# Degree of illuminance, reflection and luminance

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.

Building standing alone
Building in a village
Building in a small town
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