Visit the Energy Systems Laboratory Homepage.
Daylighting: Measuring the Performance of Light Shelves and Occupant-Controlled Blinds on a Dimmed Lighting Systems
Loading...
Date
1998
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Energy Systems Laboratory (http://esl.tamu.edu)
Texas A&M University (http://www.tamu.edu)
Texas A&M University (http://www.tamu.edu)
Abstract
The design of a day lighted space is both an art and
a science. The biggest challenge facing the lighting
designer is to admit only as much light as necessary
and distribute it evenly throughout the space without
introducing glare or heat. In warm climates such as
Florida, it has become common practice in windowed
spaces to specify blinds and glazing with high
shading coefficients to control glare and minimize
heat gain. However, this practice reduces the
effectiveness of lighting systems that dim
automatically. Improved systems are needed to
capture natural daylight and distribute it uniformly
throughout a space while controlling heat gain and
glare. One such system is the light shelf. Light
shelves shade the space from direct sunlight and
reflect this sunlight onto the ceiling for a deeper and
more uniform distribution. While this is not a new
idea, little unbiased empirical data has been collected,
outside the laboratory, that compares the performance
(energy savings, uniformity, and level) of an
automatic daylighting system.
This study measures the effectiveness of light
shelves and manually controlled horizontal blinds in
an automatic daylighting system. Power consumption
and interior work-plane lighting levels were
compared in four essentially identical private offices.
Two offices were configured with an interior light
shelf, one with a white diffuse top surface and the
other with a specular surface. The third office had no
window treatment and the fourth office had horizontal
blinds, which were manually adjusted by the user.
All offices had two lamp fluorescent luminaires with
dimming ballasts (min. 20%) controlled by a ceiling
mounted photosensor. The study showed that
daytime savings ranged from 29% to 46%, with the
largest savings from the office with the light shelves.
The office with horizontal blinds showed the poor
savings (32%) and also the poorest light uniformity
and level.