USL PCA-100 - Manual (Page 11)

PCA I
NSTRUCTION
M
ANUAL
Ultra Stereo Labs, Inc.
-10 -
Projection Stray Light
The stray light of concern includes all ambient light from sources within the
auditorium as well as lens flare from the projection lens. Measurement of the
stray light is done by projection a special test film, which has a black spot in
the center and measuring the light on the screen within the projected black
spot. The ratio of light within the black spot to light from the screen with no
film in the gate times one hundred gives the percentage of stray light. The
measurement can also be made by inserting a small, flat metal disk within the
gate in place of the test film.
Contrast Ratio
Contrast ratio is the ratio of light measurement of the lightest area of a film
scene to the measurement of the darkest area of the scene.
Diffuse Reflectance
The diffuse reflectance of the wall surfaces of an auditorium can be measured
with the aid of the reflectance standard. The reflectance standard can be held
against the wall surface and a measurement of the reflected light made. The
standard is then
removed and the light reflected from the wall is made. The
ratio of the wall-reflected light to the light from the standard is the diffuse
reflectance of the surface.