# How many downlights do I need?

Sheet 10 · Lighting, whichfits.uk. A Markdown copy of https://whichfits.uk/how-many-downlights. The page itself has the working form and the Amazon.co.uk links: link to the page, not to this copy.

The electrician says six. The man in the lighting shop says nine, and he would. The forum says four, under a photo of a kitchen you can’t see the corners of. None of them has measured your ceiling. Downlights are a sum, and not a hard one: how much light the room wants, which the lighting trade writes down in lux, times the floor, divided by what one fitting puts out, which is printed on the box in lumens. Then a second sum, about spacing, so the light lands on the floor evenly instead of in a row of bright puddles with dusk in between.

Put the room in. The sheet gives you the count, lays the fittings out in a grid with the distances to the walls, and tells you when the spacing has gone wide enough that you’ll see the gaps.

## Work it out

Worked example, with the inputs the sheet opens on:

- What the room is: Kitchen
- Length (m): 4
- Width (m): 3
- Ceiling height (m): 2.4
- Lumens per downlight: 400 lm: an Integral 3.6 W GU10 bulb (50 W equivalent) in a GU10 fitting

**12 downlights**

12.0 square metres of kitchen at 300 lux wants about 3,600 lumens on the floor, which is 4,500 from the fittings once they have aged a few years, and at 400 lumens a fitting that is 12: a 3 by 4 grid, 1.00 m apart along the room and 1.00 m across it, with the outer ones 0.50 m and 0.50 m in from the walls.

That is close enough to the trade’s spacing rule for even light (half the ceiling height apart, 1.20 m here) for the ceiling to light evenly, with no dark corners.

Get fire-rated GU10 downlight fittings, a pack of 6 on Amazon.co.uk

Get Philips GU10 LED bulbs, a pack of 6 on Amazon.co.uk

### Lux by room, the figures the sheet uses

| Room | Lux | Lumens on the floor, 12 m² | Fittings at 400 lm |
| --- | --- | --- | --- |
| Living room | 150 | 1,800 | 6 |
| Kitchen | 300 | 3,600 | 12 |
| Dining room | 200 | 2,400 | 8 |
| Bedroom | 100 | 1,200 | 4 |
| Bathroom | 200 | 2,400 | 8 |
| Hall, stairs or landing | 100 | 1,200 | 4 |
| Home office | 400 | 4,800 | 15 |

Lux is lumens per square metre on the floor or the worktop. The figures are the recommended maintained illuminances for homes as the documents in the sources box give them; a kitchen worktop under the units wants more than the room, which is what under-cabinet strips are for. The fittings column divides by the 0.8 maintenance factor first, as the calculator does.

## Lux, lumens and the thing on the box

Lux is lumens per square metre landing on the floor or the worktop: the light that arrives, where lumens are the light that leaves the fitting. The guidance for homes, which Collingwood, a UK maker, publishes with a nod to CIBSE’s figures, puts a living room at 100 to 200 lux, a bedroom the same, a kitchen at 300 to 500 with the worktop wanting more again, a bathroom at 200 to 300, a hall or landing at 100 to 150 and a study at 400 to 500. The sheet takes the lower figure in each range, and the middle one for a living room, because a downlight count is a floor you can always put a lamp on top of, and a living room lit to 200 lux from the ceiling looks like a dentist’s waiting room.

The box prints lumens, and that is the number. Ignore the watts beside it and ignore the ‘50 W equivalent’: a 4.6 W GU10 bulb that gives 370 lumens and a 7.5 W integrated fitting that gives 650 are both downlights, and one gives nearly twice the light of the other. Count in lumens or you’ll count wrong.

## Half the ceiling height apart

The rule the British trade uses: space the downlights at half the ceiling height, so 1.2 metres apart under a 2.4 metre ceiling, and put the first row half that in from the wall, about 60 centimetres. Closer to the wall and the beam scallops the paintwork; further apart than the rule and you’re back to the puddles. ERCO, a German maker that lights galleries for a living, allows up to one and a half times the height above the worktop between fittings for even general light, roughly twice the trade’s distance, so the trade’s rule has slack in it. The sheet uses the trade’s figure as its check and says when the count from the lux comes out wider than that. When it does, the fix is not more light, it’s more fittings with less light in each: eight at 460 lumens beat four at 820.

## The sum, and the quarter it adds

Lux times square metres is lumens. Divide by the lumens of one fitting and round up. That is the whole method the retail calculators use, and it is the lighting engineers’ lumen method with two factors left out. The sheet puts one back. An LED fitting dims as it ages and dust settles on it, so the engineers design to a maintenance factor, the share of the first day’s light the room will still get years on, and a maker’s own worked example for an LED fitting in a clean room comes out at 0.8. The sheet divides by it, so the count is for the kitchen in five years, not for the afternoon the electrician leaves. The other factor, how much of the light reaches the floor rather than the walls, the sheet leaves at one: a downlight points down, and most of it does. Dark walls, a high ceiling or a narrow beam all eat some, so if you are between two counts, take the higher.

## Fire rated, bathroom rated, and which kind to buy

A downlight is a hole cut in a ceiling, and the ceiling was doing a job: holding a fire back long enough for the people upstairs to get out. A fire-rated fitting has a lining that swells and seals the hole when it gets hot, putting back what the hole took away, and under a floor with rooms above it that is the fitting to buy, whatever it costs over the plain one. In a bathroom, a fitting over the bath or in the shower needs a rating against water as well; the box gives the IP rating and says which zones it may go in, and if it doesn’t say, it isn’t going in there.

Then the only real choice. A GU10 fitting takes a bulb you can change in thirty seconds for the rest of the ceiling’s life. An integrated fitting is slimmer, often brighter for the same hole, and comes out whole when it dies, which is years away but is the whole fitting. Buy the GU10 kind unless the ceiling void is too shallow for it, or you want the most light from the smallest hole.

## Where to get it

- Get fire-rated GU10 downlight fittings, a pack of 6 on Amazon.co.uk. The fitting takes a GU10 bulb, so when the bulb goes you change the bulb, not the ceiling.
- Get Philips GU10 LED bulbs, a pack of 6 on Amazon.co.uk. Warm white for a living room or bedroom, cool white for a kitchen or bathroom.
- Get integrated LED fire-rated downlights, a pack of 6 on Amazon.co.uk. Slimmer and brighter for the hole, and the whole fitting comes out when it dies.

Those links go to Amazon.co.uk and earn this site a commission if you buy. The price is the same either way, and nothing on this sheet changes because of it.

## Where the numbers come from

1. [Downlights: how to get the lighting levels in a home right](https://www.collingwoodlighting.com/downlights-how-to-get-the-lighting-levels-in-a-home-right/), Collingwood Lighting. Living room 100 to 200 lux, kitchen 300 to 500 (worktop 500 to 700), bathroom 200 to 300, bedroom 100 to 200, hallway or landing 100 to 150, office or study 400 to 500, given as a starting point from CIBSE’s guidance (read 17 October 2026)
2. [Building standards technical handbook 2019: domestic, section 4.6 Electrical fixtures](https://www.gov.scot/publications/building-standards-technical-handbook-2019-domestic/4-safety/4-6-electrical-fixtures/), Scottish Government. Common areas: not less than 100 lux at floor level on stair flights and landings, 50 lux elsewhere in circulation areas; lists the CIBSE Code for Lighting among its references (read 17 October 2026)
3. [Lighting requirements in residential and commercial settings](https://www.ledvance.com/en-us/professional-lighting/insights/blog/sustainability/lighting-requirements-in-residential-and-commercial-settings), LEDVANCE. Formal dining room 200 lux, informal dining 100; an American page in footcandles, the only maker found that gives a dining room figure (read 17 October 2026)
4. [LED downlight spacing guide](https://www.simplelighting.co.uk/blog/downlight-spacing-guide), Simple Lighting (a retailer). Ceiling height divided by two: a 2.4 m ceiling, downlights about 1.2 m apart, about 60 cm from the walls (read 17 October 2026)
5. [Recessed downlights: planning the perfect layout](https://blog.lyco.co.uk/blog/recessed-downlights-planning-the-perfect-layout/), Lyco (a retailer). Dividing the ceiling height by two gauges the spacing; a living room needs only 150 to 200 lux, a worktop at least 300 (read 17 October 2026)
6. [Arranging luminaires: rules of thumb for the ideal luminaire spacing](https://www.erco.com/en_us/designing-with-light/lighting-knowledge/lighting-design/arranging-luminaires-7645), ERCO. For uniform general lighting the spacing between two downlights may be up to 1.5 times the height of the luminaire above the working plane; half the spacing to the wall (read 17 October 2026)
7. [Maintenance: planning and calculation tips](https://www.fagerhult.com/knowledge-hub/planning-and-calculation-tips/maintenance/), Fagerhult. Worked example for an LED luminaire with L90 in a clean environment: 0.9 × 1 × 0.94 × 0.95 = 0.8 (read 17 October 2026)
8. [Technical: lighting design guide (lumen method, utilisation and maintenance factors)](https://intranet.ee.ucl.ac.uk/facilities/teaching-lab/lighting.pdf), Cooper Lighting, catalogue pages hosted by UCL. E = F × n × N × MF × UF / A; illumination levels are in BS EN 12464-1 and the Society of Light and Lighting’s Code for Lighting, stated as maintained illuminance (read 17 October 2026)
9. [CorePro LEDspot 4.6-50W GU10 830 36D](https://www.signify.com/en-gb/prof/led-lamps-and-tubes/led-spots/philips-corepro-led-spot-mv/929001218102_EU/product), Signify (Philips). 4.6 W, 370 lm, 3000 K, 36 degree beam, 50 W equivalent; the 2700 K version is 355 lm and the 4000 K 390 lm (read 17 October 2026)
10. [GU10 bulb 400 lm 3.6 W 2700 K dimmable 36 beam (ILGU10DC109)](https://integral-led.com/en/product/light-bulbs-gu10/gu10-bulb-400lm-36w-2700k-dimmable-36-beam-integral--ILGU10DC109), Integral LED. 3.6 W, 400 lm (345 useful lumens), 50 W equivalent (read 17 October 2026)
11. [H2 Lite datasheet (DLT388, updated for 2023)](https://assets.cef.co.uk/downloads/pdg/collingwood_dlt388blk5530_datasheet/collingwood_dlt388blk5530_datasheet.pdf), Collingwood Lighting, hosted by CEF. 4.3 W, 460 lm at 3000 K and 490 lm at 4000 K, 55 degree beam (read 17 October 2026)
12. [H2 Lite 500 datasheet (DLT469)](https://cdn.yesss.co.uk/documents/1536951_03_DLT469MW6030_Datasheet_48cab5bafc165cf1adee1ede14468b2d.pdf), Collingwood Lighting, hosted by YESSS. 5 W, 500 lm, 100 lm/W, 60 degree beam (read 17 October 2026)
13. [Prism Pro Mini CCT fire rated downlight](https://ansell-lighting.com/en/products/prism-pro-mini-cct-fire-rated-downlight), Ansell Lighting. 5 W, 450 lm at 4000 K, 60 degree beam (read 17 October 2026)
14. [JC1001/WH V50 fire-rated LED downlight 7.5 W 650 lm IP65 datasheet](https://www.downlights.co.uk/media/catalog/product/d/a/datasheet__jc1001-wh___28-jan-2023_.pdf), JCC Lighting, hosted by downlights.co.uk. 7.5 W circuit wattage, 600/650 lm, 60 degree beam (read 17 October 2026)
15. [Prism Pro XM fire rated downlight](https://ansell-lighting.com/en/products/prism-pro-xm-fire-rated-downlight), Ansell Lighting. Up to 820 lm at 4000 K, power selectable between two outputs, 60 degree beam (read 17 October 2026)

Data on this sheet last changed 17 October 2026.

**Other sheets**

- Sheet 12 [How bright is 800 lumens?](https://whichfits.uk/lumens-to-watts)
- Sheet 11 [Which bulb fits this lamp?](https://whichfits.uk/which-bulb-fits)
- Sheet 13 [How many fairy lights do I need for my tree?](https://whichfits.uk/fairy-lights-for-a-tree)

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whichfits.uk is written and published by Jaco Olwagen, with software doing the sums. Links to Amazon.co.uk earn the site a commission if you buy something, and that is how the lights stay on. Nothing here is bought, tested or handled: every number on every sheet comes from the documents named at the foot of that sheet, with the date they were read.