The degree of illuminance E [ lx ] and the degree of reflection of the surface ρ are included in the calculation of luminance L [ cd/m2 ] in accordance with the following formula:
L = E · ρ / π
The luminance and thus the effect of the illuminated building or memorial are influenced significantly by the degree of reflection, which is reduced through the accumulation of dirt. However, the effect of the dirt diminishes with the degree of darkness and roughness of the original material. The degree of illuminance must be adjusted accordingly in order to achieve the same luminance or the same perceptive impression.
The effect of the building is all the more impressive the more it stands out from the background. The illumination of a tower in the middle of an illuminated city requires a higher degree of illuminance than if the background of a building is dark, for example a castle standing alone in the landscape.
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Building standing alone
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Building in a village
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Building in a small town
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Building in a large city
The table shows the change in degrees of illuminance, depending on the surroundings of objects and the surface materials
Illuminated
surfaces | Reflection | Building
standing alone
Dark
surroundings | Building
in a village
Dark
surroundings | Building
in a small town
Medium
surroundings | Building
in a large city
Light
surroundings |
| | |
Luminance:
L = 5 cd/m2 |
Luminance:
L = 10 cd/m2 |
Luminance:
L = 15 cd/m2 |
Luminance:
L = 20 cd/m2 |
Coloured surfaces | |
Degree of illuminance required |
| White | 90% | 7.5 lx | 15 lx | 22.5 lx | 30 lx |
| Pastel | 60% | 15 lx | 30 lx | 45 lx | 60 lx |
| Grey | 40% | 30 lx | 60 lx | 90 lx | 120 lx |
| Dark colour | 10% | 90 lx | 180 lx | 270 lx | 360 lx |
Stone | |
Degree of illuminance required |
| Light stone, marble | 60% | 15 lx | 30 lx | 45 lx | 60 lx |
| Sandstone | 30% | 40 lx | 80 lx | 120 lx | 160 lx |
| Dark granite | 10% | 90 lx | 180 lx | 270 lx | 420 lx |
Brick | |
Degree of illuminance required |
| Light yellow brick | 60% | 20 lx | 40 lx | 60 lx | 80 lx |
| Light brown brick | 40% | 40 lx | 80 lx | 120 lx | 160 lx |
| Dark red brick | 10% | 100 lx | 200 lx | 320 lx | 420 lx |
Wood | |
Degree of illuminance required |
| Light birch | 60% | 20 lx | 40 lx | 60 lx | 80 lx |
| Dark oak | 20% | 80 lx | 160 lx | 240 lx | 320 lx |
Concrete | |
Degree of illuminance required |
| Light grey | 60% | 30 lx | 60 lx | 90 lx | 120 lx |
| Dark grey | 40% | 60 lx | 120 lx | 180 lx | 240 lx |
Metal | |
Degree of illuminance required |
| Natural aluminium | 60% | 30 lx | 60 lx | 80 lx | 120 lx |
| Galvanised steel | 40% | 60 lx | 120 lx | 180 lx | 240 lx |
| Rust-red iron | 20% | 100 lx | 200 lx | 300 lx | 400 lx |
Influence of reflection surfaces
Despite standardised illumination, the level of illumination may be felt to be too low, depending on the nature of the floor, wall and ceiling surfaces.
In public areas, standards for light planning are very helpful. However, the influence of the spatial conditions must not be neglected. Examples of this are a public hall, a public square and an inner-city main road. Lighting standards for the square and the hall are indicated in lux [ lx ], that is, the degree of illuminance. Standards for inner-city main roads are defined in luminance with candela per square metre [ cd/m2 ].
Public hall · 800 m2
For example, an average degree of illuminance of 200 lx applies for the public hall. Proceeding from an average room, the standard provides for clearly defined reflection properties of walls, ceilings and floors. If these parameters are changed, the standardised degree of illuminance remains constant at 200 lx. However, the impression of the room is completely different. The illumination level is felt to be too low. From the table it can be seen that the luminance falls to 50% of the initial value. In this case, we recommend raising the degree of illuminance by 100 lx to 300 lx. This way, the illumination in the room would be felt to be more pleasant.
| Degree of illuminance | 200 lx | 200 lx |
| | Light room | Dark room |
| Floor reflection | 20% | 10% |
| Wall reflection | 50% | 30% |
| Ceiling reflection | 70% | 50% |
Luminance |
12 cd/m2 |
6 cd/m2 |
| Our recommendation | ✓ | + 100 lx |
Public square · 2500 m2
The same largely applies for the space situation in the public square. The value for the degree of illuminance is estimated to be 10 lx. With light ground and a reflection of 30%, the luminance level reaches 1 cd/m2. If the reflection of the ground is reduced to 10%, and the standardised degree of illuminance remains at 10 lx, the luminance is only 0.35 cd/m2 . Here we recommend raising the degree of illuminance by 10 lx. This way, the lighting conditions on the square are considered to be more pleasant.
| Degree of illuminance | 10 lx | 10 lx |
| | Light ground | Dark ground |
| Floor reflection | 30% | 10% |
Luminance |
12 cd/m2 |
0.35 cd/m2 |
| Our recommendation | ✓ | + 10 lx |
Inner-city main road
As far as road lighting is concerned, the uniformity of the light on the carriageway and the related distances between the luminaires are interesting for the planners.
The standard specifies values for average luminance. The adjacent table shows the effects of light and dark road surfaces on the distances between luminaires. When the road surface is light ( C1 ), the luminaire spacing is 36 m. With dark road surfaces (C2), the distance is reduced by 10 m to 26 m. Over a distance of 1 km, this is 28 compared to 38 luminaires. The choice of road surface thus has a direct economic effect, which should not be neglected during planning.
| Luminance | 0.5 cd/m2 | 0.5 cd/m2 |
| | light road surface C1 | dark road surface C2 |
| Luminaire spacing | 36 m | 26 m |
| Luminaires over a distance of 1 km | 28 luminaires | 38 luminaires |
