How many downlights per room, and where to put them

In short. Count downlights by lumens, not by watts: a living room or bedroom wants about 150 to 200 lumens per square metre of general light, a kitchen or bathroom about 300. Divide by the lumens of one downlight (800 to 1,000 for a typical 10 watt LED) and round to a number that lays out evenly. Space them about half the ceiling height apart and a quarter of the ceiling height from the walls, and put the lot on a dimmer.

How do I work out the number?

Measure the room and multiply length by width for square metres. Multiply by the lumens per square metre for the room type below. Divide by the lumens of the downlight you have chosen, which is printed on the box. Round to a number that makes a tidy pattern: four, six or nine.

• Living room, bedroom, hallway: 150 to 200 lumens per square metre.
• Dining: 150, with the pendant over the table doing the rest.
• Kitchen, bathroom, laundry: 300, with extra task light under cupboards or at the mirror.
• Study or workshop: 300 to 400.

Example: a 4 by 5 metre living room is 20 square metres; at 150 lumens that is 3,000 lumens; with 800-lumen downlights that is four fittings, not the twelve on the builder's plan.

Where should they go?

Half the ceiling height apart, a quarter of the ceiling height from the wall. On a 2.7 metre ceiling that is roughly 1.3 metres between fittings and 65 centimetres from the walls. Closer to the wall throws a hard scallop on it; farther apart leaves dark patches between pools. Put a fitting where light is needed, over the reading chair or the bench, before you fill in the pattern.

Which beam angle?

Wide beams (90 to 120 degrees) for general light on standard ceilings. Narrower beams (36 to 60 degrees) for high ceilings or to pick out a wall, a painting or a bench. Mixing a few narrow beams into a wide-beam layout is what makes a room look designed rather than lit.

Fewer and brighter, or more and dimmer?

Fewer, brighter fittings on a good dimmer. Every extra hole is a draught, an insulation gap and a thing to clean, and a grid of downlights makes a ceiling look like a shop. Add a pendant, a lamp or wall lights for the evening and run the downlights at 40 percent.

Where this fits at Cosmo

• LED downlights & ceiling lights at Cosmo
• Lighting design & advice at Cosmo
• Warm white vs cool white