Daylight and Productivity – A Field Study

Panel: Panel 8. Human and Social Dimensions of Energy Use: Understanding Markets and Demand

Authors:
Mariana G. Figueiro, Lighting Research Center, Rensselaer Polytechnic Institute
Mark S. Rea, Lighting Research Center, Rensselaer Polytechnic Institute
Anne C. Rea, Lighting Research Center, Rensselaer Polytechnic Institute
Richard G. Stevens, Univ. of Connecticut Health Center, Dept. of Community Medicine

Abstract

Although it is well documented that lighting controls in combination with daylighting in offices can save up to one-half the lighting energy in commercial buildings, the positive impacts of daylight on productivity, human health and well-being may be more compelling reasons to incorporate daylight into the design of buildings.

There is growing evidence that light can impact human circadian systems and that the light intensities and spectra needed to activate the circadian system are different from those needed to activate the visual system. Lack of bright light exposure during the day may result in disruption of the circadian system and lead to feelings of depression, poor sleep quality, lethargy, and even illness.

Based on these speculations, it was hypothesized that people working in interior offices would spend less time in their offices and would be less productive than a matched group of people in windowed offices.

This study looked into the occupancy rates, amount of time subjects spent on workrelated tasks, and electric lighting operation in daylighted and interior offices. The results showed no difference in occupancy, but people in windowed offices spent significantly more time (15%) on work-related tasks than people in interior offices. Regarding electric lighting operation, energy waste (lights on when office is unoccupied) in interior offices was greater (28% of the times observed) than in windowed offices (13% of the times observed). Energy savings (lights off when office is occupied) occurred only in windowed offices (18% of the times observed).