Gollnick H. Hölzle E. Hönigsmann H. Lehmann P. Peters T. Röcken M. Scharffetter-Kochanek K. Schwarz T. Simon J. Tanew A. Weichenthal M. S1-Guidelines on UV phototherapy and photochemotherapy. JDDG – J. Ger. Soc. Dermatol. 2016; 14: 853-876 PubMed Google Scholar , 5 Honig B. Morison W.L. Karp D. Photochemotherapy beyond psoriasis. J. Am. Acad. Dermatol. 1994; 31: 775-790 Abstract Full Text PDF PubMed Scopus (54) Google Scholar ]. Narrowband UVB lamps contain mercury, however, and thus have a large environmental burden. In the early 2000s, targeted phototherapy devices using a xenon-chloride excimer laser or lamp emitting 308 nm as a mercury-free light source were developed to treat localized lesions without unnecessary exposure of the unaffected skin to UV light [ [6] Aubin F. Vigan M. Puzenat E. Blanc D. Drobacheff C. Deprez P. Humbert P. Laurent R. Evaluation of a novel 308-nm monochromatic excimer light delivery system in dermatology: a pilot study in different chronic localized dermatoses. Br. J. Dermatol. 2005; 152: 99-103 Crossref PubMed Scopus (88) Google Scholar ], but these devices are costly and therefore not suitable for treating large areas. The luminous efficiency of deep UV light-emitting diodes (DUV-LEDs) has remarkably improved [ [7] Hirayama H. Fujikawa S. Kamata N. Recent progress in AlGaN-based deep-UV LEDs. Electron. Commun. Jpn. 2015; 98: 1-8 Crossref Scopus (114) Google Scholar ]. DUV-LEDs are also a mercury-free light source, and can be used for large area devices by configuring multiple DUV-LEDs. Various device types with reduced size and weight can be designed using DUV-LEDs. Furthermore, DUV-LEDs with an optimum peak light wavelength can be used for phototherapy because DUV-LEDs are made of AlGaN, and the emission wavelength can be changed by altering the composition ratio of Al and Ga [ [8] Kneissl M. A brief review of III-nitride UV emitter technologies and their applications. in: Kneissl M. Rass J. III-Nitride Ultrav Emit. Springer International Publishing, Switzerland, Heidelberg2016: 1-26 Crossref Scopus (45) Google Scholar ]. The full width at half maximum (FWHM; the wavelength width at 50% of the maximum intensity) of DUV-LEDs differs from that of traditional light sources such as the narrowband UVB and excimer lamps. The FWHM of a narrowband UVB lamp or excimer light source is approximately 5 nm [ [9] Kobayashi K. Yasuda Y. Shintani Y. Sumitomo T. Saga T. Kimura M. Yamamoto A. Mori T. Maeda A. Yamaguchi Y. Morita A. The development of a filter to enhance the efficacy and safety of excimer light (308 nm) therapy. Photodermatol. Photoimmunol. Photomed. 2009; 25: 30-36 Crossref PubMed Scopus (15) Google Scholar ], while the FWHM of the DUV-LEDs available for commercial use is approximately 10 to 20 nm. Even if it has the same peak wavelength, as FWHM increases, light on the short wavelength side relatively increases. Because the absorption coefficient of DNA greatly changes at wavelengths around 300 nm [ [10] Sutherland J.C. Griffin K.P. Absorption spectrum of DNA for wavelengths greater than 300 nm. Radiat. Res. 1981; 86: 399 Crossref PubMed Scopus (160) Google Scholar ], slight differences in the spectral distribution may largely affect the clinical results. Therefore, we studied the optimum wavelength characteristics when utilizing DUV-LEDs for phototherapy.