I just spoke with an experienced fish store owner, and he agreed both direct and ambient light would have a huge impact on the growth of algae.
He also said it's common when live rock is "smooshed" into the sand bed that it creates dead pockets for cyanobacteria to thrive. he suggested placing the rocks into the aquarium directly on the glass and just gently maneuver the sand around the rock. he said the rock might not be as stable on the glass versus the sand, but it's a pro vs. con type of thing.
he also mentioned a UV
sterilizer (which we don't have) will kill some algae spores... but perhaps that's just salesman talk.
in any event, what is the thought about live rock being placed directly on the glass and the sand gently moved next to the rock versus the sand first... then rock "smooshed" on top?