His drain would be from almost any light source outside of the sun. The more concentrated the light the faster he would recharge. Think of the sun as the most diffused source of light, meaning he could try and collect it for hours and he might get enough to make an end game tooltip show up to explain he needed to drain it...He would drain things like flash bangs and spotlights, a florescent light heck even his excess light can be partially reabsorbed.
Is this acceptable?