Fluke Biomedical 07-621 - Manual (Page 7)

General Information
Mode of Measurement
1
1-3
For lux measurements, the white disc is used. Place it over the light sensor. The location of the light
sensor is designated by a mark (
∧) on the instrument housing.
For candela/m
2
(Nit) measurements, place the clear aperture over the sensor.
If you have positioned the turret correctly, the measurement selected will also be indicated on the turret
tab closest to the front of the instrument.
Whichever position of the turret is chosen, the digital display will be calibrated in the corresponding unit of
measurement. Proper measuring technique is also necessary for accurate measurements, see Section
1.5.
1.5 Measuring Technique
Illuminance--Lux
This is the amount of light energy incident upon a surface. The surface is defined by the geometric plane
of the white disc on the triangular head. Light sources within the (180°) hemisphere in front of the white
disc will be sensed according to the cosine law.
For best accuracy, do not block light sources in the 180° hemisphere. The orientation of the white discs
for lux measurements is designed to minimize the effect of the operator’s presence on the reading.
Luminance--candela/m 2
Luminance is the photometric brightness of sources or of light reflected from objects. Photometers read
the overall luminance in approximately a 25° field of view, as shown below.