dtree

Hi Tom - even at 10,000 hours those bulbs could be burning pretty bright. HID lamps will be noticeably dimmer, or they may flicker slightly when nearing the end of their lifespan. Blue bulbs and standard metal halide will give more compact growth, with the blue being slightly more compact I have found. There are new fluorescent lights (T5) on the market which have a red and blue bulb at specific frequencies for plant growth, red for flowering and blue for vegetative. They seem to produce excellent results with the added benefit of very little heat.
-dtree