How can a piece of colored plastic change the wavelength of light?

Question

For exaple when you put a piece of red plastic in front of a flashlight how can the wavelengths just change?

In: Physics

Answer 1

They don’t – coloured plastic basically acts like a filter. Most light we interact with isnt one wavelength but a combination of various wavelengths, with white light being a relatively even distribution across the visible spectrum. If you shine white light through red cellophane all the non-red wavelengths are absorbed while the red passes unhindered, and you now have a red light.