What 2 colours of the spectrum is invisable to the naked eye?
Infra red and Ultra Violet – they lie outside the range of human vision. There may be more colours, but we can not see them, so we have grouped all the reds below our range as Infra red, and all the violets above our range as Ultra Violet. The human eye is most sensitive to yellow, and when we get old, we loose the red and Violet colours as well, that’s why grannies dye their hair that silly blue rinse, it looks blond to them, and they prefer brown colours in the house decoration, as red blues get darker to them. We can see Ultra violet in very low light conditions, it makes our underwear sparrkle in night clubs – and infra red was discovered when electronics was tinkered with. If you use night vision, it is using the long waves of IR to illuminate an object.
