Within the human eye there are photoreceptors called rods and cones. When we look further into the cone we can distinguish that there are three different types of cones which best absorb different colours depending on the opsin molecule. The blue sensitive pigment can absorb at a maximum of 420 nanometres, the red sensitive pigment at a maximum of 530 nanometres and the green sensitive pigment at a maximum of 560 nanometres. These cones are responsible for all the colours of the electromagnetic spectrum that we see.

Figure 12.1 effectively represents the 3 different colour sensitive cones and at which wavelength their maximum absorption occurs.
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