I have a 250w DE Pheonix 14k. Curious how can you tell by looking at it. Not sure on age of bulb. Does it get less blue, or burn coral? Any ideas are welcome..
It's hard to tell without a meter or without a reference. Seeing it everyday, you may never tell. Usually, they'll dim and the colors won't pop as much. I replace my DE's every 12 months just to be on the safe side (SE's at 9 months, PC/VHO's at 6 months). That may be a bit overkill, but I can always tell the difference and would rather be safe than sorry.
I agree with gflat. The phoenix bulbs are good at holding their overall par and I remember reading somewhere that they are about 80% efficient at 1 year and drop to about 70% efficiency at 2 years, but what I read did not speculate or give information about the color shift that takes place. I use phoenix bulbs and replace every 6-12 months.