The Mirror Array is a simple mechanical device in Metroid Prime located in the Sunchamber. It is designed to produce artificial sunlight in order to keep the mutant plant, Flaahgra alive. Samus Aran is required to knock it offline by firing her weapons at the red orb on the reflector.
Metroid Prime and Metroid Fusion: Prima's Official Strategy Guide refers to them as "reflectors".
"Mirror Array used to focus sunlight onto creature. It looks like it can be tilted, possibly to take it offline."