Room Lighting Requirement Calculator
Size a room's lighting from its area and its purpose — total lumens needed and how many bulbs it takes to get there.
What this room needs
This is general ambient lighting. Task spots — a desk, a hob, a mirror — want extra local light on top, and rooms with dark walls or high ceilings need more than the flat estimate.
From square metres to bulbs
Lighting a room well is really two questions: how bright should it be, and how much output does that take? The first is set by the task — a lounge is relaxed, a kitchen is working, a study is exacting — and lighting guidance turns each of those into a target illuminance in lux. The second is just multiplication: the lux target times the floor area gives the total lumens the space needs.
Once you know the lumens, dividing by the output of a realistic bulb tells you how many fittings to plan. Spreading that light over several sources gives softer, more even coverage than one harsh point, and leaves room to add task lights exactly where the fine work happens.
Frequently Asked Questions
How many lumens does a room need?
Multiply the floor area in square metres by the recommended illuminance in lux for the task: required lumens = area × lux. A 12 m² kitchen at 300 lux needs about 3,600 lumens of general light. Divide that by the output of one bulb to see how many bulbs or fittings to fit.
What lux level does each room need?
Common guidance: living rooms and bedrooms about 100–150 lux, dining rooms 150–200, kitchens and bathrooms around 300, and home offices, studies, and workshops 400–500 lux or more. Brighter tasks need brighter light, so a study is lit far more than a lounge.
How many bulbs should I use?
The calculator divides the total lumens needed by the output of a single bulb and rounds up. Spreading the light across several fittings usually looks better and more even than one very bright source, so aim for a few moderate bulbs rather than one blinding one.
Does ceiling height or wall colour matter?
Yes. Higher ceilings put the light further from the working plane, and dark walls absorb light instead of bouncing it around, so both mean you need more lumens than the flat area-based figure. Light, matte walls make a room feel brighter for the same output.
Is ambient lighting enough on its own?
Not always. This sizes the general ambient light for a room. Detailed tasks — chopping at a worktop, reading at a desk, a make-up mirror — want extra local task lighting on top, aimed where you actually need it.
Educational estimate for general ambient light. For code-compliant workplace lighting, follow a proper lighting design and the relevant standard.