Updated 19 September 2026 · Planning guidance with linked calculators
Room Lighting Calculator checkpoint
A 4.8 m × 3.9 m living room is being compared at a 180 lux planning target with a 0.72 utilization factor.
Inputs used
| Room length | 4.8 m |
|---|---|
| Room width | 3.9 m |
| Target illuminance | 180 lux |
| Utilization factor | 0.72 |
| LED efficacy | 95 lm/W |
Calculator result
- Room area
- 18.72 m²
- Required source lumens
- 4,680 lm
- Approximate LED wattage
- 49.26 W
Decision from this checkpoint
Use the lumen requirement to compare fixture combinations, then place fittings according to tasks, beam distribution, and room features rather than a blind grid.
- Use rated lumens from the exact fixture.
- Plan reading/task lights separately from the ambient layer.
Tools referenced in this project
- Room Lighting Calculator
- Light Fixture Size Calculator
- Recessed Light Calculator
- LED Wattage Calculator
Define what the room needs to support
List the main tasks in the room before calculating a total. A living room may need flexible ambient light, while a desk, kitchen worktop, or reading chair also needs task lighting in a specific location. Accent light is a separate layer. One total lumen figure cannot tell you where all three layers should go.
Use lumens for output, not watts alone
Watts describe electrical power consumption, while lumens describe emitted visible light. Different lamp technologies can produce different lumens for the same wattage. When comparing fixtures, use the actual lumen output published for the chosen product and note whether the value is for the lamp, the complete fitting, or a particular operating mode.
Turn the target into a tentative count
Divide the chosen total output by the usable output of one fitting to get a preliminary fixture count, then round to a practical whole number. This count is only a starting point. Beam angle, ceiling height, spacing, wall reflectance, shades, diffusers, and furniture can change how evenly the light reaches the room.
Lay out fixtures around tasks and architecture
Draw the ceiling or wall positions at scale. Keep important task areas, artwork, cabinetry, and circulation visible. For recessed fittings, compare spacing with beam spread and ceiling height rather than forcing a perfect grid where it does not support the room. Dimmers and multiple circuits can make one layout more flexible, but compatibility must be checked for the selected hardware.
Separate planning from electrical approval
The calculators do not assess wiring condition, circuit capacity, bathroom zones, fire ratings, building requirements, or installation safety. Use the plan to discuss quantities and positions, then have regulated or safety-critical electrical work checked and carried out by an appropriately qualified person where required.