Has anybody done a concrete study of how much PAR decreases with bulb age?

[cr500_af]

Just curious... I've tested a couple of 250w MH lamps and one Viper 150w. The 250s were completely unknown age; the Viper had a one year old Phoenix 14K in it. The PAR numbers were very poor on all of them (a different, also unknown age bulb got the 250 where it should be).

I am tempted to go ahead and buy a new bulb and put the Viper back in use, but if the PAR doesn't double, it will be money down the drain. I haven't found any PAR readings on the Vipers, so I'm hoping to get a general feel for how much PAR it would have lost in a year.

 

[ichthyoid]

Barry,

I read that some work has been done, but the controls were poorly implemented. From what I have found, PAR decreases at least as fast as lumens do. Sanjay studied this a little. I came across a study by a guy who was looking at his Phoenix 14k's and found about 40% drop in 1 year. He also found about 30% in the first 3-4 months! (IceCap ballast) Wow! So it seems to drop fast then slow after the first 3-4 months. Ushio has a 10K DE bulb that only loses 20% (max) lumens in 6000 hours. That's 2 years, if you burn the bulbs 8 hours per day. I'm thinking of using them supplemented with 420 and 450 actinic T-5's. I was all for the Phoenix 14K's until I saw the spectrum and aging data. The spectrum of the Phoenix is pretty flat except for a peak at 450.

Here's the Ushio link, lumen charts are about 2/3 of the way down:

http://www.ushio.com/products/petcare/aqualite.htm">http://www.ushio.com/products/petcare/aqualite.htm</a>

Notice the big difference between the 10K and 14K bulbs! It appears that the high the color temp, the faster the drop also.

 

[cr500_af]

Thank you. In particular, on the Viper, since I know the age of the bulb within one month... a PAR reading on her tank showed 300-ish at the surface (circulation pumps running), but dropped to below 100 at the sand (Oceanic 30g cube). I am torn over whether to replace this bulb and put the light back in use, or go another direction. I almost bought a 150w Radium but chickened out!

For the entertainment value: On my frag tank, Rob and I tried 3 "who knows how old" bulbs... a 20K, a 15K and a 10K (all name brands but I don't recall them). The 10K was the only one that made enough PAR to use (around 600 at the depth of the rack). The 15K and 20K made less than 150 at that depth (this was about halfway up in a 10" deep tank), all running on an Ice Cap ballast/Lumenarc combo.