4
UNITS OF MEASUREMENT
Ultra-Violet (UV)
Traditionally UV has been measured in museums as the proportion of ultraviolet
present. This result is useful for checking a particular lamp or window because the
proportion of UV does not change with the distance from the light source. Using a
simple rule the amount of UV on an object can be limited. It is usual to arrange that
the proportion of UV should not exceed 75µW/lumen in museums and galleries,
though some organisations try to keep UV levels below 25µW/lumen
The damage is done by the total amount of UV falling on the object so it is useful to
be able to measure this directly, especially if non standard amounts of illumination are
required. The amount of UV should be as little as possible but in general should not
exceed 20mW/M
2
, again some organisations keep the level below 6mW/M
2
.
Both the above units are displayed when the UV button is pressed, one in large
characters, the other smaller at the bottom of the screen. Which is displayed where can
be swapped by pressing Set\Units\µW/Lumn-mW/M².
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