UGR on Site Against UGR in the Model

Unified Glare Rating is calculated for an observer at a defined position looking in a defined direction in a room of uniform reflectance. Real occupants sit off the grid, look at a monitor rather than down the room, and work in spaces where a dark bookcase or a glazed wall breaks the reflectance assumption completely. We have been logging luminance-camera measurements against modelled UGR on completed floors since early 2023, currently across nineteen spaces.

The pattern is consistent rather than dramatic. Where the model reported UGR 17 or 18, measured values at real seated positions ran between one and four points higher, and the outliers were almost all rooms with a high-reflectance floor or a large glazed elevation behind the observer. Nothing about that is a scandal; the calculation is doing exactly what it says. The problem is that a number under 19 is treated as a pass and closes the conversation before anybody looks up from the desk.

Our working response is to model the two worst orientations rather than the nominal one, to cap luminaire luminance above 65 degrees explicitly in the specification, and to carry a luminance camera to the first floor handover. It costs a day. It has twice caught a substituted diffuser that met the letter of the specification and produced a visible bright band across the ceiling at every desk in the row.