International Academy of Cosmetic Dermatology
The Wood’s light, sometimes called a black light, was invented in 1903 by Robert W. Wood, a Baltimore physicist. It was first used in dermatology by Margarot and Deveze to detect fungal infection in hair.
To achieve the emission of long-wave UV radiation (black light), a high pressure mercury arc is covered by a compound filter made of barium silicate with 9% nickel oxide. This compound filter is referred to as a “Wood’s filter.” The Wood’s filter only permits the emission of radiation between 320 and 400 nm with a peak at 365 nm. Initially, the skin absorbs the long-wave UV radiation (black light) and then emits radiation >400 nm which is visible.
The Wood’s light is useful in a variety of skin conditions:
- Vitiligo. Depigmented, as opposed to hypopigmented skin, glows white
- Tinea versicolor. Malassezia furfur, a yeast causing tinea versicolor, emits a yellowish-white or copper-orange fluorescence.
- Pseudomonas infection. This bacteria can create a green fluorescence.
- Erythrasma. Corynebacterium minutissimum, the bacteria that causes, erythrasma, an infection involving interdigital web spaces and intertriginous areas, gives acoral red fluorescence
- Porphyria. When shined on the urine of patients with certain types of porphyria, the Wood’s light creates reddish fluorescnence.
Noah Scheinfeld, MD, JD
New York, NY, USA