Reading Performance is Affected by Light Level and Lamp Spectrum

摘要

This study examines the hypothesis that ambient light from typical fluorescent lamps but with relatively higher bluish color content (higher CCT), improves reading performance as defined by speed and accuracy when compared to lower CCT lighting. In particular, the study examines this hypothesis at light levels and print sizes that are found in modern offices (200 to 500 lux horizontal, 6 point to 12 point type) using 865 and 830 lamps for the high and low CCT (or high and low S/P value), respectively. Performance is studied under two different fixture types (pendant indirect and recessed parabolic fixtures) and at 3 different light levels differing by increments of 24%. Forty-seven subjects with ages ranging from 18 to 49 were divided into 3 separate age groups, each of which included roughly equal numbers of males and females. Each subject performed a visual task of reading out loud 2-digit numbers with constant size and a range of contrasts (possible values from 0.1 to 0.4). The task was adjusted for each subject to produce a significant difference in reading performance between the highest contrast at the highest light level and the lowest contrast at the lowest light level. The results show that reading performance (combined speed and accuracy) is affected by both spectrum and light level. There is a trade-off between light level and spectrum such that a higher CCT lamp can provide the same reading performance at a lower light level than a lower CCT lamp at a relatively higher light level, at light levels typical of commercial interior lighting. The effect occurs for both pendant indirect and recessed parabolic lighting. Measurements of pupil size support, as the dominant mechanism, the combined effect of light level and spectrum on reading performance.