Lighting
Lux Lumens Calculator
Lux Lumens helps you find average illuminance from lumens reaching surface and surface area. The page keeps the arithmetic visible so you can check the result against the original measurements.
Enter values for Average illuminance
Use measurements from one operating condition.
Formula used on this page
For this worksheet, the governing relationship is lux = lumens ÷ area. Its variables correspond to Lumens reaching surface and Surface area.
The initial scenario returns 200.00 lx. Re-enter field data before using the answer in a design or comparison.
Calculate average illuminance from lumens reaching surface and surface area. Continue with Foot-Candles Lux Calculator to evaluate illuminance.
A second scenario
Change Lumens reaching surface from 4000 lm to 4800 lm with every other entry unchanged. The result changes from 200.00 lx to 240.00 lx.
Use a separate scenario when multiple conditions change together.
Measurements and entries
Use photometric data for the actual fixture, optic, mounting height, and task plane. A source note beside each entry makes the result reproducible.
At least one field has a positive lower bound because it appears in a denominator. A prefix error can move the result by several orders of magnitude. A separate tray fill result is available from Cable Tray Fill Calculator.
- Lumens reaching surface
- Default example: 4000 lm. Enter lumens reaching surface in lm.
- Surface area
- Default example: 20 m². Enter surface area in m².
Input quality checks
Unit-prefix mistakes often dominate the arithmetic error.
Check the input source before adding a safety or correction factor.
How to use the result
The primary answer, Average illuminance, describes only the entered scenario. Compare it with initial, maintained, and worst-case lighting conditions.
Save the raw entries before testing another scenario. Candela Lumens Calculator may be useful for the next related quantity.
Where this estimate can fail
Uniform distribution is assumed.
The equation does not include daylight variation, control behavior, depreciation, and spatial uniformity. Document which effects were checked elsewhere in the analysis.
Use photometric data for the actual fixture, optic, mounting height, and task plane.
Review the case step by step
Check the source of lumens reaching surface before calculating. A credible result requires every field to describe the same physical condition and unit basis.
After calculating average illuminance, compare its magnitude with initial, maintained, and worst-case lighting conditions. An independent order-of-magnitude check can reveal a misplaced decimal or unit prefix.
Document any effect handled outside this page, especially driver efficiency, optical loss, surface reflectance, and beam-edge definition. That note prevents a later reader from assuming the simple equation covered it.