How to use the lighting calculator
- Choose the room. A typical target light level is filled in; change it if you want the room brighter or softer.
- Enter the room’s length, width and ceiling height, and pick how light the walls and floor are.
- Enter the lumens of the bulb or downlight you plan to use, from its packaging.
- Read how many you need and the layout for downlights, then print the plan.
How the estimate is worked out
- Floor area = length × width.
- Light needed = target lux × floor area in m², then increased for darker rooms (× 1.2 for mid, × 1.5 for dark) and higher ceilings (× 1.15 above 2.6 m, × 1.3 above 3 m).
- Bulbs = light needed ÷ lumens per bulb, rounded up.
- Layout: the lights are spread in an even grid with rows and columns in proportion to the room. Each sits in the middle of an equal cell, so the gap to the wall is half the gap between lights.
Worked example
A living room 4 × 3.5 m with light walls and a 2.4 m ceiling, aiming for 150 lux, using 800-lumen bulbs.
- Floor area: 14 m².
- Light needed: 150 × 14 = 2,100 lumens (no allowances for a light room with a standard ceiling).
- 2,100 ÷ 800 = 2.6, so 3 bulbs, giving 2,400 lumens, about 171 lux.
Choose Try an example above (with metric selected) to load these numbers.
Tips for a bright, comfortable room
- Layer the light: general light from the ceiling, task light where you read, cook or work, and lamps for a softer evening mood.
- Fit dimmers (with dimmable bulbs) so a room can be bright for cleaning and soft for relaxing.
- Keep the colour temperature the same within a room so lights don’t look mismatched.
- Pale walls and ceilings bounce light around, so the same bulbs make a light room brighter than a dark one.
Assumptions and limitations
- This is a rule of thumb for general home lighting, not a professional lighting design. It assumes light is spread fairly evenly over the floor.
- The wall and ceiling allowances are simplified. Real results depend on each fitting’s beam angle, shades, and how clean bulbs and fittings are.
- Target light levels are typical values; guides differ, and people’s needs vary with age and task.
- Electrical work must follow local regulations; in many places fixed wiring should be done by a qualified electrician.
Frequently asked questions
What are lumens and lux?
Lumens measure how much light a bulb gives out; it’s printed on the box. Lux measures how much light lands on a surface: one lumen spread over one square metre. A foot-candle is one lumen per square foot, about 10.76 lux.
How many lumens is a 60 W bulb?
An LED sold as a replacement for an old 60 W incandescent bulb typically gives around 800 lumens. Roughly, 40 W equivalent is about 470 lumens, 75 W about 1100 and 100 W about 1600. Always use the lumens printed on the bulb you buy.
How far apart should downlights be?
For even light, a common rule is to space downlights about as far apart as the ceiling height, and half that distance from the walls. The planner spreads your lights in an even grid this way. Fittings with a narrow beam need to be closer together; check the beam angle on the fitting.
Is the target light level a rule?
No. The starting values are typical figures for general lighting in homes, and different guides quote different ranges. Older eyes usually need more light, and many people prefer less for relaxing. Change the target to suit you, and use dimmers so one room can do both.
Does this work for LED strips or lamps?
Yes, as long as you know their lumens. For a strip, multiply the lumens per metre by its length and enter that as one fitting. Lamps that light the ceiling or walls spread light differently from downlights, so treat the result as a guide.
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