What color temp are the bulbs? I've noticed that my plants under 5,000K bulbs have darker leaves than those under 6,500K, unless i was imagining things.lol I'm not positive, 'cause I didn't use 5,000K bulbs for very long, but, I swear that the leaves are a brighter greeen, now that they're under 6,500K. If I'm right, then a lower color temp would likely be even more noticeable.