Conversation so far:
what type of energy is used in a compound microscope
A compound microscope uses light energy because they have a light source at the bottom
When did the compound microscope first come out?
Compound microscopes first appeared in Europe around 1620.
How does the compound microscope compare to a simple microscope?
A compound microscope enables more advanced illumination setups compared to simple microscopes, such as phase contrast.

Question: what is special about the illumination setup
Self-contained rewrite: what is special about the phase contrast illumination setup