Enter the length and width of the room, the ceiling height, the beam angle and the number of lumens per spotlight. The calculator works out how wide the pool of light from one spotlight is, how many spotlights you need along the length and the width for even light, the distance between the spotlights and to the wall, and an estimate of the average illuminance. For lighting a wall, it gives the distance from the wall and between the spotlights.
What does the calculator work out?
First you choose what you want to do: light a room evenly, or light a wall. Then you enter the dimensions of the room, the ceiling height, the height of the surface that needs even light (the floor or a working plane), the beam angle of the spotlight and the number of lumens per spotlight. You get:
- the width of the pool of light from one spotlight on that surface;
- the number of spotlights along the length and along the width, and the total;
- the distance between the spotlights and the distance to the wall;
- an estimate of the average illuminance in lux, to compare with the advice from the lumen calculator.
How does the tool work out number and spacing?
Pool of light. The beam angle is the angle within which the luminous intensity is still at least half of that in the centre of the beam; that is how the European ecodesign regulation 2019/2020 defines it. The width of the pool of light is 2 × h × tan(beam angle ÷ 2), with h the distance from the spotlight to the surface.
Number and spacing. Spotlights placed as far apart as the width of their pool of light add up at the edges to about as much light as in the centre. The tool divides the length and the width of the room by that width, rounds up and spaces the spotlights evenly. The distance to the wall is half the spacing.
Amount of light. Average illuminance ≈ number of spotlights × lumens per spotlight × utilisation factor ÷ floor area. The utilisation factor is the share of the light that lands on the surface; the tool uses 0.55 for a room with light walls, just like the lumen calculator, and lets you adjust it.
Lighting a wall. For arcs of light on the wall with ordinary spotlights, the tool works with 30 to 60 cm from the wall and a spacing of about twice that. For an evenly lit wall with wall washers, it follows the placement rule of the manufacturer ERCO: about a third of the ceiling height from the wall, and at most 1.3 times that distance between the fixtures.
Frequently asked questions
Where do I find the beam angle of a spotlight?
On the packaging or in the product details of the bulb or the fixture, in degrees. With a fixture that takes a separate GU10 bulb, the bulb determines the beam; the same spotlight can therefore shine narrower or wider with a different bulb.
Can I place the spotlights closer together than the tool indicates?
Yes. Closer together gives more even light and more lux, at the cost of more spotlights. Further apart than the width of the pool of light gives dark bands between the spotlights.
Why does the tool give so many spotlights with a narrow beam?
Because a narrow beam makes a small pool of light. Spotlights of 24 to 36 degrees are made for accents, not for lighting a whole room evenly. For general lighting, choose a wider beam or combine spotlights with other lights.
Does the tool also work for track spotlights?
For the pool of light and the spacing, yes. On a track the spotlights are in a single line; calculate with the distance between the track and the surface or wall you are lighting. See track lighting explained.
Sources
- Commission Regulation (EU) 2019/2020, Annex I (definition of beam angle), EUR-Lex (2019)
- Iku wandfluiter: productinformatie en plaatsingsregels, ERCO (2026)
- Küche: Licht für Arbeitsflächen und Essplatz, licht.de (ZVEI)
