Radiation, Ultraviolet

ULTRAVIOLET RADIATION WAS discovered as a result of the observation that silver salts darken on exposure to sunlight. In 1801, the German physicist Johann Wilhelm Ritter first observed that invisible electromagnetic radiation was responsible for this darkening. These rays eventually became known collectively as UV, so named as this radiation is immediately beyond violet in the electromagnetic spectrum. This implies that UV is more energetic than the visible light. Conventionally, UV radiation is broken down into further subdivisions as shown in Table 1:

Table 1: Conventional subdivisions of UV radiation
1. Near400 nm–200 nmReferred to as ‘Blacklight’
UV-A400 nm-320 nmStrongly absorbed by O3
UV-B320 nm-280 nmStrongly absorbed by O3
UV-C290 nm-200 nmStrongly absorbed by O2
2. Far200 nm-31 nmStrongly absorbed by O2
3. Extreme31 nm-1 nm

In humans, UV radiation is important for ...

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