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General Science => Question of the Week => Topic started by: thedoc on 15/10/2009 11:37:23

Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: thedoc on 15/10/2009 11:37:23
When I was younger I was told not to sit too close to the TV. Is it an urban myth that it's dangerous to sit too close? Or does the TV emit radiation? Does this still apply to modern televisions?
Asked by Claudia, Argentina

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Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: thedoc on 15/10/2009 11:37:23
We put this question to Andy Karam, adjunct professor at the Rochester Institute of Technology...

Andy -  Televisions really do give off radiation.  But having said that, it’s only a little bit of radiation and it’s not that dangerous.  What happens is that anything with a cathode ray tube, a tube where you shoot high-energy electrons at some sort of screen, when those electrons hit the screen, they give off very low energy x-ray radiation.  This is the same way that x-rays are produced in regular x-ray tubes.  So, if you're sitting close to a cathode ray tube, whether a computer monitor, a television screen, a radar set or anything else with that type of technology, you're going to be getting low doses of x-ray radiation.

[img float=left]/forum/copies/RTEmagicC_800px-1950__s_television_01.jpg.jpg[/img]Now having said that, I’ve got to emphasize, they're low doses of radiation.  It’s not enough to be dangerous and in fact, if you watch your television for several hours a day all year, you're getting less radiation than you would from a single medical x-ray and less radiation than you get from the radioactivity that’s just naturally within your body.  So, it’s something that we can measure, but it’s not something that’s harmful.

LCD and plasma screens don't give off any radiation at all.  They don't use high-energy electrons.  It’s a different type of technology.  I could not say that they're safer because I don't consider the radiation from cathode ray tubes to be a risk, but I can say that they give off less radiation.  As far as sitting too close to the television goes, the further back you are, the lower the radiation dose will be.  But having said that, I don't consider the radiation dose even at a distance of just one metre to be dangerous.

Title: Re: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: Bored chemist on 06/10/2009 18:50:19
If you sit too close you block the grown-up's view.
They can't sit so close because (generally) children have a better abillity to focus than adults.
Title: Re: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: Shibs on 06/10/2009 21:19:15
TV sets presumably have to conform to industrial standards nowadays, that they emit minimal radiation.

(Radiation is simply energy; it can be reflected, absorbed, or emitted.)


Whether a TV set is bad for your eyes is a different matter. Your eye muscles are put under strain to focus images through the lens. If you are looking at something a short distance from you, they have to work harder.

However, this doesn't cause long-term damage as such, as far a I know though (for most people.)
 [:)]
Title: Re: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: that mad man on 06/10/2009 23:46:45
I was told the same thing also but that was in the 1960's.

The early TV's had 405 lines and had a noticeable flicker to them. They also looked out of focus close up(from what I can remember). I don't think the public in those days knew much about TV radiation so I doubt that was why. IIRC The older CRT TV's emitted radiation but the forward radiation towards you is very low and not harmful.

Most modern TV's now have LCD screens with higher resolutions, mainly flicker free and emit no radiation. Its amazing how quickly they've gone from being a heavy square box to a large wall-mounted set. 
Title: Re: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: JnA on 07/10/2009 00:23:29
Urban Myth.. possibly stemming from a *little* truth. I agree with the mad man (never thought I'd be uttering those words again - sheesh!) it's less to prevent eyes damage and more eye strain.

Before 1968 some sets emitted excessive X-rays... so I guess a blanket warning was given and it stuck.. like the perceived warnings of the microwave and eating lead...  (wait that last one might be real)
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: chris on 07/10/2009 22:48:57
I always thought that CRTs emitted x-rays (albeit at low intensity) and this was the reason not to sit too close, so as to reduce the dose. But then again, unless they are coming off at very wide angles, the distance from the TV wouldn't make an enormous different to your dose would it, air not posing much of a barrier to an x-ray...
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: Shibs on 08/10/2009 10:19:04

It is not so much the angles at which these X-rays come off from a cathode ray tube that it is the issue.

From the fount of all knowledge, apart from TNS

CRTs can emit a small amount of X-ray radiation as a result of the electron beam's bombardment of the shadow mask/aperture grille and phosphors. The amount of radiation escaping the front of the monitor is widely considered unharmful.

The Food and Drug Administration regulations in 21 C.F.R. 1020.10 are used to strictly limit, for instance, television receivers to 0.5 milliroentgens per hour (mR/h) (0.13 µC/(kg·h) or 36 pA/kg) at a distance of 5 cm from any external surface; since 2007, most CRTs have emissions that fall well below this limit

Wikipedia.
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: Bored chemist on 08/10/2009 18:41:29
"TV's now have LCD screens ... and emit no radiation. "
Dark in here, isn't it.
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: Kupac on 10/10/2009 02:20:51
I don't know about X-rays, but there is another good reason why you should not spend a long time staring at anything from a short distance, especially as a kid. This has something to do with the development of the eyeballs and short sightedness. A child's eyes are smaller than an adult's, therefore they have to grow as one reaches adulthood. During this growth period, it is important to keep an appropriate shape and size, so that the picture projected onto the retina by lens is sharp. The exact mechanism is still unclear, but it appears, that it has something to do with the relaxed state of the lens. When you look in the distance (infinity) your lens is relaxed. If you need to  "focus" to look in the distance, it tells your body: "Your eyeballs are too small". So there is a growth response to distance the retina a bit farther away from the lens. This mechanism must have served really well in our evolutionary past, because humans looked in the distance quite often. But in the age of book printing, TV and the Internet it is not working that well at all. During growth we are staring at a monitor, and therefore our eyes are getting a lot of growth signals. So if you keep a distance from the TV it may help to prevent short sightedness. Or at least helps to have a less severe one.

Here is some reference, I hope I didn't misunderstand it completely :)
http://www.annals.edu.sg/pdf200401/V33N1p16.pdf
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: chris on 10/10/2009 10:08:57
Quote from: Bored chemist on 08/10/2009 18:41:29
"TV's now have LCD screens ... and emit no radiation. "
Dark in here, isn't it.

I don't agree. Every TV in my house is still CRT-based. There will be a long legacy of the old TV days before these old units are all replaced.

Chris
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: Bored chemist on 10/10/2009 18:11:31
Quote from: chris on 10/10/2009 10:08:57
Quote from: Bored chemist on 08/10/2009 18:41:29
"TV's now have LCD screens ... and emit no radiation. "
Dark in here, isn't it.

I don't agree. Every TV in my house is still CRT-based. There will be a long legacy of the old TV days before these old units are all replaced.

Chris
Just exactly how much use is an TV screen if it doesn't emit light?
Light is a form of radiation.
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: that mad man on 10/10/2009 21:51:08
Quote from: chris on 10/10/2009 10:08:57

I don't agree. Every TV in my house is still CRT-based. There will be a long legacy of the old TV days before these old units are all replaced.

Chris

It may be quicker than you think if they are old units. The analogue TV signal will be switched off in July 2011 so unless they are all digital receivers or you have separate digital box receiver/adaptors they wont receive a signal.
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: JP on 11/10/2009 05:37:37
Quote from: chris on 07/10/2009 22:48:57
I always thought that CRTs emitted x-rays (albeit at low intensity) and this was the reason not to sit too close, so as to reduce the dose. But then again, unless they are coming off at very wide angles, the distance from the TV wouldn't make an enormous different to your dose would it, air not posing much of a barrier to an x-ray...

Radiation intensity follows a 1/r2 law, so that if you double the distance to the TV, the radiation decreases fourfold.
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: RWeb on 13/10/2009 04:11:35
My father has a projector home theatre downstairs and apparently there's a rule of thumb that in a theatre viewing that the optimum distance is three times the height of the screen - meaning you have to be sitting 3x the heigh of the screen away for the optimum distance. This rule is used to determine where the seating and the speakers should go thereafer.

I wonder if this rule would apply to the TV world?
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: thedoc on 13/10/2009 19:41:36
Did we mention your answer on air?  Listen to the answer to this question on our podcast to find out... (http://www.thenakedscientists.com/HTML/podcasts/show/2009.10.11/)
Title: None
Post by: uzor on 15/10/2009 16:15:14
it is true it aint to dangerous to sit near the television because i remember when my i was having an experiment with my guinea rat is eyes where still intact and the t.v was near it
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: Jonathan Madriaga on 10/11/2009 05:16:45
Many people are led to believe that sitting close to a tv will damage your eyes in the long-term. I believe that was back in the day, where emissions were not properly regulated. Nowadays, tvs are optimized for human safety. As a general rule of thumb, people shouldn't sit close to the tv because it causes eye strain, just like sitting in front of a computer. Suggestions if you cannot see the picture, would be to get prescription glasses, or visit a Optometrist.
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: Gall on 15/02/2010 19:36:16
my grandmother often said that.. we should listen more often elderly people [:I]
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: geo driver on 16/02/2010 04:07:18
if you sit back then you can see the whole tv with out moving your eyes, and as BC said it blocks the tv for your parents, i try telling my daughter teat but does she listen when  her favorite cartoon comes on
Title: QotW - 09.10.11 - Why should we sit far from the TV?
Post by: maclhen on 04/04/2010 18:50:53
why should we sit far from tv?
because to avoid the ambiguity of our eyes...when we are too close it can damage  our eyes...We should beware because we are important to maintain our healthy eyes...









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Title: None
Post by: Martin on 17/11/2015 21:22:16
And what if you are visually impaired and have to sit closer, like 30-50cm from TV? Won't the radiation affect you more than the safe levels permit?