The eye is sensitive to the rays of the visible spectrum, to be sure, but it is also sensitive to those that are invisible, and in particular to ultraviolet rays. Ultraviolet radiation (UVA, UVB, UVC) has a great many beneficial biological effects (photoprotective pigmentation, vitamin D synthesis) but it also presents a danger to the eye and the skin. Using a spectrophotometer we can measure the percentage of visible rays and UV rays that passes through a sample, and see whether the material blocks the rays or not, and if so, which type.
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