If you're wearing eyeglasses, and you lay out in the sun with your eyes clo!
Question: If you're wearing eyeglasses, and you lay out in the sun with your eyes closed...?
The reason I ask is that, on an episode the tv show Survivor, a pair of eyeglasses were used to start a fire with the sun's rays. So if the sun's rays (when shone through eyeglasses) can start a fire, could they also lightly burn skin or cause skin damage?
Answers:
When light passes through a convex lens, and it is held the proper distance away from the surface, it concentrates the light into a small area and can create enough heat to start a fire.The kind of lenses they use for correction of nearsightedness are concave lenses, so they will not focus the light to a spot, on the contrary, they disperse it so, no worry of burns regardless of strength of the glasses. Glasses for farsightedness or reading glasses have convex lenses which might possibly be used to start a fire. Even if a person fell asleep while wearing them, it probably wouldn't make the sunburn worse around their eyes because the skin is not close enough to the actual focal point of the lens. I suppose, possibly, if somebody was wearing glasses with such insanely strong convex lenses where the focal length was on the order half an inch, (the approxamite distance between the back of the lens and their eyelid) they might burn their eye lids, but I doubt anybody has ever needed a prescription that strong!
They probably focused it onto a point to start a fire (i did it with a magnifying glass) and i've tried burning ants with my pair of glasses but they never work. The glasses are probably close enough to your eyes that they won't do any damage but it will warm up your eyes a bit.
i wear glasses myself and i burn ants with a magnifying glass once and a while XD