How many downlights does your room need?

How many: one downlight per patch of floor

Lighting designers work in lux — the amount of light landing on each square metre. UK guidance suggests roughly 150–200 lux for relaxed rooms and 300+ lux for kitchens, bathrooms and workspaces. With a typical 500–600 lumen LED downlight, that translates into a simple density: one fitting per so-many square metres, tighter in hard-working rooms.

The calculator multiplies your room's area by the density for your room type, then rounds up — because a slightly brighter room with a dimmer beats a permanently gloomy one.

Where they go: an even grid, held back from the walls

The calculator then tries every sensible grid arrangement for that count and picks the one with the most even, most square spacing. Fittings are inset from the walls by about half the fitting-to-fitting distance — the industry rule that prevents harsh bright scallops running down your walls and stops the room edges falling into shadow. On a standard 2.4m ceiling this lands close to the electrician's rule of thumb: downlights spaced at roughly ceiling height ÷ 2.

Beam angle: matched to your ceiling height

Light spreads as it falls, so ceiling height changes which beam angle gives even coverage. The calculator starts from the right beam for your room type — wider (about 60°) for kitchens and bathrooms where even wall-to-wall coverage matters, tighter (about 45°) for living rooms and bedrooms where softer pools of light feel better — then adjusts the suggestion for your ceiling height.

The spec reminders: safety built into the answer

Alongside the layout, the calculator flags what your room type needs: fire-rated fittings as the default everywhere, IP65 for bathrooms, and anti-glare designs where you'll be relaxing or looking up. These match the advice in our fire-rating and bathroom zones guides.