The time spent indoors under artificial (electric) lighting has continued to increase and currently amounts to up to 90% of the day. Light is the most important stimulus for the circadian rhythm and has, besides long-term effects, also a direct impact on emotional and physiological aspects such as sleepiness, alertness, or performance. This article presents the results of two studies investigating the acute effects of light during morning and early afternoon on people in a controlled office environment. Melanopically optimized lighting conditions, and a dose–response dependency are investigated, measuring cognitive performance, subjective sleepiness, and user preferences of the lighting scenarios as well as cardiac effort. The results show a dependency in subjective sleepiness ratings depending on light conditions and time of day. Further parameters did not show any statistical differences. The presented studies extend the findings of acute light effects during the day but are limited due to relatively small sample sizes.
Beck et al. (Wed,) studied this question.