Your eyes have two different light receptors located on the back of the eyeball. These are the rods, which see black, white and grays can detect different intensities. The cones can detect color when the light strikes the cells that have a color-sensing chemical reaction that gets activated and sends a pulse to the brain. There are three cones: red, which can detect red wavelengths and some orange and yellow, green cones (which can also detect blue and yellow) are the most sensitive to light, and blue cones.

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So when white light hits your retina, all three cones are activated, and all three cones send signals to the brain, which puts these messages together to see white light.

In order to adapt to the dark, our eyes make a chemical called visual purple. This helps the rods to see and transmit what you see in situations where there is little light.

Your pupils also increase in diameter in the darkness. This allows for a slight increase in the amount of light entering your eye. This combination of visual purple and more light makes it possible for you to see in darker situations. We’ll talk more about this later when we look at The Eye.

Click here to go to next lesson on Light Absorption

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