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

Tuesday, July 15, 2003

How bright is that room?

LRC is examining how we perceive room brightness.

How bright do you like a room to be lighted? People often prefer a room to be brightly illuminated, but as demands for energy savings increase, room brightness often decreases. Researchers at the LRC are examining how people perceive room brightness. This understanding could lead to improvements of the structures in which we live and work.

Dr. Yukio Akashi (pictured at right), in perceiving how brightly a room is illuminated, says our brain relies not only on the amount of light reaching our eyes, but also on specific brightness cues. “When we enter a room, we perceive how the room is illuminated, including the locations of light sources and the direction of the light, by taking into account certain cues such as light reflecting off various surfaces,” says Dr. Akashi. Shadows, shading, and highlights of objects suggest the direction of light, and the sparkle and glint of light sources suggest the light’s location. “These factors influence our perception of room brightness,” he adds.






To illustrate his point, Akashi points to a work of art that appears to be a plaster statue sitting on the edge of a picture frame. A space appearing behind the picture frame looks dark. A spotlight seems to be located above the statue, highlighting its form and casting shadows below. In reality, however, the plaster statue, the picture frame, and the shadows are all painted directly on the wall. The painted highlights and shadows successfully trick our perception.

“Interestingly,” says Dr. Akashi, “even after we realize we have been tricked, the illusion persists. So it is likely that these perceptual cues are sensually processed rather than cognitively processed.”

Akashi says cues about room brightness have been studied only in isolation, so he believes a more systematic approach will help to quantify the effects of brightness cues on lighting. Still unknown is whether brightness cues add together or interact with each other. "We should also demonstrate how to use those cues to enhance room brightness with minimal lighting energy in the real world.

The Lighting Research Center is conducting these important studies. Ultimately, an understanding of the mechanism contributing to brightness perception is important. In the meantime, however, Dr. Akashi says we need some practical outcomes to help in the creation of more energy-efficient lighting.

Click here to learn more about brightness perception and related topics.


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.

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