More specifically, does spf sunscreen work by reflecting UV or absorbing it?
I always assumed it reflected UV waves away from the body to protect the skin underneath, but then I see those “UV camera” photos where the sunscreen shows up dark which I was taught (if I remember correctly) means the sunscreen is absorbing all the UV and therefore not showing up on the image (no light being bounced into the lens). If it is being absorbed, does it disparate the energy somehow to stop it from harming the skin cells underneath? This has been bugging me for quite some time. Please help.
In: Physics
I think it might help to understand what colors and how we see them when there is light on it.
Light from the sun basically has ALL the colors. When we see something of a certain color such as a red shirt, it actually mean that our eyes receive red light. But the shirt isn’t emitting light. So how come we see red? Simply because the dye used on the shirt ABSORB the other colors (usually turning them into heat). So that red shirt is red because all other colors are absorbed. Which also explain why shining a green light on a red shirt (like in a discotheque) lead to the shirt showing black: it has no red light to refract. It’s also why dark clothes usually keep you warmer, they absorb most color and turn them into heat.
Now, what are UV? Ultra Violet is a form of light. It just happens that our eyes are not capable of perceiving it. But they act pretty much like all other lights. Which mean, that with the proper dye, you can absorb it. That’s what sunscreen can be summarized as. A dye of an invisible color (basically, that doesn’t reflect any color our eye is capable of seeing) that absorb UV.
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