[Stereolithography](https://en.wikipedia.org/wiki/Stereolithography) produces parts by projecting ultraviolet light on the top of a vat of liquid photopolymer, causing it to harden. [CLIP](https://en.wikipedia.org/wiki/Continuous_Liquid_Interface_Production) produces parts by projecting ultraviolet light through the bottom of a vat of liquid photopolymer, causing it to harden. This seems like a minor difference, yet CLIP is reportedly much faster (I've seen numbers as high as 100x). Why is this?