A Wood’s lamp is a hand-held device that emits long-wave ultraviolet radiation through a nickel or cobalt glass filter. The filter is opaque to all light except a band between 320 and 400 nm. Fluorescence occurs when shorter wavelengths are absorbed and radiation of longer wavelengths (visible light) is emitted.
The Wood’s lamp was invented in 1903 by Baltimore physicist Robert Wood. In human medicine it is used to detect dermatophyte infections, bacterial infections, porphyria, and pigmentary diseases. In veterinary medicine, Wood’s lamps are most commonly used to help identify dermatophytosis caused by Microsporum canis. (Trichophyton species and M gypseum infections do not produce metabolites that cause fluorescence.) They are also useful when examining hairs under the microscope for evidence of ectothrix infections and occasionally as an aid in monitoring therapy.