Room Lighting Lumens and Fixture Count Calculator
Estimate whole fixture count and average maintained illuminance from an entered light-level target and utilization assumptions.
YOUR CALCULATION
Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Multiply target illuminance by area for useful lumens. Reduce each fixture’s rated lumens by the two entered fractions, round the required fixture count upward and calculate the resulting average and total input power.
Count=ceil(target lux×area m²/(fixture lumens×utilization×maintenance)); average lux=useful lumens/area
Worked example
24 m² at an entered 200 lux target needs 4800 useful lumens. A 1500 lm fixture at 60% utilization and 80% maintenance supplies 720 useful lumens; seven fixtures give 210 lux average and consume 140 W at 20 W each.
Assumptions and input details
An average lumen-balance estimate, not a measured lighting plan. Target and both fractions are user choices; no activity-specific standard is prescribed. Fixture distribution, mounting height, glare, daylight, reflections, color quality and local uniformity are not calculated separately. Utilization should reflect the intended target plane. Rated fixture lumens and input watts are different quantities. One footcandle is exactly one lumen per square international foot; displayed results are rounded.
References: US DOE: lighting quantities and specification terms
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
SI prefixes are explicit: for example, milli means one thousandth, micro one millionth and kilo one thousand. Changing a unit changes the interpretation of the entered number.
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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