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Re: T-8 lamp and ballast questions (fwd)

>Your experience let me puzzled. How do you relate your observations with
>the manufacturer's data ? I have a lumen maintenance curve that compares 
>T-5, T-8 and T-12 tubes (from a Philips publication). The T-8 curve shows
>a drop from 100% to 90% at 5,000 hours. From then on the lumen level falls
>off just a little, to 88% at 20,000 hours, their average life. That's
>about 4.5 years @ 12h/day. T-12s on the othe hand will fall to about 75% 
>initial lumens @ 2,000 hours, and continue falling steadily to below 50%.
>They have an average life of 7,500 hours typically, or about 1.5 years.

My T8's were GE SP50's, running in a relativly open fixture (a suspended
reflector). According to grainger, they lose about 10% of their output over
their rated 20000 hour life. I have had problems with darkened ends of the
tubes which resulted in uneven illumination and a few premature failures. I
have usually found that with about 1-2 years of use I would start to see
some darkened ends. The darkened ends resulted in lower light levels in the
ends of the tank, and the ends are harder to light well in my tank.

>On the other hand you seem to imply that CFs have a longer average life
>than T-8s. Again according to the Philips and Osram/Sylvania data sheets,
>CFs have a typical average life of 10,000 - 12,000 hours, not much better
>than T-12. They are high-output types after all. But they do keep a lumen
>level close to 95% of initial for their entire lifetime, so they also 
>should be replaced only when they fail.

I run two 55w CFs on two 20g tanks. They are currently hamilton bulbs but I
will be changing that when I replace them. They have noticeably less light
output now than they did when they were new about 1.5 years ago. I would
suspect hight temeratures in the hood, but I use a fan and the tubes run at
about 49 C (measured just a few minutes ago, on the surface of the glass
between the tubes with a lab thermometer). I understand that 1.5-2 years is
about typical for these bulbs.

>MHs have a large range of avergae lifetimes, but most of the interesting
>types fall in the range 10,000 - 15,000 hours. HPS and MV are the only
>ones that beat T-8s, with average lifetimes of 24,000 hours. There are a
>few T-8s rated at 22,000 hours though.

My MH bulbs are 400w Sylvanias rated at 36000 hours (they are only 4100 K
bulbs). I use them to grow terrestrial plants. I have one bulb that has
about 3 years on it and it still works great, but was retired anyway and is
kept as a spare. The replacement was not significantly brighter, but that's
just by eye -- it was a slightly different hue though, more greenish. I
have not used MV lighting.

>That's what I can gleam from the manufacturer's data. What could be causing
>your light setups to blow off so quickly ?

I suspect heating issues, and probably some power problems (I do tend to
have a lot of spikes in the mornings and evening, and high line voltage --
122-123v -- all day). My CFs seem to get about the expected life, MH is
fine, but I don't have the T8's lasting as long as is to be expected. I am
aware it is contrary to published data. There is an archived discussion on
the krib about decreased lifespans for T8 lights when operated at elevated
temperatures over extended periods of time. I am currently setting up a new
tank use a trio of 175w MH lights since for me they last the longest and
are cheapest to operate. I also happen to like the neat effects they
produce, but that is totally a personal preference.