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Posted by Casey (166.102.174.135) on November 13, 2002 at 15:26:06:
In Reply to: Projection TVs: Is the radiation from them less than for regular TVs? posted by John Williams on December 25, 2001 at 15:47:31:
: Does anyone have any information on whether there is less radiation from (for example) a 43" prjojection TV system than a regular CRT-TV screen?. Just wondering.
: Thanks for any responses.
: John
John,
There is no radiation from a projector set. All of the ones I have seen 'project' visible light onto the front 'or rear' of a screen. It's just light.
Regarding 'regular' televisions it's a totally different story. First of all color sets are worse than black and white. There have been steps made to improve this but it can't be eliminated.
It is caused primarily from a high voltage cathode (the viewing screen) accelerating electrons from the anode. When the electrons hit the screen, which illuminates the phosphor and makes the image you watch, x-rays are produced at the point of the impact and 'shoot' out of the front of the set.
Hold your arm (hairy side) up to a tv screen and you can feel your hair react to the high voltage (anywhere from 30-70 Kv (thousands of volts) or more.
For children in particular it is very important to sit back away from the TV. Since the x-rays follow the 'inverse-square law' every time you double the distance the radiation falls off ny a factor of four (ie 2 sqaured = 4).
Regular NTSC (Not HD) televisions are designed with a certain viewing distance in mind. It is this that should dictate the size of tv you buy.
The rule is viewing distance = 2.5 x diagonal size of the tv. Again as an example, a 19" tv is designed for optimum viewing at 2.5 x 19" or 47". When buying a tv you should determine your viewing distance first, divide by 2.5 and then go get a tv that is within an inch or so of that value.
X-Rays are dangerous because the are what is referred to as 'ionizing' radiation. This means they have enough energy to knock electrons out of their normal orbits and ionize the molecule(s). This is very bad for eyes, brains and all other organs.
I hope this helps and if I missed something (I'm a bit rusty) someone please add there two cents worth.