How many downlights for a 4 m × 4 m room?
9 downlights 3 × 3, 133 cm (52 in) apart
A 4 × 4 m room with a 2.4 m (7 ft 10 in) ceiling takes 9 downlights in a 3 × 3 grid, 133 cm (52 in) apart and 67 cm (26 in) from the walls. As a living room's ceiling light, each one then needs to give only about 111–217 lumens, so choose dimmable ones.
The spacing comes from the ceiling height, not the floor area: a downlight throws a cone, and the cones must overlap by the time they reach the height you work at. Set them closer and the ceiling looks like a runway. Set them wider and the floor shows pools of light with dull patches between.
Keep the outer row in from the walls by half the spacing. Closer than that, each light draws a bright scallop on the wall and shows every flaw in the plaster.
Worked out for A room 4 × 4 m (13 ft 1 in × 13 ft 1 in) with a flat 2.4 m (7 ft 10 in) ceiling, lit from the ceiling by downlights alone. Change the numbers
The working
- Downlights: 2.4 m × 0.5 = 1.2 m apart, so 3 × 3, 1.33 m × 1.33 m apart and 0.67 m × 0.67 m from the walls.
These are targets for every light on at once. You will rarely run them all together, so fit dimmers.
The rule, and its source
Downlight spacing
A rule installers use: space downlights about half the ceiling height apart (1.2 m under a 2.4 m ceiling), and half that again from the walls (about 60 cm).
A rule designers use Source: Philips Hue, How far should recessed lights be from the wall? (checked 31 October 2026).
Other room sizes
The same ceiling height, so the same spacing rule. The grid grows a row or a column at a time.
| Room | Downlights | Apart |
|---|---|---|
| 3 × 3 m | 93 × 3 | 100 cm (39 in) |
| 4 × 3 m | 93 × 3 | 133 × 100 cm (52 × 39 in) |
| 4 × 4 m this page | 93 × 3 | 133 cm (52 in) |
| 5 × 4 m | 124 × 3 | 125 × 133 cm (49 × 52 in) |
| 6 × 4 m | 155 × 3 | 120 × 133 cm (47 × 52 in) |
| 6 × 5 m | 205 × 4 | 120 × 125 cm (47 × 49 in) |
Change the numbers
Your sizes will differ. The room lighting calculator opens with these numbers filled in: change any of them and the answer, the working and the drawing follow.
Editorial notes
Worked out by the Snuug team on 12 November 2026 with the same code as the room lighting calculator, so the two cannot disagree. Every rule cites its source, with the date we last checked it. A rule designers use is a convention, not a study.
Other sources the calculator draws on:
- Spear Lighting, Technical section: residential lux levels from SLL LG9 (2013), BS EN 12464-1 and HSG38; office lux levels (catalogue pages 388–391, PDF of 18 Sep 2020), checked 31 October 2026
- CIBSE, SLL LG9 Lighting for communal residential buildings (2022 edition; paywalled, not read), checked 31 October 2026
- CIBSE Code for Interior Lighting (1994), hotel table as reproduced on SlideShare (bedroom 50–100, kitchen 150–300 lux), checked 31 October 2026
- electricaltechnology.org, Lighting design calculation in a building, step by step (lumen method; UF 0.66 at room index 1.8 with 70/50/20 reflectances), checked 31 October 2026
- Emily Henderson, 19 lighting combos and rules (at least 2–3 light sources, at 2 or more heights), checked 15 October 2026
- Commission Regulation (EU) 2019/2020, equivalence claims for non-directional light sources (470 lm = 40 W, 806 lm = 60 W, 1055 lm = 75 W, 1521 lm = 100 W), checked 31 October 2026
- BLT Direct (7 May 2026), What is the difference between warm white, cool white and daylight LEDs?, checked 31 October 2026