How many downlights do I need per room?

It depends on the room size, type, and the light output (lumens) of each fitting. As a rough guide: a 4m x 3m living room (12m²) at 150 lux needs approximately 4-6 LED downlights at 800 lumens each. A kitchen of the same size needs more — around 8-10 downlights — because kitchens require 300 lux for task lighting. Our calculator does the precise maths using the lumen method.

What lux level do I need for different rooms?

CIBSE (Chartered Institution of Building Services Engineers) recommends: kitchens 300 lux, living rooms 150 lux, bedrooms 100 lux, bathrooms 200 lux, home offices 500 lux, hallways 100 lux, and garages 300 lux. These are general lighting levels — task lighting (e.g., under-cabinet kitchen lights) provides additional illumination where needed.

What is the lumen method for calculating lighting?

The lumen method is: Total lumens = (Required lux x Room area) / (Utilisation factor x Maintenance factor). The utilisation factor (typically 0.5-0.7) accounts for how much light reaches the working plane. The maintenance factor (typically 0.8) accounts for light loss over time from dirt and lamp ageing. Divide the total lumens by the lumens per fitting to get the number of lights needed.

How far apart should downlights be spaced?

As a general rule, LED downlights should be spaced at a distance equal to or less than the ceiling height. For a 2.4m ceiling, spacing of 1.2m to 1.8m apart is typical. Edge fittings should be half the spacing distance from the wall. Our calculator provides exact spacing based on the number of fittings and room dimensions.

Do LED downlights use a lot of electricity?

No. LED downlights are very efficient — a typical 800 lumen LED downlight uses only 8-10 watts compared to 50 watts for an equivalent halogen GU10. A room with 6 LED downlights uses about 60W total, compared to 300W for halogens. This makes a significant difference on your electricity bill, especially across a whole house. Use our Electrical Load Calculator to see the total impact on your property's maximum demand.

Lighting Layout Calculator — How Many Downlights Do I Need?

How We Calculate This

This calculator uses the lumen method recommended by CIBSE (Chartered Institution of Building Services Engineers) to determine the number of light fittings required for a given room. It takes into account the room type, size, light fitting output, and standard correction factors.

The lumen method formula

Total lumens = (Lux × Area) ÷ (Utilisation Factor × Maintenance Factor)

Number of fittings = Total lumens ÷ Lumens per fitting

Factors used

Utilisation Factor (UF): 0.6 — typical for domestic rooms with light-coloured walls
Maintenance Factor (MF): 0.8 — accounts for dirt accumulation and lamp ageing

Recommended lux levels (CIBSE)

Kitchen: 300 lux
Living room: 150 lux
Bedroom: 100 lux
Bathroom: 200 lux
Home office: 500 lux
Hallway: 100 lux
Garage: 300 lux

The calculator also determines the optimal grid layout and spacing for even light distribution across the room.

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Last updated: February 2026

All calculations are estimates. Verify with your supplier.

Lighting Layout Calculator — Lux Levels by Room Type