Global HomeBusiness >You are here:Eco Solutions >You are here:lighting > containsTechnology > containsLighting knowledge > containsThe light required for each room

The light required for each room

The light required in each room differs with the purpose of the room.
Instead of brightening the whole room, consider adding task light to gain brightness required.

Room activity and illuminance (an example of Japan’s recommended illuminance levels)

Partial illuminance is for task light, general illuminance is for ambient light.

The standard for brightness is the average illuminance of the floor surface as recommended in JIS Z9110-2010 (General rules of recommended lighting levels)Paragraph 5.10, Residence; Table 17, Living room (general).

*The Ra value (the general color rendering index) is a method for describing the effect of a light source on the color appearance of objects, compared to a reference source of the same color temperature.
The closer to 100 the better the color rendering properties.


Illuminance and the dispersion of light changes with the height of the ceiling.

Floor illuminance and range of half-illuminance of a 100W bulb equivalent focused downlight

* Direct floor illuminance is inversely proportional to the height of the ceiling (not counting reflection).
* The diameter of the illuminance on the floor surface is directly proportional to the height of the ceiling (ceiling height x 0.4).


Example of illuminance

Outside daylight on a clear day 100,000 lx
Night of a full moon 0.2 lx
On a living room table 200 to 300 lx
Office (on a desk) 700 to 1,000 lx

Terminology related to illuminance

Maintenance factor
Illuminance deteriorates over time due to reasons such as decline in luminous flux and dirty shades. The maintenance factor is a correction factor for securing the necessary illuminance even after a certain period of time.

The relation between brightness and distance from a light source (light fixture)

Brightness is inversely proportional to the square of the distance.

Brightness perception index (Feu)

“Feu” is the original index of brightness perception from one’s eyesight.
Feu is quantified by comprehensively taking into account the volume of light that enters the eyes from the ceiling, walls and floor in the field of view.

Guide to illuminance for a 100W type LED downlight

Ceiling height Average illuminance for a 20m2 space (Unit: Lux)
Upper line: average illuminance
Lower line: maximum illuminance
Number required
2.5m 118 5
2.8m 123 6
3.0m 117 6
3.2m 147 8
3.5m 136 8

(Calculation conditions for illuminance distribution)
Maintenance factor:1, Reflection: 70/50/30, Height of calculation surface: 0.4 m