5. The eye and TV screens 

(from a physics point of view)

The eye and the brain work together when see light from objects viewed around us.

Different rods and cone cells at the back of the eye in the retina can detect red, green and blue light photons.

All these visible light photons have sufficient energy to trigger a tiny electrical impulse that goes to the brain from photosensitive protein molecules.

When all three types of cell (RGB cones) are triggered we see white, but each type of cone detects mainly red, green or blue photons.

Combinations of the cell responses create signals to the brain which it interprets into all the colours of the visible we see - violet, indigo, blue, green, yellow, orange and lots of shades in between!

and, things are even more complicated than that.

e.g. yellow light is detected by both red and green cones, so you don't really see a pure yellow colour.

For more on the structure and function of the eye (school biology notes)

Infrared photons do not have enough energy to trigger a response from the retinal cone cells, so we don't visually detect infrared EM radiation.

Ultraviolet photons have far more energy than visible light photons and can cause damage from chemical changes in the retinal cells.

Colour television uses the properties of primary colours. In a TV (and computer) screen there are three electron guns that hit a sort of paint called a phosphor.

When hit by electrons the phosphors glow either red, green or blue.

The screen consists of thousands of pixels each containing a set of the three phosphors.

By making these three phosphors glow at different intensities (brightness) they create the illusion of all the colours you experience when viewing the screen.

Digital cameras and colour printing also work on the basis of the three primary colours.