LED Lighting Calculator
Calculate lumens, fixture count and wattage to reach a target light level.
About LED Lighting Calculator
Not all emitted light reaches the working plane, so the utilisation factor raises the lumens required. Power then follows from efficacy, which is what separates a good LED fixture from a poor one at equal output. Specifying by wattage is a habit from incandescent lighting and no longer means anything; lumens and efficacy are the figures that determine both light level and running cost.
Formula
LED Lighting
Lumens = area × target lux ÷ utilisation factor
- lux
- Lumens per square metre falling on the working plane
- utilisation factor
- Share of emitted light reaching the working plane after losses
Worked example
With the default values below, LED Lighting Calculator returns Fixtures Required of 6. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Room areaminimum 0.1 m2
- 20 m2
- Target illuminanceminimum 10 lux
- 300 lux
- Lumens per fixtureminimum 10 lm
- 1,600 lm
- Fixture efficacyminimum 10 lm/W
- 110 lm/W
- Light utilisation factoraccepts 10–100 %
- 70 %
Results
- Fixtures Required
- 6
- Total Lumens Required
- 8,571 lm
- Total Power
- 87.27 W
- Power Density
- 4.364 W/m2
- Illuminance Achieved
- 336.0 lux
Step by step
- 1Values used
- 2LED Lighting
- 3Fixtures Required= 6
- 4Total Lumens Required= 8,571 lm
- 5Total Power= 87.27 W
- 6Power Density= 4.364 W/m2
- 7Illuminance Achieved= 336.0 lux
Assumptions and limits
- The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
- Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is LED Lighting calculated?
Lumens = area × target lux ÷ utilisation factor Not all emitted light reaches the working plane, so the utilisation factor raises the lumens required. Power then follows from efficacy, which is what separates a good LED fixture from a poor one at equal output.
Why does LED Lighting matter?
Specifying by wattage is a habit from incandescent lighting and no longer means anything; lumens and efficacy are the figures that determine both light level and running cost.
What values do I need to enter?
This calculator takes 5 inputs: Room area, Target illuminance, Lumens per fixture, Fixture efficacy, Light utilisation factor. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.