Jadak Photo Research SpectraScan PR-7 Series, Руководство пользователя

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Chapter 9
– How to Make an Illuminance / Irradiance
Measurement
93
Chapter - 9 H
OW TO
M
AKE AN
I
LLUMINANCE
/
I
RRADIANCE
M
EASUREMENT
I
LLUMINANCE
/ I
RRADIANCE
Illuminance is defined as the density of luminous flux incident on a surface, or light falling on a surface per area,
and is calculated from
Irradiance (watts/meter²) . Three factors help determine illuminance: the luminous flux of
the source, the angle of incidence of the light falling on the plane, and the distance from the source to the
measured plane. Illuminance is given by
lux (lumens per meter²) and footcandles (lumens per foot²). The
relationship between footcandles and lux is: 1 footcandle = 10.76 lux. In the following example, the light falling
on the measured plane is the illuminance.
FIGURE 79 - ILLUSTRATION OF ILLUMINANCE
Illuminance measurements are made one of three ways with the PR-7XX. The first method involves the use of
the CR-730 cosine receptor. The second method utilizes the use of a reflectance standard such as the RS-3 or
SRS-3, and for the third method the ICC-730 integrating sphere accessory is employed.
The CR-730 is a diffuser that serves as the surface upon which the incident light falls. During calibration these
accessories are photometrically calibrated using a standard lamp whose candela rating has been certified to
NIST standards. By knowing the candelas of the lamp, the illuminance can be calculated by:
Source
Measured
plane
Distance
Lumen
s