Morrison's Mailbag: Will leaving my HDTV on affect the picture?

CNET reader Ray asks:

Will leaving my TV powered on (but on black screen) for an extended period of time do any damage or affect the picture quality?

For reasons that made sense (but I left out for space), CNET reader Ray leaves his HDTV on 24 hours a day. The cable box it's attached to is "off," but like most DVRs it still outputs a signal (because it's not actually off).

So the TV is on, but creating a blank screen. Beyond the massive waste of power this is, the real question is if the TV itself will suffer.

The first thing to know is that all TVs dim over time. The phosphors in a plasma, the CCFL lamps in traditional LCDs, and even the LEDs in LED LCDs, all age over time. As they age they get less efficient, meaning that given the same amount of power, they produce less light. It's possible that you could drive them harder (like turning up the contrast control with plasmas, or turning up the backlight control with LCDs) to create the same amount of light, but there's a limited extent to which this is possible, either. After a while, you'll reach the maximum setting, and the TV will still get dimmer.

So in the long run, the a TV left on all the time will get dimmer, sooner, than if you only watched it 4 to 6 hours a day. Reducing the backlight control (many LCDs) or turning down the contrast (plasma) may extend the TV's life some, but only to a degree. Think of it like a candle; there's only so many hours it will burn.

With plasmas, displaying a blank, black image won't age the phosphors as much as a similar amount of time watching normal content. Here the candle analogy holds: a candle with a barely visible flame (the black screen) won't burn it down as fast as a bright, tall flame (normal content). The same isn't true with LCDs. Their backlights, either CCFLs or LEDs, create the same amount of light regardless of the image onscreen. So for them, blank screen or normal content, they'll age the same, unless you reduce the backlight.

An exception is with auto-dimming backlights, which I talk about in my article about contrast ratio. These automatically vary the intensity of the backlight depending what's onscreen. If your TV is so equipped, a blank/black screen will slow its aging if you have to leave it on.

Something else to be concerned about is image retention. If you leave a static image on any TV for extended periods, you run the risk of "burning" that image into the screen. It's more likely this will happen with a plasma, but it can happen with LCDs as well. Generally, if you just watch something else for a few hours, the "stuck" image will disappear.

Permanent burn in is much harder to achieve, but given the length of unsupervised time we're talking about here, it's possible. Ray says the screen is blank, so there no issue with his TV. But if you leave your TV on all day with an image, make sure the whole screen changes (don't forget about station logos).

For more info on this, check out Is plasma HDTV burn-in a problem? which discusses LCD image retention as well.

So to answer Ray's question, in the short term it's unlikely that leaving the TV on will result in noticeable picture quality issues. The long term, however, is going to be less long, as the TV is aging much faster than normal.

If you're curious about TV lifespan in general, check out "How long do TVs last?" and David Katzmaier's "Long-term plasma TV tests."

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