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Lighting Layout Calculator — Lux Levels by Room Type
Calculate how many lights you need and their spacing using the CIBSE lumen method and indicative lux levels for UK rooms. Supports LED downlights, panels, and fluorescent tubes.
Longest dimension of the room
Shortest dimension of the room
Proportion of light reaching the working plane (default 0.6)
Light loss over time from dirt and ageing (default 0.8)
Safety notice
Electrical work in dwellings can be notifiable under Part P of the Building Regulations. Treat these figures as planning guidance only: circuits must be designed, installed and certified to BS 7671 by a competent person, normally a registered electrician.
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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
Typical lux levels (indicative)
General-lighting targets derived from CIBSE Guide A (dwellings) and the SLL Code for Lighting. CIBSE publishes ranges for dwellings rather than a single fixed table, so these are indicative starting points — add task lighting where the activity needs it.
- Kitchen: 300 lux
- Living room: 150 lux
- Bedroom: 100 lux
- Bathroom: 150 lux
- Home office: 500 lux
- Hallway: 100 lux
- Garage / workshop: 300 lux
The calculator also determines an even rectangular grid layout and the spacing for uniform light distribution across the room. Where the lumen-method minimum does not fill a neat rectangle, it rounds the fitting count up to the next even grid.
Frequently Asked Questions
It depends on the room size, type, and the light output (lumens) of each fitting. As a rough guide using the lumen method: a 4m x 3m living room (12m²) at 150 lux needs about 5 LED downlights at 800 lumens each (rounded to an even 6-fitting grid). A kitchen of the same size needs more — about 10 downlights — because kitchens target 300 lux for task lighting. Our calculator does the precise maths and rounds the count up to an even rectangular grid for uniform spacing.
Typical general-lighting targets, derived from CIBSE Guide A (dwellings) and the SLL Code for Lighting, are: kitchens 300 lux, living rooms 150 lux, bedrooms 100 lux, bathrooms 150 lux, home offices 500 lux, hallways 100 lux, and garages/workshops 300 lux. CIBSE publishes ranges for dwellings rather than a single fixed table, so treat these as indicative. They are general lighting levels — task lighting (e.g., under-cabinet kitchen lights or a shaver/mirror light) provides additional illumination where needed. Use our Lux Level Calculator for detailed lux calculations based on room dimensions and fitting output.
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.
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.
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. Then check our Lighting Circuit Calculator to determine how many circuits you need.
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.