A comparison of light sources for the petrochemical industry

Currently, the calibration of photometers is based on the spectral sensitivity of the eye with the field of view limited to only 2 degrees. However, lighting applications of interest in work environments are rarely confined to such small fractions of the visual field. New research shows that the eye spectral sensitivity is different when a full field of view is considered. The changes in spectral sensitivity in full field are due to the influence of rod photoreceptors which have been previously and erroneously viewed as being responsive only at extremely low light levels. The rod or scotopic response has been found to be the primary spectral response of the pupil at multiple light levels, varying from typical interior levels to lower outdoor levels, such as those found in a petrochemical facility at night. In addition, scotopically rich sources impact brightness perception. These results are important for lighting applications since different sources that produce equal amounts of light, as measured by a photometer, can generate very different scotopic outputs. Light sources which are scotopically enhanced, such as metal halide and triphosphor fluorescents, produce a smaller pupil, thereby improving vision. By choosing scotopically enhanced sources there is a potential for energy savings.