Effects of too much light or old bulbs?

[Madmak]

Just curious as I have a couple used 6' fixtures above my tank and want to be sure I recognize a problem early.

My 12 bulb T5 light has all new bulbs. My 3X150W (20K) Halide plus 4X96W PC (Actinic) light has used bulbs.

My controller ramps them up to a high noon effect and back down (by number of bulbs, not percentage). I thought my T5 fixture wasn't bright enough so added the Halide/PC fixture later.

Back to the question, what are the effects of too much light or old bulbs? I have no experience with this...