• Question: Why do we not see other things on the light spectrum?

    Asked by to Anna, Elaine, Fiona, Kevin, Darren on 17 Jun 2014. This question was also asked by .
    • Photo: Zhiming Darren Tan

      Zhiming Darren Tan answered on 17 Jun 2014:

      Our eyes are light detectors, sensitive to a certain range of the spectrum. Different eyes have different ranges, especially if the eyes belong to members of different species.

    • Photo: Kevin O'Dell

      Kevin O'Dell answered on 17 Jun 2014:

      Different animals have evolved to see in different wavelengths of light. I would imagine it is difficult or impossible for an eye to evolve that can see all wavelengths equally well (though I’d be happy to be corrected on this).

      I always find the easiest way to think about things like this is to use real-life examples. A few years ago we were interested in finding out what our fruit-flies got up to in the dark. Clearly you can’t film them in the dark because it’s dark, and they don’t really generate heat, so you can’t film using a heat-sensitive camera. But you can exploit the fact that they have red-pigmented eyes which means they cannot see in red light. So we simply put them in a room lit by red light. We can see them, but they can’t see us (or anything else for that matter).

      All very interesting except that in the dark (red light) fruit flies (surprise surprise) don’t actually do anything at all.

    • Photo: Elaine Cloutman-Green

      Elaine Cloutman-Green answered on 19 Jun 2014:

      What a fine question. Let me see if I can answer it. So, there are two reasons. The first is that the eye is only transparent to certain frequencies of light and so light outside of the visual range would tend to be absorbed before it got to the cornea which is the bit that actually detects light. The second is that we only have two types of light receptors, rods and cones. For very much longer wavelengths like radio, we would need a different sort of structure as the wavelength would be much bigger than a rod or a cone. For shorter wavelengths like ultraviolet, we would need smaller receptors that could survive the much higher energies of short wavelength electromagnetic radiation. Some sorts of really short radiation pass right through the sort of eyes that we have. The human eye is a pretty good compromise since an eye could not be good at very long wavelengths and very short ones

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