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Discussion Starter #1
Hey,
I have had these two old 18W T8 Tubes for more than 2.5 years (one of them maybe even 3.5).
Is it possible that though i cannot recognize it, the light produced has gotten "weaker"?



Thanks guys.
 

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IMO, it is always best to replace bulbs at least once a year. Bulbs lose their effectiveness over a period of time, some types faster then others. I'm sure you will be able to tell a big difference when they are replaced with new ones.

I use to think I could run PC bulbs until they burned out, due to the fact this is what others where saying. But after several years of running them, I decided to replace them. A side to side comparison showed a big difference in the old & new bulb. The old bulbs was yellowed & black at the ends. The huge difference came when the new bulbs where turned on over the tank. I was very surprised how dark the tank had became with the olds bulbs. Which really could not be seen until they where replaced.
 

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I know T12s lose 60% in 6 months.

I have always changed T8s and CFs annually.

Supposedly T5 HO linear can go 2 years but I havent experienced that myself.

The cathode tube decays over time and output diminishes dramatically and the spectral output can even shift.

If the ends of the tube are blackened then it is past time to change them out.
 

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Discussion Starter #5
okay, i've bought new T8's.
Same watt rate. seem to work fine.
I think i can tell a slightly better light than the old one.
But it could have something to do with the colour (new one's are 865).
 

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Sounds like a Philips number (865). This would be a 6500K bulb if, indead, they are Philips.
 

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After so many years your bulbs will still use up the same watt. Saying "Watt Rate" is redundant because watt is a rate, 1 W=1 Joule / second. AFter 2.5 yrs of normal rate your bulbs are still consuming that same amount of power (Watt) but the lumens/watt and the color will have shifted. After 2+ yrs of use your T8 bulbs has probably lost 60-70% of the lumen output.
 

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1 watt-second = 1 joule; (1 watt-hour = 3600 joules); 1 newton-meter = 1 joule: therefore 1 watt-second = 1 newton-meter.

You should express the light loss in intensity lost. Lumens is meaningless to plants and is an output value of light in the green area of the spectrum that was designed for the human eye.

 

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Discussion Starter #9
That was all very interesting to read, guys!
Here is a picture of the new bulb:



Osram Cool White 18W, 865, 1300Lm.
It was the best the shop had for planter aquarium as far as I could tell.
I also bought Anubis that turned up as I unraveled it, that had three nice rhizomes.
Here are a few photos from after the redesign.





BTW, i guess that i'll need to get at least 90W of light for growth of low-tech plants right?
180L, only fertilizing once in a while with Sera Florena and planted JBL's "7 Balls" near the roots.
 

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great look tank and I like your tank driftwood setup. I was wondering the same thing on bulb life. I bought a used tank setup and it has t8s that are well over a year old. Time to go to the store! and I might as well pick up some t5's for my other fixture.

Does anyone know about light outputs for the spiral florescent bulbs?? they're supposed to be good for 10yrs or something like that so what about their output??
 

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Hi EQUINOX,

According to GE Technical Pamphlet TP-105 typical lumen loss is -10% at 1,500 hours use; -20% at 2,500 hours use; -30% at 5,000 hours use; and -40% at 11,000 hours use. So after a year of 8 hours use per day, your lumens are reduced about 20%.
 

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Discussion Starter #13
great look tank and I like your tank driftwood setup.
Thank you very much!
It took me awhile to think of it but now there's no other way I can imagine arranging it.

Hi EQUINOX,

According to GE Technical Pamphlet TP-105 typical lumen loss is -10% at 1,500 hours use; -20% at 2,500 hours use; -30% at 5,000 hours use; and -40% at 11,000 hours use. So after a year of 8 hours use per day, your lumens are reduced about 20%.
Just to make sure: this is relevant to T8 bulbs?
Thanks.
 

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If you Google GE Technical Pamphlet TP-105 you can easily find it. It is easy to read but bear in mind that cathode tubes are a bit different for each manufacturer and can also vary for the type of bulb it is in.

Also, you dont necessarily want to go by lumens lost (or lumens alone) as this is a scale designed for the human eye in percieving brightness which falls/peaks in the 500nm area of the spectrum and is basically green light.
 
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