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# Ambient Light Question....

...when using ProjectorCentrals Calculator....
I'm no good when it comes to "visualizing" lumens/fc/candlepower/etc...
Am I right in thinking that "room size" plays a key factor in lumens vs. fc? (Not from a throw standpoint, but let's say a 60w bulb in a 20x30 room vs 10x20 room)
So, given my room - 12x12 darkened except for a 60w lamp - what % or fc would that present??? Does this make any sense?
Can anyone simplify this - I've searched & read many articles on light output, and for some reason, can't put the "calculations" into practice....

I saw a simple calculation as fc = lumens/sq feet.....
But, why wouldn't it be cubic ft??? I mean, light is not 2 dimensional??

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Quote:
Originally Posted by rumonkey2

...when using ProjectorCentrals Calculator....
I'm no good when it comes to "visualizing" lumens/fc/candlepower/etc...
Am I right in thinking that "room size" plays a key factor in lumens vs. fc? (Not from a throw standpoint, but let's say a 60w bulb in a 20x30 room vs 10x20 room)
So, given my room - 12x12 darkened except for a 60w lamp - what % or fc would that present??? Does this make any sense?
Can anyone simplify this - I've searched & read many articles on light output, and for some reason, can't put the "calculations" into practice....

I saw a simple calculation as fc = lumens/sq feet.....
But, why wouldn't it be cubic ft??? I mean, light is not 2 dimensional??

Its a function of distance and the inverse square law. Its not cubic feet because you care about light on a surface (like say your screen).

What ambient light is on your screen in a 12x12 room depends on how close that 60w light is to your screen and which way its pointing (unless a bare bulb shining in all directions). Then you have to consider what color your walls are for reflections.

Figure that your 60w bulb is 800-900L (call it 65 candela if I remember the conversion right) and figure out the distance and plug into formula.

fc = cd / d^2 so for 12 feet it is 65 / 144 = .45 fc

Hmmm...I should google that to be sure since I did that from memory. Probably did something wrong.

Nigel
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