The difference between lux, lumen and luminance
- Lumen (lm): The total amount of light emitted by a source; it shows how much light a luminaire produces.
- Lux (lx): The amount of light falling on a surface; 1 lx is 1 lm falling on an area of 1 m². Footpaths and squares are designed in lux.
- Luminance (cd/m²): How bright a surface appears to the eye; as it reflects the driver's perception on roads for motorised traffic, M classes are defined by luminance.
P classes: footpaths, parks, residential complex roads
P classes are for low-speed areas used by pedestrians and cyclists. The values are horizontal illuminance levels; they indicate the average and minimum values that must be maintained, taking maintenance into account.
| Class | Average illuminance | Minimum illuminance | Typical application |
|---|---|---|---|
| P1 | 15 lx | 3 lx | Heavily used city square, shopping area |
| P2 | 10 lx | 2 lx | City park, busy pedestrian route |
| P3 | 7.5 lx | 1.5 lx | Residential complex road, park path |
| P4 | 5 lx | 1 lx | Walkway, neighbourhood road |
| P5 | 3 lx | 0.6 lx | Little-used footpath |
| P6 | 2 lx | 0.4 lx | Very little-used area |
M classes: roads for motorised traffic
M classes are defined by the average road surface luminance, based on how the driver sees the road surface. The class is selected according to speed, traffic volume, junction frequency and the presence of pedestrians.
| Class | Average luminance | Typical application |
|---|---|---|
| M1 | 2.0 cd/m² | High-speed roads with heavy traffic |
| M2 | 1.5 cd/m² | Main arterial roads |
| M3 | 1.0 cd/m² | Main urban roads |
| M4 | 0.75 cd/m² | Streets and boulevards |
| M5 | 0.5 cd/m² | Collector roads |
| M6 | 0.3 cd/m² | Low-traffic roads |
C classes: junctions and conflict areas
Areas where different road users meet, such as junctions, roundabouts, pedestrian crossings and car park entrances, are designed using C classes, according to the average illuminance level.
| Class | Average illuminance |
|---|---|
| C0 | 50 lx |
| C1 | 30 lx |
| C2 | 20 lx |
| C3 | 15 lx |
| C4 | 10 lx |
| C5 | 7.5 lx |
Why does uniformity matter?
How evenly the light is distributed across the area matters as much as the average value. Uniformity (U0) is the ratio of the minimum value to the average. On a road with low uniformity, the eye has to keep adapting between bright and dark zones, which reduces comfort and safety. Correct pole spacing and the right choice of optics are the main factors that determine uniformity.
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