Scientific literature has long supported the notion that reducing contrasts in perceived brightness between a visual display and its background will result in reduced visual fatigue and eyestrain. LRC researchers recently tested this hypothesis in the context of watching television.
“Eyestrain can occur when the eyes are fixed on an object for a long period of time, there is poor lighting, or there is glare,” explains John Bullough, Ph.D., lighting scientist at the LRC and lead researcher on the television study. “One scenario believed to cause eyestrain is watching television in a dark room. In this case, visual discomfort is caused by the large difference in luminance between the television screen and the room’s dark background.”
Details of the study
Subjects participating in the LRC study watched one hour of action movie footage on a flat-screen television. Half of the participants first watched the movie footage with surrounding wall illumination. The group then took a break before watching another hour of footage without wall illumination. The remaining participants went through the same procedure, but in the reverse order.
Before and after viewing the footage, all subjects performed tasks in which they had to respond to visual cues by pressing a button. During the tasks, researchers monitored the participants’ electrical brain activity and noted changes between the start and end of each session. While the subjects viewed the television under each condition, the researchers monitored blink rates. They also questioned and observed the participants to evaluate the impact of surrounding illumination on subjective assessment of feelings.
In general, the surrounding illumination resulted in ratings of less visual discomfort, fatigue, and eyestrain, less frequent blink rates, and shorter durations of time between the presentation of a stimulus and brain wave responses.
“Each of these responses is consistent with the hypothesis that the surrounding illumination reduced visual fatigue and eyestrain,” says Yukio Akashi, Ph.D., senior research specialist at the LRC and member of the project team. “However, only subjective ratings of difficulty focusing and of sleepiness, and the reduction in the duration between the stimulus onset and an electrophysiological brain response showed statistically significant differences between the two conditions.”
Even though the effects were modest, they were measurable. The results are consistent with prior literature supporting the concept of limiting luminance ratios between a visual task and its surround, according to LRC researchers.
“This project was an opportunity to build a bridge between our subjective impressions about visual comfort and eyestrain, and physiological responses that can be measured in a consistent and repeatable way," says Mariana Figueiro, Ph.D., LRC program director. "These findings may also have implications for the workplace, as well as for display applications in aviation, security, and healthcare."
Philips Innovative Applications provided project funding, as well as an Ambilight flat-screen television that was used during the experiment.
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.
Materials provided by Lighting Research Center, Rensselaer Polytechnic Institute. Note: Content may be edited for style and length.
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