VISUAL PERFORMANCE AND VISUAL CLARITY UNDER ELECTRIC LIGHT-SOURCES .1. VISUAL PERFORMANCE

Recent trends in the design of office lighting have seen an increase i n energy-efficient light sources and light sources with improved color properties, specifically triphosphor and high grade halophosphor fluo rescent sources. Lamps with increased color properties are also becomi ng popular due to their potential for enhancing worker performance. Th is study evaluates visual performance, using a numerical verification task, for both a high contrast and a low-contrast task under five diff erent light sources: 1. cool-white fluorescent, color rendering index (CRI) = 62, correlated color temperature (CCT) 4100 K 2. energy-effici ent, triphosphor fluorescent, CRI 82, CCT = 4100 K 3. high-grade halop hosphor fluorescent, CRI = 91, CCT = 5000 K 4. clear metal halide, CRI = 60, CCT = 4200 K 5. white high pressure sodium (HPS) source, CRT = 80, CCT = 2700 K A subsequent study to be presented in a separate pape r will evaluate these same light sources from a visual clarity perspec tive. The tests were conducted in a room designed to represent a typic al small office The sources were located above what appeared to be two typical 2 by 4 ft lensed fluorescent troffers. Tasks were undertaken at 538 1x (50 fc), and luminance distributions in the room were consis tent among all light sources. Analyses of variance were used to analyz e the data. There was no significant difference in task performance du e to any of the light sources, but performance was significantly degra ded on the low-contrast task. From a positive perspective, the metal h alide and white HPS lamps, when generating the same illuminance and lu minance distribution as the fluorescent sources, do indeed generate st atistically equivalent performance. Further, it is extremely important to recognize that the equivalent performance seen with the triphospho r lamp is generated with far fewer watts, i.e., a much higher efficacy , than the standard fluorescent lamp. It should also be noted that the test used in this study was achromatic, and that further studies shou ld be undertaken for tasks of varying hues where spectral composition of the light sources might affect performance even at equivalent contr ast levels or improve contrast at the same illuminance. Such evaluatio ns will be conducted under similar circumstances in the subsequent stu dy.