title: Photometry in the dark: time dependent visibility of low intensity light sources.
abstract: This paper aims at describing the perceived brightness of persistent luminescent materials for emergency signage. In case of emergency, typically, a fully light adapted person is left in the dark, except for the emergency sign. The available photometric models cannot describe visibility of such light source, as they do not consider the slow dark adaptation of the human eye. The model proposed here fully takes into account the shift from photopic to scotopic vision, the related shift in spectral sensitivity and the dark adaptation. The resulting metric is a 'visibility index' and preliminary tests show that it more realistically describes the perceived brightness of persistent luminescent materials than the common photometric standards.
authors.affiliation: LumiLab, Department of Solid State Sciences, Ghent University, Krijgslaan 281/S1, B-9000 Gent, Belgium. dirk.poelman@ugent.be
authors.forename: Dirk
authors.initials: D
authors.lastname: Poelman
authors.forename: Philippe F
authors.initials: PF
authors.lastname: Smet
mesh_terms: D017076:Computer-Aided Design; D004056:Differential Threshold / Q000502:physiology*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D008029:Lighting / Q000295:instrumentation*; D008123:Location Directories and Signs; D008954:Models, Biological; D010775:Photic Stimulation / Q000379:methods*; D010783:Photometry / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014796:Visual Perception / Q000502:physiology*