• Question: How does light pain our eyes? Can light burn the surface of our eyes (sorry, quite a nasty question) how can light be dangerous?

    Asked by dizzyg12 to Susan, Simon on 19 Nov 2013.
    • Photo: Simon Langley-Evans

      Simon Langley-Evans answered on 19 Nov 2013:

      Not all of the cells in the eyes are supposed to pick up light. The lens of the eye focuses light onto those specific cells. If you go from an area of dim light to an area of brighter light it can make you feel pain because the pupil of the eye is open wide to let in light in dim conditions and doesn’t adapt quickly enough. Mostly you notice light as painful or unpleasant when you wake up first thing in the morning and your mum puts the light on to force you out of bed.

      Light doesn’t usually burn the surface of our eyes but looking into the sun (especially through a telescope or binoculars) or into a strong laser will irreversibly damage the cells at the back of the retina, causing blindness

    • Photo: Susan Skelton

      Susan Skelton answered on 20 Nov 2013:

      Nice to hear from you again, dizzy!

      This is a very important question, especially for scientists like me who use lasers in our work.

      Light can cause pain in our eyes if it is very bright. This happens when our light detectors are totally maxed-out and just cannot detect anymore light! This is what Simon described in his answer, however this is not a very dangerous situation because the eye has an in-built mechanism to protect you from this sort of light. If your room is suddenly flooded with light when your Mum opens your curtains, the pupil (the black bit in the middle of your eye, which lets the light in) gets smaller to reduce the amount of light that can enter your eye. If this is not enough, the pain causes us to automatically just close our eyelids!

      What is much more dangerous is the light that we cannot see!!! We humans can only see a small part of the light spectrum, from wavelengths of 400 nanometers (blue light) up to 700 nanometers (red light). Light with wavelengths shorter than 400 nanometres (ultraviolet), or longer than 700 nanometres (infrared) is invisible to us, but still very dangerous! Because we cannot see this light, our eye doesn’t respond by making the pupil smaller or by closing the eyelid.

      I use these types of invisible light in my experiments, so I have to be very careful that the light doesn’t go in my eye and damage it without my eyes and brain noticing.

      The type of damage to the eye depends on the wavelength (colour) of the light. Light that we can see can burn the retina at the back of they eye. Infrared light does not make it to the retina as it is absorbed by the cornea (the surface of the eye) which gets burned.

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