Screen size (diagonal size) and the dimensions of the TV are calculated based on the size of the premises, where there will be vehicles to be purchased, the distance from the viewer to the screen and its purpose.
The parameters of the diagonal expressed in inches ("), and usually indicates 2 digits – diagonal visible area of the image and the full size of the CRT or liquid crystal matrix. Some companies go to the tricks and point not visible, but full size, so when buying you should check both indicators.
All televisions usually belong to several groups. Most often it is 14", 20", 21", 25", 32" and 36" screens. Along with the growth of the diagonal increase and the size of the TV. So if you are planning to buy a flat screen TV from 25", then immediately calculate and place under the TV, even LCD TV has a depth of 60 cm To the same? safety standards between the housing and the wall or walls of the niche should be a gap to prevent overheating of equipment.
According to the same safety standards, but for health, you need to calculate diagonal size and at the recommended distance from the viewer's eye to the screen. If this is the standard TV 4:3 format, the distance should be not less than 3, but better 5 the diagonals of TV.
Think what place will be organized by watching TV, where there will be a TV, measure the distance and divide it by 5. The resulting figure will be the maximum diagonal of the TV. For example, a chair on which to sit a spectator, separated from television cabinets to 3 meters, it turns out that the optimal diagonal will be 60 cm or 24 inches.
Divide the distance in 3 is only in the case if you aim to purchase LCD TV with a scan of at least 100 Hz and 4:3 format. Such TVs at a relatively close distance a flickering screen which is the main negative factor affecting health, almost imperceptibly.
Radiation at such distances is not harmful, it can pose a hazard only in the immediate vicinity of the screen at a distance of a few centimeters. For LCD TV format 16:9 recommended distance is at least 2.5 diagonal screen.