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Reflected Light  

post #1 of 4
Thread Starter 
This may be an elementary question but if I'm getting about 10 foot lamberts of light from my projector and I'm using a 1.8 gain screen should I get approximately 18 foot lamberts of reflected light from the screen?
post #2 of 4
Thread Starter 
post #3 of 4
Yes, your math is correct. That is exactly how a screen's "gain" works. A Unity gain screen is 1.0, i.e. it returns exactly the same FtL back that strikes it.

How does a higher gain screen "do it"? By redirectly most of the light energy back within a smaller angle of reflectance, effectively concentrating the light output for that given viewing angle range.

- Tom C
post #4 of 4
The correct formula for calculating screen luminance (in foot-lamberts) is: (projectors light output (in ansi lumens) x screen gain) / screen sq ft. . You can work this formula back and forward to derive you desired screen luminance. Once you know the projectors light output, you can play with screen size and gain to reach the desired number. Somewhere between 10-16 foot-lamberts would match the light output at the theater (they measure 16 with the gate open and no film, it ends up being about 12foot lamberts during the film presentation). You may want a higher number if you have poor control of ambient light. To get higher screen luminance:
-higher gain screen (trade offs can be numerous)
-smaller screen
-brighter projector

Don O
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