Hey Al-
Awesome job on the article. It's nice to finally have some complete data tracking lamps from burn in to a solid year later...
You got me to dig and find my old thread from a year ago where I compared old Phoenix lamps to brand new ones and you mentined starting your study:
http://archive.reefcentral.com/forum...hreadid=787010
I'll measure mine this weekend since it's been another solid year, and I never did replace the other 2 bulbs (I'm getting ready for 400W Radiums), so they're over 6000 hours each. That might give you a little more data to play with. I didn't do any monthly readings, but hopefully I'll see something similar to your 6-9% difference in the extended use for my 2 older lamps.
I have visually compared the spectrum of newer lamps a few months back (over my frag tank) and the only spectral difference I can see with my eyes is the same difference I noticed in my thread from a year ago... where it looks like the actinic "pop" has faded (I assume that's the tiny little bump around 420nm fading away).
...and I still need to send those lamps to Sanjay...