Lighting: calculate the useful power and the number of bulbs

Method of calculating the required lighting power and the number of bulbs / light points. Examples in energy saving lighting

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Many people wonder about the recommended light output and the number of bulbs needed. The vagueness and commercial blahs being legion, here is a summary article of the sizing of the lighting of a room.

To begin with, you should know that the lighting power in Lux is a rather subjective quantity: some people will be content without problem with 80 lux in their living room while others will want 300!

Also the type of light (spectrum of lighting) plays a lot: a bulb in natural sunlight will give an impression of much more light while the lumens of the source are the same.

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Recommended lighting powers (high scale)

  • Stairs, basements, attics: 30 lux
  • Garages, hallway, utility room: lux 60
  • Kitchen, game room, lounge, dining room, local housework, waiting room: lux 250
  • Room, kitchen work and leisure, secretarial and lab: 500 lux
  • Entrance hall, shower room, bathroom, children's room, pantry: 720 lux
  • Reading, writing, crafts, homework, crafts, drawings, makeup: 750 lux
  • Architecture, accurate work, precise control, differentiate colors 7000 lux

Regulatory lighting powers according to wikipedia

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Examples of other common lighting powers (for comparison)

  • Sensitivity of a low level camera: 0,001 lux
  • Moonlit Night: 0,5 lux
  • Well-lit night street: 20 - 70 lux
  • Local life: 100 - 200 lux
  • Well-lit apartment: 200 - 400 lux
  • Work room: 200 - 3 lux
  • night stadium: 1 500 lux
  • Outside overcast sky 25 000 lux
  • Outdoors in direct sunlight: 50 000 100 000 to lux

The disparity of these values ​​confirms my first remark on the subjectivity of lighting.

Calculation method of lighting design

It's pretty simple.

- 1 Lux = 1 Lumens / m²
- With the surface of the room to be lit and the desired number of lux, you obtain a number of Lumens.
- By knowing the Lumens per bulb, you have the number of bulbs necessary to install and therefore of light points / wall lights / lights to install.

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