Digital Projection HIGHlite 5000GV, User Manual

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The projector's arc lamp emits a luminous flux measured in lumens. This flux is
directed at the screen and illuminates it, the illuminance (E) can be measured in Lux
(lumens/m2) or Foot Candles (lumens/ft 2 ). The illuminance of the screen is
calculated by dividing the incident flux by the illuminated screen area.
The brightness of the screen, known as the screen luminance (B) is determined by
the amount of light reflected from it (or transmitted through it if using a rear
projection screen). If the screen is diffuse, the incident light is reflected into a
hemisphere. If the screen has a reflectivity (R), the screen luminance in candela/m 2
is given by (R x E) /
π
, where E is measured in Lux. If E is measured in Foot-
Candles, the screen luminance is in Foot-Lamberts, and is given by R x E.
Examples:
1) A 6' x 4' 6" diffuse screen, with a reflectivity of 0.8 is illuminated by a projector
emitting 3000 lumens.
The screen illuminance (E) = F / A = 3000 / 27 = 111 Foot-Candles
The screen luminance (B) = R x E = 0.8 x 111 = 89 Foot Lamberts
2) A 4m x 3m screen with a reflectivity of 0.85 is illuminated by a projector
emitting 3500 lumens.
The screen illuminance (E) = F / A = 3500 / 12 = 292 Lux
The screen luminance (B) = (R x E) /
π
= (0.85 x 292) /
π
= 79 Candela/m 2
D—1
Advanced User Information
Screen Illuminance
ADVANCED
LBV00063; Revision A - 01/02/2000