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Old 04/15/2007, 01:06 PM   #10
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seandanekind's Avatar
Join Date: Feb 2002
Location: Columbus, Ohio
Posts: 1,302
OK, new data:

The PAR readings are the highest I could get spending about 2-3 minutes per fixture searching for the max value while maintaining the same 7" distance as before. Lamps A and D are the 2 that I replaced 14 months ago

Lamp A + Clean Glass = 915 PPFD
(appx 3400 hours for 425 starts)

Lamp B + Salty Glass = 810 PPFD
(appx 6400 hours for 800 starts)

Lamp C + Salty Glass = 890 PPFD
(appx 6400 hours for 800 starts)

Lamp D + Clean Glass = 1015 PPFD
(appx 3400 hours for 425 starts)

Taking my original data from 14 months ago...

So here are the percentages of PAR level retained after 14 months (appx 3400 hours for 425 starts):
A 915/1350 = 68%
B 810/1100 = 74%
C 890/1250 = 71%
D 1015/1450 = 70%

So roughly, all of these lamps are giving about 70% of the output they gave 14 months ago.

Assuming from my earlier measurement that these lamps (+reflector+ballast) are averaging 1400 PAR brand new, the 2 older lamps have retained 57% and 63% of their original output after more than 2 years.

So I'm seeing a 30% drop from the original PAR level in the first year (actually 14 months), and about another 10% drop from the original level the second year. I'd say that's pretty close to what Al found...

It's hard for me to be sure on the 2nd year since I never really got the initial measurement when those lamps first went into service. You can work the stats to show a 15% or 20% drop in the 2nd year if you really play with the numbers.

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