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
Area × lux is the light that must land; bulbs are rated for the light they emit, so the bulb lumens are that divided by the share that lands. 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 land a smaller share. The room lux presets are rule-of-thumb starting points for homes, not a standard.
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.
Bulbs are rated for the light they emit, not the light that lands, so divide by the share that reaches the working plane (about half or less in an ordinary room) before dividing by the output of a realistic bulb to see 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 target illuminance in lux: area × lux is the light that must land on the floor and worktops. A 12 m² kitchen at 300 lux needs 3,600 lumens to land. Bulbs are rated for the light they emit, and shades, walls and dust take a cut first, so divide by the share that lands: at half, that is 7,200 lumens of bulbs, or nine 800-lumen bulbs rather than five.
What lux level does each room need?
As rules of thumb for homes: 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. These are starting points, not a standard: EN 12464-1 sets maintained illuminance values for workplaces (not homes), and in North America the IES publishes recommendations by task. 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 bulb lumens needed (the light that must land, divided by the share that lands) 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 lower the share of bulb light that lands and mean more bulb lumens. Light, matte walls raise the share. The surest number is your own: hold a lux meter at worktop height, multiply the reading by the floor area, and divide by the room's total bulb lumens.
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.