Lighting
Lighting dimensions and levels
Lighting is the only element of a room that is invisible until it is wrong, and then it is the only thing you can see.
Short answer
Work from illuminance, not bulb count: a living room wants roughly 10 to 20 foot-candles (110 to 215 lux), a kitchen 30 to 40 fc with 70 to 80 fc at the work surface. Multiply by the floor area to get a starting lumen target, then split it across ambient, task and accent layers.
The numbers, at a glance
- Living room target
- 10 to 20 fc (110 to 215 lux)
- Kitchen general / task
- 30 to 40 fc / 70 to 80 fc
- Downlight spacing, 8 ft ceiling
- About 5 to 6 ft (1.5 to 1.8 m)
- Downlight offset from a wall
- 24 to 36 in (61 to 91 cm)
- Domestic colour temperature
- 2700 K, 3000 K in wet rooms
- Colour rendering
- CRI 90+, R9 above 50
Domestic lighting advice usually arrives as a bulb count, which is the least useful form the information can take. A bulb count depends on the fixture, the shade, the ceiling height, the wall colour and what you intend to do in the room. Illuminance does not: it is the amount of light landing on the surface you care about, and it is what the Illuminating Engineering Society publishes recommendations for.
Start there, convert to lumens, then decide how many fixtures deliver it.
The rough arithmetic and its honest caveat#
The consumer formula is:
Lumens = floor area in square feet x target foot-candles
A 12 x 14 ft (3.7 x 4.3 m) living room is 168 sq ft. At 15 fc that is about 2,500 lm.
The caveat, which almost no consumer page mentions: that formula assumes every lumen a fixture makes reaches the surface. In reality a fraction is absorbed by the shade, the walls and the ceiling. Lighting engineers apply a coefficient of utilisation and a light loss factor, and in a normal room with mid-tone walls the two together can mean you need 1.3 to 2 times the naive figure of installed lumens. Treat the simple number as a floor, put it on dimmers, and build the room out of several sources rather than one.
| Room | Target | 168 sq ft needs | Notes |
|---|---|---|---|
| Living room | 10 to 20 fc | 1,700 to 3,400 lm | Weight it towards lamps, not the ceiling |
| Kitchen general | 30 to 40 fc | 5,000 to 6,700 lm | Plus 70 to 80 fc at the worktop |
| Dining room | 20 to 30 fc | 3,400 to 5,000 lm | Dimmable, warm, low glare |
| Bedroom | 10 to 20 fc | 1,700 to 3,400 lm | Bedside light on its own switch |
| Bathroom vanity | 70 to 80 fc | 1,600 lm at the face | Cross-lit, CRI 90+ |
| Home office | 40 to 50 fc | 6,700 to 8,400 lm | Task light does most of the work |
| Hall and stairs | 5 to 10 fc | 800 to 1,700 lm | Even, no dark treads |
In this section#
- Colour temperature and CRI at home2700K is the domestic default, 3000K for kitchens and bathrooms. Specify CRI 90+ with R9 above 50, and match Kelvin within a 3-step MacAdam ellipse.
- How many lumens a room needsLumens = floor area x foot-candles, then multiply by 1.3 to 2. A 12 x 14 ft living room needs 3,300 to 5,000 installed lumens, a kitchen 7,500 to 10,000.
- How to plan layered lightingAmbient 50 to 60% of lumens, task 25 to 30%, accent 10 to 15%, decorative 5%. Light three height bands, one switched circuit per layer.
- Recessed lighting spacing and placementSpacing = height above the work plane x the spacing criterion. On an 8 ft ceiling that is 5 to 6 ft between downlights, and 24 to 36 in off the wall.
- Sizing and hanging pendants and chandeliersFixture diameter = table width minus 12 in. Hang 30 to 36 in above a table on an 8 ft ceiling, plus 3 in per extra foot. 84 in clear over any walkway.