Why can humans see ultraviolet or infrared energy?
There are a few reasons for the range of wavelengths that we can see. One is that much of the interesting interactions between energy and objects happen in those wavelengths, so there is a lot of information for us to see there. There are also more “practical” reasons. UV energy is often damaging to biological tissue, so it would be potentially dangerous for our visual systems to absorb that energy. Some insect respond to UV energy, but they don’t live nearly as long as us, so maybe the potential damage is not so much an issue for them. At the other end of the spectrum it becomes difficult for biological photoreceptors to respond reliably. Basically, because of the temperature of our bodies, receptors that could respond to IR would also be very noisy (IR cameras are often cooled for this reason) and it would be difficult for us to differentiate noise produced by our visual system from objects out there in the world.
