• Question: Why can we only see visible light and not other electromagnetic waves through our eyes?

    Asked by anon-74226 on 29 Apr 2020.
    • Photo: Craig Leff

      Craig Leff answered on 29 Apr 2020:

      That’s how evolution has worked out for us — we only needed to see visible light and our eyes and brain filter out blue light so that light reflected from the sky doesn’t swamp everything. Our eyes are poor at picking out shades of blue compared to other colours, and is best at the yellow/green boundary. Night vision might be cool 🙂 but I’m not sure how the biology for that would work (really big eyes like an owl or a tarsier?) Butterflies and bees can see other wavelengths because they co-evolved with flowers, who have UV “landing strips” for them. Interestingly, we may have more capabilities which are masked — the painter Monet painted murkier colours when his eyes got bad, and after eye surgery he started painting odd colours — it has been suggested that when his eye’s lens was removed he could then perceive UV and other wavelengths. Interesting theory, but I’m not recommending running that experiment!

    • Photo: Paul Pitcher

      Paul Pitcher answered on 29 Apr 2020:

      Of course it’s well known that cats and dogs can see some amount of UV light. For whatever reason, our eyes aren’t sensitive to electromagnetic waves outside of a certain wavelength. I suppose this is because it’s not needed or not too advantageous to our survival or to our lives. I’m not sure of the biological detail of how the anatomy of our eyes differs to animals. So this is a great question but not necessarily one that has an answer. Why do we have five fingers, or two nostrils, there are certain things where the ‘why’ has no answer. Maybe there is a biologist who can answer to the anatomy?

    • Photo: Valentin Kokorin

      Valentin Kokorin answered on 29 Apr 2020:

      I think the reason we have evolved to see visible light, is due to our lifestyle being biased towards daytime. Our ancestors might have had an extended range, but it dropped off to better suit our behavioural trend.

      When it comes to either side of visible light, UV or IR – some other animals can sense IR and see UV.

      You also have to consider that humans live for quite a long time, so possibly seeing in UV would increase risk of damaging the rest of the eye mechanism.

    • Photo: Kimberly Bartlett

      Kimberly Bartlett answered on 29 Apr 2020: last edited 29 Apr 2020 3:12 pm

      Our eyes have evolved to have special cells inside them that are designed to react to certain wavelengths of light and convert those wavelengths in to something we can see. These are rods and cone cells. The rods help us see in the dark but only work in black and white, and the cones let us see red, green and blue colours but only in good light. The eye does sense wavelengths outside of the visible spectrum, like ultraviolet and infra red but the brain does not allow these signals to be converted to visible signals. The blue and ultraviolet wavelengths are sensed by a special cell called a photosensitive ganglion which sets and maintains your body clock depending on how much of these wavelengths enter your eye.

      The eye is a great sensor and the brain is great at decoding these signals but it takes so much energy and power to do it that there is only so much it can see before it overloads and shuts down for a rest. Try looking along a landscape from left to right really fast (much easier in a car or on a train); the pictures you see will be jerky and you may even have bits that are missing. This is called a saccade. It is what happens when your brain tries to take in a lot of information at once. It will take little snapshots of what you see and then imagine the rest. I you have ever thought you have seen something, then looked again it was gone, it is usually the result of one of these imaginary in fills in the saccade.

      This is the most likely, evolutionary reason why we can’t see more wavelengths, the brain would not be able to cope with the amount of energy and information needed to do it, and there hasn’t been any real evolutionary advantage to being able to see xrays and other wavelengths in order to survive.

    • Photo: Jean-Luc Bulber

      Jean-Luc Bulber answered on 30 Apr 2020:

      That is to do with neuro-science. Not all humans even see the same level of detail. The typical example is colourblind people, of which there are also different types.

      There is actually an android app that allows you to simulate chromatic vision deficiency:
      Chromatic Vision Simulator

      The app is not necessarily accurate, but will give you an insight (no pun intended) of what it’s like to be visually impaired.

      While colourblindness used to be a significant disability for engineers (think about the electrician who works with coloured cables all day long), there are now tools to overcome this, like special glasses that people can wear. To make sure we integrate everyone, we also try not to rely only on colour coding, but use other identification methods (text, symbols) to avoid mistakes that could be linked to this type of deficiency.

    • Photo: Simon Porter

      Simon Porter answered on 30 Apr 2020:

      As posted in a number of other responses, the short answer is #becausebiology.
      Basically, it is all down to the wavelength of light and the effect that wavelength has when it interacts with the receptors in our eyes. As per other answers regarding wavelength bands just outside the visible range (Ultraviolet (UV) and Infra-Red (IR)) this is largely down to signal processing in the brain, but there are a huge range of other wavelengths of electromagnetic waves that we cannot see for different reasons.

      I’ll try to use an analogy to explain in a different way to the other answers.
      If you imagine a ship on the sea, the smaller the ship the more it ‘feels’ waves of all sizes – you feel small waves, and really big waves have the potential to overwhelm the ship. Similarly, a much larger ship will not notice small waves, but will ‘see’ big waves.
      This is the same as your eyes, if you imagine that your eyes need to notice a particular amount of wave to register, their size determines which waves it can see and which waves bypass it completely. That is why you cannot, for example, see radio waves – they are extremely long wavelengths and completely bypass our eyes. It is also one reason why you cannot see really short wavelengths like x-rays and gamma rays – they are too small for our eyes to notice.

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