Uniformity and room surfaces: beyond average lux
Identify dark patches, bright islands and the effect of surface reflections.
Average illuminance describes the mean across a calculation surface. It does not show whether darker patches occur between luminaires. Uniformity U₀ is one useful measure: minimum illuminance divided by average illuminance on the same surface. The required value depends on the task.
Brightness across the field of view matters too. A bright desk against a dark wall feels different from the same desk in balanced surroundings. Walls, ceilings and large furniture influence reflected light and should be considered before selecting luminaires.
Calculations need realistic reflectance assumptions. A scheme modelled with a bright ceiling cannot simply be transferred to a hall with dark structural surfaces. New shelving or major changes to finishes warrant a review. Increasing power may preserve an uneven pattern rather than solve it; different positions or optics can be more useful.
What to clarify for your project
- Define calculation areas and their boundaries.
- Use reflectance values that represent the actual room.
- Inspect dark patches and strong brightness contrasts.
Remember: Assess the average, the minimum and the appearance of the surrounding space together.