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Should I Put a Bias Light Behind My Flat Panel TV?

Al Griffin  |  Nov 6, 2014

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Q Is there any benefit to using a bias light behind a flat-panel HDTV? —Mike Hassold

A Yes, there is—the benefits of bias lighting are the same for flat-panel LCD and plasma TVs as they were for CRT TVs. Bias lighting is actually more of an issue for LCD models since these are capable of higher brightness than other display technologies. Watching movies in a dark room heightens picture contrast and can make colors appear richer. It also eliminates onscreen reflections from lamps and other sources of illumination. The downside? Eyestrain and viewing fatigue during extended movie viewing or gaming sessions.

Placing a bias light behind the TV helps to reduce the eyestrain that’s a side effect of dark or dim-room viewing. But you can’t use just any old lamp; it needs to have the same 6500K color temperature spec as a a properly calibrated video display.

If your flat-panel TV is installed on a stand, adding a bias light won’t be a problem. But wall-mounted flat-panel sets are a different story. Fortunately, you can purchase a bias light with a 6500K color temperature spec that’s thin enough to be installed even behind wall-mounted flat-panel TVs. The Ideal-lume Panelight ($95) was designed specifically for this purpose. The same company also sells the Ideal-lume Standard ($65) for non-wall-mounted LCD and plasma TVs.

If you really want to go crazy, follow the company’s recommendations and maximize the benefits of your bias light by also painting the back wall of your room a neutral gray tone. But for most people, simply sticking a light behind the screen will go a long way toward improving their home movie-viewing experience.

COMMENTS
rpali's picture
Submitted by rpali on November 6, 2014 - 9:32pm

First you must get a properly neutral light, but then you're going beyond the reasonable (crazy, right?) if you have neutral paint?

I'd suggest that if you don't do both, you may as well save yourself the money and do neither. After all, now neutral is that 6500K light going to look after reflecting off the slightly yellow wall behind the television? You may as well use an incandescent light and not pretend that the colour temperature matters to you.

Alan Brown's picture
Submitted by Alan Brown on November 20, 2014 - 7:50am

Incandescent lights are prominently yellow in spectrum. Using one to illuminate a yellow tinted wall would intensify the coloration. Not using anything will not solve the eye strain or fatigue issue. Individuals have differing sensitivity to eye strain.

The video industry standards organizations publish recommended practices for the average human viewer. International standards bodies have all consistently recommended using bias lighting in dark viewing conditions, including for newer displays that should fill a larger field of view (30 degrees) for an optimum HDTV viewing experience.

Wall color behind a video display should always be neutral white to gray. This is seldom understood properly by interior designers. Surrounding a picture with a color other than neutral will always skew the viewer's perception of the image on the screen. It works subtractively. Surround the image with blue and the viewer will perceive less blue in the picture.

Another benefit with bias lighting in dark viewing conditions is how it enhances perceived contrast in the image. With ambient light in the room, blacks on the screen will darken, but the lighter portions of the image remain the same. It's a human perceptual phenomenon commonly understood in imaging science circles. Ambient light must be kept at a reasonably low level and not allowed to introduce veiling haze or reflections on the screen.

Thomas J. Norton's picture
Submitted by Thomas J. Norton on November 7, 2014 - 11:23am
I understand the arguments for using a bias light, and they're good ones. But they ignore one important (to me anyway) factor. A movie, or a dramatic TV show, attempts to transport the viewer into its world, immersing you into the action. Granted, this is never perfect, and only comes close if the drama is up to it. But by turning off the lights, you remove extraneous distractions that can further reduce this immersion. No matter how dim the room lighting (or the bias light) is, it's simply another reminder that you're watching in a living, family, or media room surrounded by family and friends. The latter, by the way, are also less likely to offer distracting remarks or conversation starters as the ambient light in the room decreases!

Those are just some of the reasons why I prefer leaving the room lights off for serious viewing. The light from the screen will of course provide some illumination to the room unless you live in a black hole, but it's usually the best you can do.

The arguments for a bias light were more pertinent back in the day when a 32-inch screen was considered gigantic. But even with a 65-inch HDTV, if the set it turned up to a level that's comfortable in a fully lit room it may well be unpleasantly bright in a dark setting. That's even more the case with an LCD HDTV than with a plasma. If a plasma and an LCD are set for about the same subjective brightness on an average scene, the LCD will appear much brighter on, say, a brightly lit sky shot or snowscape. LCDs can simply pump out more peak brightness than a plasma. The solution is to decrease the set's overall brightness for viewing in a darkened room; that's why ISF-certified sets offer Day and Night calibration modes.

As a reviewer, however, I personally have another reason for viewing in a darkened room. It's the only way to critically judge the black level and shadow detail a set offers. Since the viewing room's brightness level will vary wildly from user to user, turning the lights off is also the only environment that at least comes close to a situation most readers can duplicate--depending on the reflectivity of their rooms.

Alan Brown's picture
Submitted by Alan Brown on November 20, 2014 - 8:22am

Among humans there is plenty of room for varying priorities, preferences, and practices in viewing motion pictures. Immersion is a powerful element in cinematic story telling. Unfortunately, screen brightness much greater than typical projection systems can cause fatigue and strain due to the repeated fluctuations in scene content throughout a program, even on very large displays. These fluctuations produce a strobing effect, or what a driver typically experiences at night on a highway with oncoming traffic.

The brightest projected images do not usually exceed 18 to 20 foot Lamberts. Calibrated video monitors/TVs are recommended to have a peak white of 30 to 35 foot Lamberts for dark room viewing with bias lighting. This recommendation has been maintained into the HD era by the ITU for evaluation of picture quality on high definition televisions.

MatthewWeflen's picture
Submitted by MatthewWeflen on November 8, 2014 - 9:44am

Buy, just looking at that image above makes my eyes hurt.

There's life beyond "Vivid," people!

Thomas J. Norton's picture
Submitted by Thomas J. Norton on November 20, 2014 - 10:33am
Fair enough, Alan. Individual tolerance for viewing 30 ft-L in a darkened room varies, and one must also take into account the tolerance of others viewing the set at the same time. But on an LCD set it's relatively easy to drop the brightness without causing serious disruptions to the picture by using the backlight control. While there's no such control on a plasma, as I've noted above an LCD set tends to look much brighter than a plasma on a peak brightness scene (even when both are set to be identical with a white window test pattern). It's on such scenes where eye fatigue is most likely on an LCD.

This may become a more significant controversy when and if high dynamic range, a feature now much discussed, becomes widely available on our program sources and HDTVs. Until then, by all means try watching movies both with and without a bias light (after making sure that the picture brightness is more suited to dim lighting than daylight!). Individual preferences and comfort levels will vary.

A bias light works best when there are no other objects or distractions in your line of sight to the television. The wall behind the set should be a neutral gray, with no hanging pictures, bookcases, windows, or other furniture immediately visible. This is the situation in most good professional monitoring rooms, but not in your typical domestic space!

An additional point: Just as your 2-channel stereo system may well sound better in the dark than in room lighting, your movie surround sound will as well!

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