L203 Photometer
Irradian Limited
13
(continued):
MEASURING LUMINANCE WITH THE L203 & THE FOV-CIE-112/101
Measuring luminance requires either the field of view probe and detector
/ filter combination to be pointed at a radiating surface or extended
source, or the CRT contact probe and detector / filter combination to be
in contact with a radiating surface or extended source. The field of view
probe will measure the average luminance within the area subtended by
its 6° field of view whereas the contact probe will average over the
contact area. For small area measurement with the field of view it will be
necessary to bring the probe close to the surface. Care must be taken
not to shadow the surface with the probe or yourself if the surface
luminance is produced by predominantly reflected light.
Luminance is independent of the measuring distance for a uniform
Lambertian infinite sized source, because the sampled area increase
cancels the inverse square law losses.
For luminance measurements of small areas it may be preferable to use
the Irradian Spot measuring Unit model SMU 203 as the reflex viewing
optics allows the user to determine the precise measurement area.
1) Set up the photometer as outlined in section 3 with either luminance
probe fitted and the units set to either cd.m
-2
or fL.
2) Point the detector at the reflecting surface or self luminous source or
press the contact probe squarely and firmly onto the surface and
record the value on the display.
3) The display can be read directly for all light levels from 0.0000* to 199
990 cd.m
-2
or fL (*
with CIE-FOV-112 only
). Note for luminance values
of 20 000 to 199 990 cd.m
-2
or fL, the x10 LED will illuminate and the
displayed value must be multiplied by 10.
CONVERSION FACTORS
1 cd.m
-2
=
0.292 footLamberts