One of the reasons light is so useful is that, although it can do some pretty complicated things, it operates according to fairly straightforward rules. That might be hard to believe when you stand between two mirrors that face each other almost perfectly, and you can see a reflection of yourself going off into infinity, but that’s just a simple rule being applied over and over again with each reflection. Tri-fold mirrors operate by those same simple rules.

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Originally published at eHow, SEP 2011