The colored lights(led or similar things) irradiate a narrower range according to its own emission spectrum. In that case,whatever the color of light, why does the light appears white in the center of all of them ?

Eg a green led produces some light that is detected by red and blue photodetectors. Since the centre is much brighter than the sides, all three colours get saturated and White is recorded. 

14 minutes ago, Bender said:

Eg a green led produces some light that is detected by red and blue photodetectors. Since the centre is much brighter than the sides, all three colours get saturated and White is recorded. 

Is this valid for the other monochromatic light source like red,blue,purple ect.. ?

Yes.

For purple and yellow, they are always triggering different photoreceptors, even at lower brightness. 

Even if you have a very very narrow band of emission- eg from a laser- it will look white  if it's bright enough- because the sensors are not narrow band.

 

 

Edited April 6, 20187 yr by John Cuthber

A lot of cameras display white when they are saturated. I assume that's what's going on in the pictures.