Kitchen Downlight Calculator: How Many Do You Need?

Most kitchens end up with too few downlights in the wrong places, so you work in your own shadow at the worktop and stare at bright pools on the floor. This tool does the job the other way round: it works out the total light your kitchen needs, turns that into a number of fittings, a spacing in metres and a lumen output per fitting, and then sizes the under-cabinet lighting that lets you keep the ceiling lights soft. Buy on lumens, not watts: two fittings sold as the same wattage can differ by half again in the light they actually give.

How the numbers are worked out

The tool uses the lumen method, the same sum a lighting designer starts with. Your target light level in lux is multiplied by the floor area to give the light landing on the work plane, then divided by two efficiency factors: a utilisation factor, because only part of what a downlight emits reaches the worktop and the rest is lost to walls and ceiling, and a maintenance factor of 0.8, because fittings dim slightly and collect dust and cooking grease over their life. Kitchens are the dirtiest room in the house for light fittings, so designing to the clean, out-of-the-box figure leaves you short within a couple of years.

Utilisation falls as the ceiling gets higher, because the light has further to travel and more of it lands on the walls: the tool assumes 0.60 up to a 2.5m ceiling, 0.52 up to 3m and 0.45 above that. Dark walls and ceilings bounce much less light back, so the dark option cuts the utilisation factor by 15 per cent, which pushes the lumens you need up by about 18 per cent. These are typical planning values rather than a substitute for a manufacturer's utilisation table for the exact fitting you buy.

Spacing: the rule that stops scalloping

Once you know how many fittings you need, spacing decides whether the light looks even or like a row of spotlights. As a working rule, downlights should sit no further apart than about three quarters of the ceiling height, which is roughly 1.8m on a standard 2.4m ceiling, and the distance from a wall should be about half the spacing between fittings. Go wider than that and you get scallops of light on the walls with dim patches between them. The tool then lays the fittings out as an even grid inside that limit, and because a grid has to be a whole number of rows by a whole number of columns, and because spacing that roughly matches in both directions looks better than one sparse long row, it often lands one or two fittings above what the lumen total alone requires. When it does, use the lower per-fitting output it gives you rather than buying brighter lamps.

The number people get wrong: distance from the wall units

A plain grid drawn on the room puts the outer row of downlights over the tops of your wall cupboards, where the light does nothing except heat the cornice. Along any wall with units, pull that row out to roughly 0.75m from the wall face, so the beam clears a 600mm base unit and lands on the front edge of the worktop rather than behind your shoulders. That single adjustment removes most of the shadow people complain about after a refit. Keep the rest of the grid even, and set out from the finished unit line, not from the plasterboard.

Ceiling lights alone will not do it

No arrangement of downlights lights a worktop well, because you stand between the ceiling and the chopping board. Under-cabinet strips fix that for very little money: mounted at the front edge of the cupboard underside, close to the surface and shielded from your eye line, they need far less output than a ceiling fitting to reach a comfortable 500 lux on the worktop. The calculator sizes them at about 415 lumens per metre of run, which sits in the middle of what mains and 24V LED strip products offer. Over a range cooker the hood usually supplies its own task light, so check what it gives before adding more. Our cooker hood extractor size calculator sizes the hood itself, and the kitchen lighting guide covers the three layers and what to put where.

Before you order

• Match the colour temperature across every fitting. For a country kitchen, 2700K to 3000K warm white. Mixing 3000K downlights with 4000K strips under the cupboards is the most common and most visible mistake.
• Choose a wide beam for general light. Around 60 degrees spreads evenly; narrow 36 degree beams are for accenting a specific thing.
• Put the ceiling circuit on a dimmer and check the fittings are marked dimmable, with a trailing-edge dimmer rated for LED loads.
• Use fire-rated downlights wherever you cut into a ceiling that separates the kitchen from a room above, to restore the fire resistance you have just made a hole in.
• Get an electrician for a new circuit. A new lighting circuit is notifiable work under Part P in England and Wales, and the total load figure here is only a guide to what you are adding.