VISUAL PERFORMANCE AND VISUAL CLARITY UNDER ELECTRIC LIGHT-SOURCES - PART II - VISUAL CLARITY

This study investigates the subjective rating of visual clarity under five different light sources designed for commercial spaces. The speci fic lamps land manufacturer listed color properties) used were: (I) co ol white fluorescent, color rendering index (CRI): 62, correlated colo r temperature (CCT): 4100 K; (2) an energy efficient tri-phosphor fluo rescent, CRI: 82, CCT: 4100 K; (3) a high grade halophosphor fluoresce nt, CRT: 91, CCT: 5000 K; (4) a clear metal halide, CRI; 60, CCT: 4200 K; and (5) a white high pressure sodium, CRI: 80, CCT: 2700 K. Subjec ts used a seven-point semantic differential (S- D) rating scale to eva luate a scene which consisted of(1) the walls in their field of view; (2) a number of colorful objects on a table in front of them; (3) the desk at which they sat; and (4) the paper upon which their responses w ere made. Additional paired brightness comparisons (for equal illumina nce levels) were made between the sources. The tests were conducted in a typical small office. The lamps were located behind a simulated 2 x 4 ft lensed fluorescent troffer. Illuminance levels were held constan t at 538 lx (50 fc) on the response sheet, and 323 vertical Ix (30 fc) directly above the visual clarity scene 2.13 m (7 ft) in front of the subject. In addition, luminance distributions in the room were consis tent between light sources. Analyses of variance and followup tests we re used to compare the mean SD ratings of the sources. Tri-phosphor an d high grade halophosphor lamps were consistently scored on the positi ve end of the scales, and were rated better than cool white in terms o f clearness, brightness, and colorfulness on the SD scales.