Calculate how many fixtures or bulbs are needed to hit a target light level (foot-candles) in a room.
Uniformity
Usage Tip
Spread fixtures evenly and add dimming; it is easier to dim ample light than to live with too little.
fixtures = round up( total lumens ÷ lumens per fixture )
The result rounds up to whole fixtures.
How many lights does a room need?
Good lighting is two questions, not one: how much light, and where to put it. The amount comes from the lumen method — multiply the target light level (in footcandles) by the room area, allow for the fact that not all light reaches the floor, and divide by the lumens each fixture puts out. The placement comes from spacing the fixtures evenly so the room is lit edge to edge instead of in bright pools with dim corners. This designer does both: it works out the fixture count and then lays them on a grid sized to the room, with a coverage preview so you can see the result.
Recommended light levels
Target footcandles by room (one footcandle is one lumen per square foot at the surface):
| Room | Footcandles |
|---|---|
| Living room / bedroom | 10 to 20 |
| Kitchen | 30 to 50 |
| Office | 30 to 50 |
| Bathroom | 30 to 50 |
| Garage | 50 |
| Workshop | 50 to 100 |
| Retail | 50 to 75 |
| Warehouse | 20 to 30 |
Recessed light spacing rule
The quick rule electricians use: space recessed downlights apart by about the ceiling height divided by two. An 8 ft ceiling gives roughly 4 ft between lights; a 10 ft ceiling about 5 ft. Keep the first row about half that distance from the walls. The rule keeps the pools of light overlapping so the floor reads as evenly lit. Higher targets or task areas pull the spacing tighter.
Beam angle
The beam angle sets how wide each fixture throws light, which changes how far apart they can sit:
| Beam | Use |
|---|---|
| 15° | Accent — spotlighting art or features |
| 24° | Narrow — high ceilings, focused pools |
| 36° | General — most rooms |
| 60° | Wide — low ceilings, wall washing |
Uniformity: more lights is not always better
The instinct is to add fixtures until the room is bright, but that is the wrong target. What matters is uniformity — even light with no harsh bright spots or dim corners. Too few fixtures gives gloomy corners; cramming in too many gives flat, shadowless glare that, as more than one homeowner has discovered, makes the living room feel like an operating theatre. Even spacing at the right level beats raw quantity every time. The coverage preview here shows where the light overlaps and where it falls off.
Frequently asked questions
How many recessed lights for a 15×20 room?
About eight at 800 to 1,000 lumens each for a living space, laid out 2 rows by 4, roughly 5 ft apart.
How far apart should recessed lights be?
Roughly the ceiling height divided by two — about 4 ft on an 8 ft ceiling, 5 ft on a 10 ft ceiling.
How do I calculate lights for a room?
Multiply target footcandles by area, divide by lumens per fixture, allowing for light loss. Then space them evenly on a grid.
What beam angle for 9 ft ceilings?
About 36 degrees for general lighting; go narrower for higher ceilings and wider for lower ones.
How far from the wall should recessed lights be?
About half the fixture-to-fixture spacing, often 2 to 3 ft, to light the walls without scalloping.
Is it better to have more smaller lights or fewer brighter ones?
More smaller fixtures, evenly spaced, give better uniformity than a few bright ones that leave dim gaps.
Beam Angle Calculator · LED Driver Calculator
Coming soon: Recessed Lighting, Lux and Footcandle calculators
Estimates use the lumen method with a typical utilization and light-loss allowance, for planning and education. Actual results depend on fixture optics, reflectance of walls and ceiling, mounting height and furnishings. For critical or commercial spaces, confirm with a photometric layout. Have wiring done by a qualified person and follow local code.