How the spotlight estimate works
Floor area multiplied by target illuminance gives a theoretical light output. Dividing by the lumens per spotlight gives a quantity, rounded up to the next whole fitting.
Formula
Theoretical light output (lm) = area (m²) × target illuminance (lux)
Spotlights = round up [theoretical light output ÷ lumens per spotlight]
Worked example
20 m² × 200 lux = 4,000 lm.
For 500 lm spotlights: 4,000 ÷ 500 = 8 spotlights. The 200 lux value is an example assumption, not a recommendation for every room.
Assumptions and limits
- The model does not account for light losses, mounting height, beam angle or surface reflections. It does not check lighting uniformity.
- The estimated quantity is not a positioning plan or an electrical circuit design.
Common questions
Should I enter watts or lumens?
Use the lumen output stated for one spotlight. Watts describe electrical power; they do not directly specify light output and cannot replace lumens in this formula.
What if the calculation gives 7.3 spotlights?
The calculator rounds up to 8 to meet the theoretical total output. You still need to check layout and fitting characteristics; rounding does not ensure sufficient light in every part of the room.