A Woo's lamp is a diagnostic tool used in dermatology by which ultraviolet light is shone (at a wavelength of approximately 365 nanometers) onto the skin of the patient; a technician then observes any subsequent fluorescence. For example, porphyrins — associated with some skin diseases — will fluoresce pink. Though the technique for producing a source of ultraviolet light was devised by Robert Williams Wood in 1903 using "Wood's glass", it wasn't until 1925 that the technique was used in dermatology by Margarot and Deveze for the detection of fungal infection of hair.