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In lighting design, the lumen method, (also called zonal cavity method), is a simplified method to calculate the light level in a room. The method is a series of calculations that uses horizontal illuminance criteria to establish a uniform luminaire layout in a space.

Illuminance is calculated with the following formula: Lux [lx] = luminous flux [lm] / area [m2]. The illuminance is 1 lux if a luminous flux of 1 lumen falls uniformly on an area of 1 m². The further away the area is from the light source, the lower the illuminance.

As a handy rule of thumb, a sitting room or bedroom will generally require around 10-20 lumens per square foot, while a bathroom or kitchen will need a stronger level of lighting, at around 70-80 lumens per square foot. To work out the lumens you need, simply multiply the square footage of the room by this figure.

To determine the required lumens, you will need to multiply your room's square footage by your room foot-candle requirement. For example, a 100 sq. ft. living room, which needs 10-20 foot-candles, will need 1,000 - 2,000 lumens.

As a handy rule of thumb, a sitting room or bedroom will generally require around 10-20 lumens per square foot, while a bathroom or kitchen will need a stronger level of lighting, at around 70-80 lumens per square foot. To work out the lumens you need, simply multiply the square footage of the room by this figure.

A = a x b = total area in [m2] F = total flux of the individual luminaire in [lm] Fu = utilization factor.

For example, in a 3×3 meter room, a 48W 4500lm canopy light is installed. Applying the formula E=4500/3/3=500lux, it can meet the lighting needs of a normal room. If the room is used as a study room, a wattage of 72W or higher is required.

E = F x Q x MF / A E represents illumination or lux. F represents the average lumen value of the lamp. Q represents the number of lamps. MF represents the maintenance factor of the luminaire. A represents the surface area covered by the luminaire (in square meters)