Advancing the effective use of light for society and the environment.

Friday, October 3, 2003

Okay to dim your lights at work?
LRC studies how office workers detect and accept the dimming of lights.

Experimental setup to test the detection and acceptance of light reduction in offices.
Are office workers willing to have their lights dimmed to help reduce the demand on our nation’s electric grid? If so, how much can their lights be dimmed before they even notice?

Reducing the peak demand for lighting energy through a technique known as load shedding can be an effective method of load management. This is particularly true when demand for electricity approaches the capacity of the power supply system because these “peak demand” periods call upon smaller, more costly generators to be brought online.

“Lighting offers an opportunity to reduce short-term demand for electricity without impacting productivity and normal business activities,” says Dr. Yukio Akashi of the Lighting Research Center (LRC). “Lighting can be dimmed for a few hours to reduce the demand.” Dr. Akashi and LRC graduate student Jason Neches studied workers’ light level requirements with respect to dimming. Their paper, “Detectability and Acceptability of Illuminance Reduction for Load Shedding,” has been published in the Journal of the Illuminating Engineering Society of North America (IESNA).

Dr. Akashi’s team conducted two studies. A Memory Study addressed the question of whether people memorize a room’s initial illuminance level and how long this memory is maintained. A Dimming Curve study examined the effects of dimming curvature (how much and how fast lighting is dimmed) on a person’s detectability and acceptability of the dimmed lighting.

“Knowing the detectable range of illuminance reduction,” says Dr. Akashi, “is the first step in understanding occupants’ requirements.” Beyond their ability to detect the dimming process, he explains, we need to determine how much dimming they will accept while still performing their work productively.

The LRC studies demonstrated that if people do not witness the transient change, they cannot detect changes in illumination under 20% based solely on memory of the initial light level. They concluded that regardless of the task assigned to the test subjects, 50% of them could detect an illuminance change after about a 15% reduction from the initial level. Half of the subjects accepted a 40% reduction in illuminance, while more than three-fourths of the subjects accepted a 20% reduction. As for the speed of dimming, slow rates of change have little or no effect on detectability and acceptability of illuminance reduction.

“Before using these findings in lighting practice,” says Dr. Akashi, “we need to investigate whether initial illuminance levels may result in different sensitivity and acceptance to illuminance reduction.”

About the LRC

The Lighting Research Center (LRC) is part of Rensselaer Polytechnic Institute and is the leading university-based research center devoted to lighting. Founded in 1988, the Lighting Research Center has built an international reputation as a trusted and reliable source for objective information about lighting technologies, applications, and products. Its mission is to advance the effective use of light and create a positive legacy of change for society and the environment

© 2003 Rensselaer Polytechnic Institute, Troy, NY 12180 USA.

Rennselear Polytechnic Institute