Perception of lighting and brightness from HID light sources

Two experiments have been carried out to compare high-pressure sodium (HPS) lighting with fluorescent high-pressure mercury (MBF/U) lighting which it often replaces in industry. The first compares results in two identical rooms, one lit by each source in turn, the other lit by a variable tungsten-halogen lamp. Results show that on average the subjects would prefer 23% more illuminance on the room surfaces from the HPS lamp than from the MBF/U. The second experiment investigated the perceived brightness of HPS and MBF/U lamps, using an intermediate tungsten halogen lamp. From this it was found that the subjects perceived the MBF/U light to be almost twice as bright as the HPS light.