The notion that watching TV in a dark room is bad for your eyes or, at least, causes eyestrain has been around for a long time. The problem is said to result from the contrast in light between the brightly lit TV screen and its darkened surroundings. The "harm" in this case was thought to be eyestrain, not any long-lasting damage to the eyes.
To find out whether or not eyestrain results from watching television in a darkened room, researchers from the Lighting Research Center (LRC), part of Rensselaer Polytechnic Institute, asked some volunteers to watch an hour of an action movie on a flat-screen TV. Half of the volunteers viewed the movie in a room where the walls surrounding the television were illuminated. They then took a break and later watched another hour of movie footage without wall illumination. Another group of participants did the same thing, but in reverse order – first in the dark environment and then in the illuminated one.
Before and after watching the movie footage, all of the participants were asked to respond to visual cues by pressing a button, an exercise that allowed the researchers to monitor the participants’ electrical brain activity and note any changes that occurred between the beginning and end of each session. And while the participants were watching the movie, the researchers monitored the rate at which they blinked their eyes. They also asked the participants to assess how the surrounding level of light affected them.
The result of all this testing and observation was that there was less eyestrain, discomfort and visual fatigue when the volunteers watched the movie against a lighted wall. But the only statistically significant differences were due to trouble focusing, sleepiness, and the time lapse between the onset of the visual cues test and electrophysiological brain responses. All told, the results could be interpreted as mildly critical of watching television in a dark room, but no real harm was found.
You might be interested to know that another persistent notion – that sitting too close to the television will hurt children’s eyes – is also not true. However, habitually sitting close to the TV may indicate that kids can’t see the screen clearly if they sit farther away, possibly suggesting a need for glasses.
Another myth holds that reading in dim light can hurt your eyes. That’s not true either, but reading in dim light can cause eyestrain or give you a headache. It is best to read with light shining directly onto the page.
Andrew Weil, M.D.
Lighting Research Center, Rensselaer Polytechnic Institute. "New Study Tests The Effects Of Watching TV In A Dark Room." ScienceDaily. 25 April 2006. http://www.sciencedaily.com/releases/2006/04/060425015643.htm, accessed July 3, 2014