How to use the lux calculator
- Enter the length and width of the room (or of the area you want to light) in metres or feet.
- Pick the closest room or task to fill in a reference illuminance, or type your own target in lux.
- Leave the utilisation and maintenance factors at 1 for a quick minimum, or enter values from the light fitting’s datasheet or a lighting designer.
- Optionally enter the lumens of one light fitting to see how many fittings that takes.
Formula
The calculator uses the lumen method:
Φ = E × A ÷ (UF × MF)
- Φ: total luminous flux needed from all fittings, in lumens (lm)
- E: target average illuminance on the working plane, in lux (lx = lm/m²)
- A: area, in m² (feet are converted with 1 ft = 0.3048 m)
- UF: utilisation factor, the share of the lamps’ light that reaches the working plane
- MF: maintenance factor, the share of light left after lamps age and fittings get dirty
Number of fittings = Φ ÷ lumens per fitting, rounded up. The illuminance reached with that whole number of fittings is (fittings × lumens per fitting × UF × MF) ÷ A.
Units
Illuminance in lux (lx); 1 footcandle (fc) = 1 lm/ft² ≈ 10.764 lx. Light output in lumens (lm). Area in square metres (m²) or square feet (ft²).
Reference illuminance values
EN 12464-1 sets maintained illuminance values (Ēm) for workplaces. The “modified” value is the higher level the standard suggests when, for example, the task is visually demanding or the people doing it have reduced vision. These are the values offered in the calculator:
| Room or task | Required Ēm (lx) | Modified Ēm (lx) | Reproduced by |
|---|---|---|---|
| Circulation areas, corridors | 100 | 150 | Glamox |
| Washrooms, bathrooms, toilet areas | 200 | 300 | Glamox |
| Archiving | 200 | 300 | Signify code finder |
| Filing, copying | 300 | 500 | Signify code finder |
| Reception desk | 300 | 750 | Signify code finder |
| Writing, typing, reading, data processing | 500 | 1000 | Signify code finder |
| Conference and meeting rooms | 500 | 1000 | Signify code finder |
| Technical drawing | 750 | 1500 | Signify code finder |
The standard does not cover homes. For a room at home you can use a similar task as a reference (a desk for reading, for example, is close to “writing, typing, reading”) or set your own target.
Sources
- EN 12464-1, Light and lighting – Lighting of work places – Part 1: Indoor work places, office rows as reproduced in Signify’s “Performance in Lighting” code finder (edition not stated on that page; checked 15 October 2026)
- EN 12464-1:2021, educational premises table, as reproduced by Glamox (“Communal and circulation areas for education”, checked 15 October 2026)
- EN 12464-1:2021, as reproduced by Glamox (“Amenity and changing rooms”, checked 15 October 2026)
Limits of this calculator
- The result is an average over the whole area. The lumen method says nothing about how evenly the light is spread, glare or colour rendering, which the standard also sets requirements for.
- With UF and MF left at 1 the result is a lower bound: in a real room some light is absorbed by walls and ceiling, and output drops over time.
- The standard values are reproduced from the manufacturer pages listed above, not from the standard text. If you must comply with EN 12464-1, check the edition that applies to you and its full tables.
- It cannot measure the light in your room; only a calibrated lux meter can.