Visual Performance and Light Spectrum: The Inadequacy of Conventional Photometry

At light levels typical of building interiors it is the optical quality of the eye rather than retinal illumination that limits visual acuity and contrast sensitivity. Because aberrations generally occur in the eyes of the majority of the population and because smaller pupils reduce the defocusing effects of aberrations, pupil size becomes the major factor that light spectrum can control to influence visual performance. Our studies demonstrate that for conditions of full field of view and light levels typical of interior spaces, pupil size as measured by objective infrared pupilometry, is predominantly controlled by scotopic spectrum. We also demonstrate in a series of 10 separate studies with different subjects that pupil size is the ultimate factor in limiting acuity and contrast sensitivity at typical interior light levels. A large number of subjects are employed in these studies which take place under conditions of binocular viewing in a 2 m cubic room lit by a variety of fluorescent lamps.