UV filter is called ultraviolet filter, namely UltraViolet. It is usually colorless and transparent, but some of them will appear purple or purple-red when viewed from certain angles because of the anti-reflection film. 

Camera UV filter can protect the lens, avoid direct contact with the front glass of the lens and cause damage, absorb ultraviolet rays, remove fog, increase image clarity, and multi-layer coating process, which can promote color restoration balance.

 
Many people buy UV filter to protect the delicate lens, but in fact, this is just an auxiliary function. The main function of UV filter is to absorb ultraviolet rays with a wavelength below 400 nanometers, and it has no filtering effect on other visible/invisible light. The reason why it can filter ultraviolet rays is that the lens contains lead, so UV filter is heavier than other lenses of the same size and thickness.