The difference in luminance can be calculated or measured as a relation between different surface luminances. The following luminance conditions are recommended for the workplace:
- The working area (inner field of vision) – immediate surroundings (the near field) 3:1.
- The working area (inner field of vision) – surroundings (adjacent walls within the field of vision) 5:1.
- The working area (inner field of vision) – periphery wall surfaces (background) 10:1.
Later studies, however, show that the luminance relationship between the working area and the normal field of view (ambient area = wall/ceiling) should be 2:1 with an illumination level in the working area of 500 lx. This approach pays consideration to the visual, emotional and biological effects or artificial light and requires that the vertical illumination in work premises should exceed 250 lx.
The latest edition of EN 12464-1 is the first time there has been a requirement for vertical illuminance and illuminance in the ceiling. There are also requirements regarding cylindrical illuminances. In the standard, the requirement for minimum average (mean) illuminance on the walls is a minimum of 50 lx, with a uniformity (min/avg) ≥ 0.1. For ceilings, the values should be at least 30 lx, with a uniformity (min/avg) ≥ 0.1
For premises such as offices, educational premises, medical treatment rooms and communications areas such as entrance halls, corridors and staircases, walls and ceilings will have to be of greater brightness. In these premises, a higher, maintained illuminance is recommended, and the main surfaces should have the following values:
- Walls – average (mean) illuminance at least 75 lx with uniformity ≥ 0.1.
- Ceilings – average (mean) illuminance at least 50 lx with uniformity ≥ 0.1.
In order to achieve good visual comfort within an area, the average luminance on the room’s walls, as a general rule, should not fall below 30 cd/m². It is normal practice to translate luminance conditions to relative illuminance, as illuminances are used as guide values in light planning. Nevertheless, in this context it should be pointed out that today’s computerised calculation programs allow the calculation and documentation of different luminances for room surfaces. The table below provides information about recommended relative illuminances between the workspace and room surfaces for a typical area.
Luminance conditions with indirect lighting
With indirect lighting the average luminance on the ceiling should not exceed 500 cd/m², with a maximum acceptable luminance of 1500 cd/m². The luminance transition should vary gradually across the surface being lit to avoid the lighting from being distracting and uneven. The luminance balance (Lmin/Lave) should not exceed 1:10.
For the background lighting on the walls the maximum luminance should be limited to 1000 cd/m².
However, studies show that, with a horizontal illuminance on the working area of 500 lx, a luminance on the ceiling of 250–500 lx is perceived as comfortable. Thus, the ratio between the ceiling and the working area should be 1:1 or 1:2. Meanwhile, studies also show that a 50–50 distribution of light from the luminaire if often preferred. By this is meant a luminaire with 50% direct light and 50 % indirect light.
High luminance monitors
High luminance monitors
L > 200 cd/m²
Medium luminance monitors
L < 200 cd/m2
(positive polarity and normal requirements
with respect to colour detail properties of the displayed information – as, for example, in an office, educational establishment, etc.)
|≤ 3000 cd/m2||≤ 1500 cd/m2|
(negative polarity and/or higher requirements with respect to colour detail properties of the displayed information – as, for example, for CAD work, inspection of colours, etc.)
|≤ 1500 cd/m2||≤ 1000 cd/m2|
|Note: High luminance monitors (Screen High State Luminance – see also ISO 9241-302) – describes the maximum luminance of the white surface of the screen that normally can be obtained from the manufacturer of the monitor.|
|Explanation: In the proposed new standard, higher luminance levels are accepted as indicated in the table above for luminaires in premises with high luminance monitors (bright monitors with a background luminance of more than 200 cd/m²). To find out the luminance of a monitor in the white part, use the suppliers’ stated values.|
|Window wall||> 0,6||0,3–0,6¹⁾|
|¹⁾ The values apply in daylight – without daylight the relative illuminance should not exceed 0.2 provided that the glazed surfaces do not have bright curtains.|