I always figured that the reason the Normandy SR1 and the Alliance refitted SR2 were so dark was because it's supposed to be a stealth ship and the Alliance decided to remove any superfluous lighting to reduce the power costs.
Cause if the ship isn't wasting power on non-essentials, that means they don't have as big an energy signature to hide and so the heat sinks aren't being taxed as much, so they can remain hidden in stealth for longer periods of time.
We already have LEDs that can last 100,000 hours and perform optimally on minimal power, just imagine how much more efficient lighting technology will be in the future. I don't think their lighting draws enough power to affect the performance of the stealth drive in any way.