lighting was given to me about 6 months ago. The MH
bulbs were already pretty old at the time but I used them for another 5 months (because bulbs are expensive!). The old bulbs were 10k. The new bulbs are 14k. Since getting the new bulbs, I've noticed a very significant increase in coralline algae growth on the glass.
So for those of you with bulbs getting old and wondering if it really makes a difference... it certainly did for me. Just thought I'd share my experience.