How many lumens does a room need?
Lighting designers start from the illuminance a room needs, the light falling on surfaces, measured in foot-candles (lumens per square foot) or lux (lumens per square meter). Multiply it by the floor area to get the total lumens the fixtures must provide, then divide by the output of your bulbs.
The formulas
- Lumens = area × target illuminance × room factor
- Bulbs = lumens ÷ lumens per bulb, rounded up
- LED watts ≈ lumens ÷ 100 (modern LEDs give about 100 lm per watt)
- Incandescent equivalent ≈ lumens ÷ 13.3
Dark walls, dark floors or ceilings over 9 feet absorb or spread more light; the room factor adds 25% in that case.
Worked example
A 200 sq ft living room with light walls, at about 15 foot-candles:
- 200 sq ft is 18.6 m², and 15 fc is about 150 lux.
- Lumens: 18.6 × 150 = 2,787 lumens.
- With 800-lumen bulbs (60 W equivalent): 2,787 ÷ 800 = 3.5, so 4 bulbs.
- That is about 28 W of LED, instead of 210 W with old incandescent bulbs.
Recommended light levels
| Room | Foot-candles | Lux |
|---|---|---|
| Hallway, garage, storage | about 10 | 100 |
| Living room, bedroom | about 15 | 150 |
| Kitchen, bathroom | about 30 | 300 |
| Home office, workshop | about 50 | 500 |
| Detailed crafts, sewing | about 75 | 750 |
These are general lighting levels. Kitchens, desks and vanities benefit from extra task lighting where you work, rather than from brighter ceiling lights everywhere.
Lumens, not watts
Since LEDs replaced incandescent bulbs, watts no longer tell you how bright a bulb is. Packaging lists lumens, with the old wattage as an equivalent: 450 lumens for 40 W, 800 for 60 W, 1,100 for 75 W and 1,600 for 100 W.
Color temperature and dimming
Brightness is only part of the picture. Warm white (2,700 to 3,000 K) suits living rooms and bedrooms; neutral white (3,500 to 4,000 K) suits kitchens and offices. Dimmers let you install enough lumens for tasks and turn them down in the evening.