Some sources say that white light = R+O+Y+G+B+I+V while others = R + B + G
my question is do they divide the wavelength range (400-700nm) when they talk about RBG eg 400-500 = B 500-600 = G 600- 700 = R
and same for ROYGBIV but this time among 7 colours?
The only reason that RGB can make up white light is that our eyes can perceive those three colours. There is nothing *physically *special about red green and blue light except our biology.
White light is made up of a superposition of a large range of wavelengths, but we only have RGB cones so our eyes can be 'tricked' into seeing white light when in fact we are only seeing light of three wavelengths (as when all the pixels of the TV are active.) An alien with the ability to see more than these wavelengths would not view our screens as white when we do.
ROYGBIV comes from the colours of the rainbow as described by Isaac Newton and he named 7 colours for no scientifically valid reason but rather it was in keeping with tradition at the time. He could have chosen a different number of colours because there is no sharp dividing line between them.
