We get that question a lot in our electronic service department. First and foremost, nothing is wrong with your TV set. The real reason why you see bars on the left and right side of your new HDTV has to do with picture size.
Originally TV sets were round and it would have been difficult to show a wide screen format on them. The 4:3 format was adopted to fit the round screen of old TVs. That worked just fine for decades, until technology progressed. Along comes HDTV and in addition to greatly improving the picture, they decided to make it 16:9 widescreen as well to emulate the movie experience. Obviously, if you take a 4:3 SD picture and try to show it on a 16:9 widescreen, it will not fit. Enter pillar boxes, or vertical bars on the left and right of the screen. It may seem obnoxious to look at left and right bars when watching an older program on an HDTV, but it beats the alternative of having to stretch the entire image, making everything look awkward.
Why Gray Bars and Sometimes Black Bars?
If you are curious as to why sometimes the bars are black or gray, well, that’s up to the manufacturer. Gray bars reduce the aging difference between the SD picture and the pillar box areas of the screen. If the pillar box areas of the screen were left black, the phosphors would not age as fast in those areas as the picture area would. Using the gray pillar box areas will cause the phosphors to age roughly the same as the picture area.
So why sometimes are there black bars? The black bars are added by the broadcasters for the 16:9 sub-channels. Once a sub-channel is formatted for 16:9 HD material, they will not switch the format. They just merge the 4:3 SD video into the black 16:9 frame. They could switch formats between the SD format of 480p and the HD format of 720p or 1080i, but that will cause most TV to blink and stutter while they resync to the new format, so they don’t switch formats back and forth.