Uniformity Ratio (U0)

Uniformity ratio describes how evenly light is spread across a surface, most commonly as U0 = minimum lux ÷ average lux over the calculation grid. A warehouse aisle averaging 200 lx but dropping to 40 lx between fixtures has U0 = 0.2 — bright pools and dark gaps that force the eye to constantly re-adapt. Design standards set floors for it: EN 12464-1 typically asks for 0.4–0.6 on task areas, EN 13201 road classes specify overall and longitudinal uniformity, and sports standards go further for televised play. Uniformity is decided by layout, not wattage — fixture spacing versus mounting height and the beam’s distribution matter more than raw lumens, which is why a DIALux study checks U0 alongside average lux before a layout is signed off.