The wrong metric is being optimised
Office lighting is still frequently specified by lux on the desk. But nobody complains that their desk is too dim — they complain about reflections, headaches and screens that look washed out. Those are glare problems, and lux does not measure them.
Understanding UGR
Unified Glare Rating models discomfort from bright sources in the field of view. UGR<19 is the working target for screen-based offices. It depends on the observer position, so a figure quoted without stating where it was calculated tells you very little.
Screen reflections
A bright luminaire reflected in a monitor is as disruptive as direct glare. Keeping luminance below 3000 cd/m² at angles above 65° from vertical addresses most of it, which is why microprismatic optics outperform bare opal diffusers in open-plan space.
A sensible specification
300–500 lux on the task plane, UGR<19 at seated positions, 90+ CRI, daylight-linked perimeter dimming and presence zoning by bay. That combination is comfortable, compliant and typically 30–40% below baseline energy allowances.
