Visual acuity depends on the color temperature of the surround lighting

Results are reported here of three studies of near visual acuity (normal reading distance of about 18 inches) under conditions of separate task and surround lighting. The surround fluorescent lighting is either high (7500 CCT) or low (3500 CCT) color temperature. The participants in these studies were 118, 76 and 19 college students respectively. In order to provide separate task and surround lighting conditions, the visual task, either Snellen letters or words of varying size, rested on a small size light table backlit by incandescent lighting. A venetian blind arrangement, angled so as to not interfere with the task view, was utilized to prevent the task lighting from illuminating the surround walls. The surround lighting conditions were adjusted so that equal photopic illuminance was provided at the eye for the two color temperature lightings. Task luminance varied between about seven and 1000 Nits (cd/m(2)) [2.04 and 292 fL (cd/ft(2))] and illuminance in the plane of the subjects' eye varied between 10 and 275 lx (lm/m(2)) [1 and 27.5 fc (lm/ft(2))]. Field sampling of lighting conditions in a large building showed that, except for the lowest levels, the test conditions were inclusive of actual field lighting conditions. For all test lighting. conditions, acuity was significantly better for the high color temperature surround lighting as compared to the low color temperature surround. The data show that to obtain equality of visual acuity under the two different surround spectra requires at least 400 percent more task luminance when the surround lighting is provided by the low color temperature lighting as compared to the high color temperature lighting.