Up/Down Light Ratio Calculator

Calculate illuminance on the task plane and ceiling from any luminaire up/down distribution ratio. Covers direct, direct-indirect, and indirect lighting — with UGR glare estimate, ceiling luminance, and comparison of different distribution ratios for the same space.

Measurement units
Metric
Metres, lux
Imperial
Feet, foot-candles
Distribution type
Direct
100% down / 0% up
Semi-direct
80% down / 20% up
Direct-indirect
60% down / 40% up
Semi-indirect
40% down / 60% up
Indirect
10% down / 90% up
Custom ratio
set slider below
0% down (all up)50/50100% down (all down)
Room dimensions and reflectances
Luminaire specification
Task plane (down)
0
lux on floor/desk
Ceiling illuminance (up)
0
lux on ceiling
0
Down lumens
0
Up lumens
0
UGR estimate
0
Ceil luminance cd/m2
✅
UGR within limits
Room section — up/down light distribution
Distribution comparison — same total lumens
DistributionTask luxCeil luxUGREfficiency
Up/down light design guidance
Distribution
Total lumens
Task illuminance
Ceiling illuminance
UGR estimate
Ceiling luminance
Optical efficiency
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.