# Usable lumen question, bunch of assuming going on again.



## 10492 (Jan 4, 2010)

Assume you have a bulb, don't matter what type so much but follow me here.

Assume the bulb is a horizontal mount, and the bulb is recessed back into the fixtures reflector, so that none of the bulb is forward more,then the reflectors outer edges.

Let's also assume that the bulb puts out 10,000 lumens.

As I keep assuming....what if the reflector is rated at 65% reflectivity?

Would it be a safe assumption to think the usable lumens from this light source is only 6500 lumens at best?


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## jw0445 (Oct 9, 2009)

Theoretically i believe it would be more. You only have reflectiveness from 3 sides and to top of the bulb. The outward facing side would not have light reflecting off the reflector. In other words you would have 65% from the bottom, top, back, and the one side but not the front. You can actually figure it out if you assign lumens and multiply by the 65% factor. Let's say all sides are equal including the top. There are a total of 5 sides, so each side would then be 2000 lumens. So 2000 X 4 X 65% is 5200 lumens. Add the front of the bulb at 2000 and your total is 7200 lumens output.


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## The Lightman (Jan 9, 2010)

*Light Loss Factors (more on **Light Loss**)*
Light Loss Factor (LLF) = Ballast Factor x Fixture Ambient Temperature Factor x Supply Voltage Variation Factor x Lamp Position Factor x Optical Factor x Fixture Surface Depreciation Factor x Lamp Burnouts Factor x Lamp Lumen Depreciation Factor x Fixture Dirt Depreciation Factor x Room Surface Dirt Depreciation Factor


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## 10492 (Jan 4, 2010)

The Lightman said:


> *Light Loss Factors (more on **Light Loss**)*
> Light Loss Factor (LLF) = Ballast Factor x Fixture Ambient Temperature Factor x Supply Voltage Variation Factor x Lamp Position Factor x Optical Factor x Fixture Surface Depreciation Factor x Lamp Burnouts Factor x Lamp Lumen Depreciation Factor x Fixture Dirt Depreciation Factor x Room Surface Dirt Depreciation Factor


 

:laughing::laughing::laughing::laughing:

Bravo.

I see I missed the fixture surface depreciation factor in my assumptions....:laughing:


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