Lighting quality recommendations for VDT offices: a new method of derivation

An experiment in a mock-up office space gave occupants control over dimmable lighting circuits after a day working under pseudo-random lighting conditions. Data analysis indicated that the lighting experienced during the day influenced the changes in lighting made at the end of the day. Occupants chose to reduce screen glare if any existed. Even after allowing for the effect of glare, desktop illuminance at day’s end varied with the illuminance experienced during the day. Regression of these end-of-day choices relative to the illuminance experienced during the day can yield a preferred illuminance, equivalent to the daytime illuminance at which no change was preferred at day’s end. Using this method, preferred illuminances in the range 200-500 lux were derived. Preferences for luminance ratio were also derived. Interestingly, the deviation between participants’ lighting preferences and the lighting they experienced during the day was a significant predictor of participant mood and satisfaction.