From the Guidelines
A Woods lamp emits ultraviolet light with a wavelength of approximately 365 nanometers (nm). This specific wavelength falls within the long-wave ultraviolet A (UVA) spectrum, which is why Woods lamps appear as a purple-blue light when activated 1. The 365 nm wavelength is particularly useful in medical settings because it causes certain substances and microorganisms to fluoresce, making them visible to the naked eye. For example, fungal infections like tinea capitis will glow a bright green-yellow color, while bacterial infections such as erythrasma produce a coral-red fluorescence.
Key Points
- The Woods lamp is a hand-held ultraviolet (UV) irradiation device that emits UVA 1.
- The lamp works because the UV light excites electrons in certain molecules, causing them to emit visible light when they return to their ground state.
- This property makes Woods lamps valuable diagnostic tools in dermatology, allowing clinicians to identify skin conditions that might otherwise be difficult to diagnose through visual inspection alone.
Clinical Application
The Woods lamp is used to identify areas of depigmentation that may not be visible to the naked eye, especially in pale skin 1. It is also useful in documenting pigmentary disorders, such as vitiligo, and can be used to assess the effectiveness of treatment 1.
Wavelength Spectrum
The UVA spectrum, which includes the 365 nm wavelength emitted by Woods lamps, is defined as 315-400 nm 1. This spectrum is further divided into long-wave UVA (340-400 nm) and short-wave UVA (315-340 nm). The 365 nm wavelength falls within the long-wave UVA spectrum.
From the Research
Woods Lamp Wave
- The woods lamp wave is in the range of 340-450 nm, with a maximum wavelength of 365 nm 2
- This range of ultraviolet radiation is used to diagnose dermatoses with characteristic fluorescence, such as tinea capitis, erythrasma, and tinea versicolor 2
- The woods lamp is also used to detect medications that are taken systemically or applied to the skin, and to monitor and quantify skin protection at the workplace 2
- The woods lamp projects ultraviolet light onto the skin, which reflects a visible light that can be used to diagnose and monitor multiple dermatological ailments 3