For exaple when you put a piece of red plastic in front of a flashlight how can the wavelengths just change?
In: Physics
A red piece of plastic is red because it reflects red light. The question is what happens to all the wavelengths of light that is not red. Depending on the plastic and the wavelength it can be absorbed or it could go straight through. So a material will end up being transparent to a completely different set of wavelength then it reflects. The only thing you can say about the light going through red plastic is that it have significantly less red in it then originally.
It should also be noted that humans have a relatively limited color vision. We can only see three different ranges of wavelengths and have to interpret the color of the light from this information. So for example a light composed of two different wavelengths may trigger the same cones as another light with a single wavelength. But these will behave differently when passing through different filters. Similarly cameras do not see the same ranges of wavelengths as humans and this is also perticularly noticable if you start filtering out single wavelengths.
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