Lux, Lumens, Square Metres: The Three Quantities of Lighting Planning
Every lamp packaging shows a lumen figure, and yet at first it helps you very little. That is because lumens describe only how much light a lamp gives off in total, whether it hangs in a storage cupboard or in a loft. Whether a room looks bright is decided by a different quantity: lux. Lux measures how much light actually arrives on a surface, and the definition is pleasantly uncomplicated. One lux corresponds to one lumen per square metre.
This very definition makes room planning so simple. If you know how many lux a room needs for its use and how big it is, you also know the lumen total your lamps must deliver together. There is no more to the formula of area times lux. You need neither a measuring device nor a professional planner, a tape measure and this article are enough.
One honest limitation does belong here, though: equating lux with lumens per square metre is a deliberate simplification. It assumes that the lamp's light arrives completely and evenly in the room. In reality, lampshades, dark walls and high ceilings swallow part of it. The results from this article should therefore be read as a lower limit, to which you add 20 to 30 per cent depending on the room. How many lumens an LED of a given wattage delivers is shown in our lumens to watts chart.
Lux Guideline Values by Room: The Chart
How bright a room should be depends on its task. In the living room you want to relax, in the kitchen you cut with sharp knives, at the desk you read small print for hours. The following guideline values are usual planning recommendations for private households; the value for the workplace is based on the recommendation for office workplaces:
| Room | Guideline value | Example area | Rough lumen total |
|---|---|---|---|
| Living room | 100 to 150 lx | 20 m² | 2,000 to 3,000 lm |
| Bedroom | ca. 100 lx | 14 m² | ca. 1400 lm |
| Hallway | ca. 100 lx | 6 m² | ca. 600 lm |
| Kitchen | 250 to 300 lx | 12 m² | 3,000 to 3,600 lm |
| Bathroom | ca. 250 lx | 8 m² | ca. 2000 lm |
| Home office workplace | ca. 500 lx | Work surface | General lighting plus desk lamp |
Two notes on reading the chart: the lumen total applies to the whole room, not to a single lamp. And the value for the workplace refers to the work surface, that is, the desk and keyboard. Nobody has to flood a whole study with 500 lux; how to make the desk bright in a targeted way is explained in our guide to eye-friendly working in the home office.
The Calculation: Area Times Lux Gives Lumens
The calculation itself is mental arithmetic. You measure the floor area of the room, choose the lux guideline value from the chart and multiply the two. Three examples show how quick it is:
- Living room, 20 square metres: 20 times 100 gives 2,000 lumens as a lower limit, 20 times 150 gives 3,000 lumens for bright everyday moments such as cleaning or games evenings. Planned as dimmable, you cover both situations with the same installation.
- Kitchen, 12 square metres: 12 times 250 gives 3,000 lumens, and with the upper guideline value of 300 lux it is 3,600 lumens. Part of that belongs directly over the worktop as under-cabinet lighting, where hands and knives would otherwise lie in their own shadow.
- Bedroom, 14 square metres: 14 times 100 gives 1,400 lumens. Here you may deviate generously downwards, because in the evening cosiness counts for more than brightness and you need the full total only for tidying up or packing a suitcase.
To translate the lumen total into specific lamps, a memory aid helps: around 806 lumens corresponds to the old 60-watt incandescent light bulb. The 2,500 lumens of a medium-sized living room are therefore about three classic light bulbs, as LEDs typically with 7 to 10 watts each according to manufacturer information. Which lamp holders, strengths and colour temperatures exist is sorted out by our buying guide to LED light bulbs.
And once more on the reserve, because in practice it makes the difference: anthracite-coloured walls, ceilings above three metres in older buildings and fabric shades can turn arithmetically sufficient lumens into a room that is noticeably too dark. In such rooms, add 20 to 30 per cent to the total. Too much light is no risk as long as the lamps are dimmable; too little light can be fixed afterwards only with new lamps.
Let the lighting calculator do the sums for you.
Choose a room, enter the area, done: the calculator converts the lux guideline values from this article into your personal lumen total and recommends the matching colour temperature at the same time.
Light Layers: General Lighting, Zone Lighting, Accent Lighting
The lumen total answers only the question of how much. Just as important is how it is distributed, and here lighting planners work with three layers. The general lighting makes the room usable as a whole and usually comes from above; it sensibly carries about half to two thirds of the calculated total. For this layer, ceiling lights are the first choice, preferably dimmable and with adjustable colour temperature.
The zone lighting picks out individual areas of the space: the reading corner, the dining table, the armchair by the window. Here floor lamps play out their strength, because they bring directed light exactly where you need it, without changing the whole room. A floor lamp with 400 to 800 lumens next to the sofa does not replace a ceiling light, but makes the evening considerably homelier than any middle-of-the-room solution.
The accent lighting, finally, is the smallest layer with the greatest effect on mood: a small lamp on the shelf, a spot on a picture, warm light behind the television. On paper it hardly counts, visually it gives the room depth. For all three layers, colour temperature helps decide whether the result feels cosy or sober. Which Kelvin figure belongs where is explained in our guide to colour temperature in Kelvin.
Common Planning Mistakes and How to Avoid Them
In lighting planning, most rooms fail not because of the maths but because of five recurring errors of thinking:
- One lamp is supposed to do everything: Producing the entire lumen total from a single ceiling light creates flat light with harsh shadows in the corners. Spread the total across at least two, better three, light sources.
- Lamp lumens confused with room lumens: A dense fabric shade or a downward-pointing spot brings only part of its rated lumens into the room. Do not count directed light and closed shades in full towards the total.
- Kitchen and bathroom planned too cosily: What is atmospheric in the living room is simply too dark at the cooker. Functional rooms need a good double of a living space, at 250 to 300 lux.
- 500 lux extrapolated to the whole study: This leads to absurd lumen figures and glaring brightness. The right approach is moderate general lighting plus a good desk lamp that supplies the work surface in a targeted way.
- Not planned as dimmable: A room needs a different brightness at seven in the morning than at eleven in the evening. Dimmable lamps turn a calculated lumen total into a range that you adapt to the situation.
Conclusion: Calculate First, Then Buy
The question of lumens per room is not a matter of taste but a calculation with a built-in safety margin. Area times lux guideline value gives the total, a reserve for dark walls and high ceilings is added on top, and the whole is distributed across general lighting, zone lighting and accents. Anyone who plans this way never buys a lamp twice and never again sits in a room that looks gloomy despite a new lamp. The most convenient start is our lighting calculator, which takes over the calculation including a colour temperature recommendation; you will then find the matching lamps for each layer in our buying guides.