Intensity of the harmful radiations coming out of TV screen is strong near it and gradually falls In simple terms, the eye consists of a cornea (in the front), eye lens (in the middle) and retina (at the back). The space between the cornea and the eye lens is filled with an aqueous humour and that between the lens and retina is filled with a vitreous humour. Ciliary muscles hold the eye lens in its place and also change the shape (curvature) of the lens (to adjust the focus on objects) along with the help of the fluids.
If one sits too close to the television or cinema screen, the eye Lens has to do more frequent focusing for viewing. Light rays from a near portion of the picture diverge and so the lens is curved more to focus on them. Simultaneously, the lens has to collect the light (coming more parallel) from more distant parts of the picture. This causes strain on the eye, and if practiced for long, can permanently damage the eye.
In addition, for optimum resolution of the picture and to reduce the level of radiation from the TV screen, we are advised to sit at a distance while watching the programmers.
In fact, the limit of resolution of the human eye is 1 mm at a distance of about 3 m. If one watches a TV sitting close to it one can see the picture elements (grains) which make up the picture. To see a clear sharp picture without eye strain, one must sit at an optimum distance so that the individual grains merge to form a complete picture.
In a typical case, the main field of vision of the eye is defined by the vertical and horizontal viewing of 30-40 degrees; beyond which the vision is poor. Therefore, for comfortable viewing, a viewing angle of 10-15 degrees at the eye is optimum.
The width-to-weight ratio of the TV screen is kept as 4:3 because of the binocular vision due to the pair of eyes in the horizontal plane and the range of movement of both the eyeballs being less restricted in the horizontal plane as compared to that in the vertical plane. Hence, the best viewing distance for watching TV is 4-8 times the height of the screen (for a visual angle of about 10 degrees). For 51-cm TV, the minimum viewing distance should be 2.5 m. this minimum distance reduces eye fatigue by avoiding rapid movement of the eyeballs.
Also the light that falls on the eyeball comes directly out of the TV screen. Hence the with the distance from the screen.
So, to reduce exposure to these radiations, it is better to sit a bit far away. (In a theatre, the light falling on the eye is actually those reflected by the wall/screen and so the harmful effects are less.)
To reduce the strain on the eye, there must be some light in the hall. And this should be placed preferably above or on the sides of the TV to avoid any glare from the screen.
