In order to determine precisely the necessary number of LED spots per room there is a unit measuring the illuminance: lux. It is calculated as follows: lux = lm / m2 (lm = lumen, m2 = square meter). The lux makes it possible to determine the luminous flux received for a given unit of surface. Once the required number of lux is determined, you can simply reverse the previous formula to convert the number of lux to lumen (lm = lux x m2). Simply divide the total lumen needed for a room by the amount of lumen emitted by a spot to find the spot numbers per room.
For a home, the number of lux for optimal lighting will depend on the daily use of each room:

• Passage areas, corridors, stairs> 100 lux
• Cloakroom, kitchen, bathroom and shower room> 200 lux
• Library> 300 lux
• Writing, Reading, meeting room, conference room> 500 lux