About this calculator
Number of downlights for a room from the light level it needs, laid out on an even grid with spacing from the walls.
How it’s calculated
Lumens = target lux × area ÷ 0.7 (utilisation). Fittings = lumens ÷ lumens per fitting, arranged on a grid that follows the room’s proportions. The first light sits half a spacing from each wall.
Worked example
With these inputs:
- Room length
- 5 m
- Room width
- 4 m
- Ceiling height
- 2.4 m
- Room
- Kitchen
- Lumens per fitting
- 600
the result is:
- Fittings
- 16 lights
- Target light level
- 300 lux
- Lumens needed
- 7,500
- Spacing along length
- 1.25 m
- Spacing across width
- 1 m
Tips from the trade
- Under-cabinet and task lights are extra. Don’t count them in this figure.
- Use fire-rated downlights where the ceiling is a fire separation.
Results are estimates for planning and pricing. Check quantities against your drawings, the manufacturer’s data and the Building Regulations before ordering.