Calculate lumens, fixture count and wattage to reach a target light level.
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.
LED Lighting
Lumens = area × target lux ÷ utilisation factor
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.
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.
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.