Monday, November 14, 2011

Determining Light Loss Factor

From the Illuminating Engineering Society North America Lighting Handbook:

The light loss factor (LLF) is a fraction that represents the amount of light that will be lost due to things such as dirt on lamps, reduction of light output of a lamp over time, and similar factors. The following items are the individual components of the light loss factor.The total LLF is calculated by multiplying all the individual factors together. No factor should be ignored (set equal to 1) until investigations justify doing so. Lighting calculations should not be attempted until all light-loss factors are considered.

•Luminaire Ambient Temperature Factor
•Heat-extraction thermal factor
•Voltage-to-luminaire factor
•Ballast Factor
•Ballast-lamp photometric factor
•Equipment operating factor (H.I.D. only)
•Lamp-position (tilt) factor (H.I.D. only)
•Luminaire surface depreciation factor


•Lamp Lumen Depreciation
•Luminaire Dirt Depreciation
•Room Surface Dirt Depreciation
•Lamps Burnout Factor

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