• Question: Why does the light from the sun hurt your eyes when you look into it??

    Asked by bethan08 to Mark, Matthew, Mike, Paul, Sabina on 7 Mar 2014.
    • Photo: Matthew Malek

      Matthew Malek answered on 7 Mar 2014:

      Let me start by saying that it is very dangerous to look directly at the sun without taking proper precautions (like building a pinhole camera or, if you have more money to spend, buying a telescope with a hydrogen-alpha filter — those are REALLY awesome!).

      The light from the sun is quite intense, and the lens of your eye focuses that intensity right on your retina. This intense light can burn out your retina leading to partial blindness… but you won’t feel any pain as it happens. That’s because there are no pain receptors on the retina.

      The pain you feel when the sunlight is very bright comes from a different source. Light enters your eye through the pupils, and the size of the pupil is not fixed. Muscles in your eye can contract the pupil, letting in less light when it is bright out… or expand (“dilate”) the pupil to let in more light when it is dark. That’s where your night vision comes from — the pupil gets larger so more light can enter. (Since I do amateur astronomy, I have a strong interest in night vision!)

      You may notice that it takes time to get your full night vision when you enter a dark place. That’s because the muscles in the eye work slowly. When you go into bright sunlight, the eye muscles try to protect your eye by contracting the pupil quickly. It is this quick action by those muscles — not any reaction from the eye itself — that causes you to feel pain in very bright sunlight.

      Thanks for the question! It’s way outside my usual field of research, but I hope this helped! 😀

    • Photo: Sabina Hatch

      Sabina Hatch answered on 7 Mar 2014:

      Well I learnt something new too! Thanks for the answer Matthew!

    • Photo: Mark Jackson

      Mark Jackson answered on 7 Mar 2014:

      I’m assuming that if you could see the computer screen well enough to type the question, you haven’t done this. Whew, that’s a relief.

      Like all good questions in science, this one can be answered in Star Trek. There is an episode called Operation: Annihilate! in which Spock has been attacked by aliens resembling flying vomit-pancakes. The good news is that Kirk discovers intense light can kill the aliens. The bad news is that this also makes Spock go blind. Fortunately, Spock remembers that Vulcans have a second, inner eyelid to protect against the bright Vulcan sun, so the blindness was only temporary.

      Why would Humans not fare so well, you ask? We see because light travels through our eyeball to hit the back surface, the retina. The retina has evolved to only process the amount of light expected on a day-to-day basis. Excessive light entering your eye is more energy than your retina can handle, and it will – very literally – burn off. Your eyes hurting while staring at the sun is your body’s way of telling you this is a bad idea.

      So: unless you are a Vulcan, don’t stare into the sun.

    • Photo: Paul Coxon

      Paul Coxon answered on 17 Mar 2014:

      It’s very very intense, and not only does the sun’s light contain the white light of the rainbow spectrum, it also contains UV light causes damage to the body’s cells – especially the eyes and skin.

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