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Discussion Starter · #1 ·
Given the area and gain of a screen, what is the formula for calculating total lumens once you have a ft-Lambert reading? I found the following but am unclear with where to apply the values?


B = (k*E)(1/pi)

Bfl = k*E


where: B = luminance, candles/foot^2

Bfl = luminance, foot-Lamberts

k = reflectivity 0<k<1

E = illuminance in foot-candles (lumens/ foot^2)
 

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ft/lamberts = (pj lumens * screen gain)/screen area in square feet. If you know 3 of the variables, you can solve for the 4th - for example

pj lumens = (ft/lamberts * screen area in square feet)/screen gain (i think that's right... it's been 8 yeas since algebra)


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Without wanting to divert this thread...


What would people estimate the screen gain (or lack of it) from blackout material vinyl side ?? It looks bright white and kind of reflective and I have been happy with it enough that for my el cheapo and temporary setting it does fine...


Just wanted to make some calculations...


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