Ultraviolet light can be divided into different subtypes based on wavelength. These correlate with the imparted energy of the light and its consequences. They may be encountered in natural sunlight or light from other sources (such as tanning beds).
Spectrum of ultraviolet light: 0.1 to 399 nm
Spectrum of visible light: 400 to 780 nm
Range of ultraviolet light important to the skin: 200 to 399 nm
Type
Wavelengths
Effect
UVC
200 to 289 nm
UVB
290 to 319 nm
most carcinogenic, persistent erythema
UVA2
320 to 339 nm
photoaging, immediate erythema
UVA1
340 to 399 nm
induction of cytokines
The impact of a given wavelength depends on:
(1) its intensity
(2) interference by clouds or atmosphere
(3) sunscreen or other skin coverings
(4) skin color
(5) duration of exposure
When selecting a sunscreen it is important to know how well it will protect against each type of ultraviolet light.
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