# How often to replace PC bulbs?



## therizman1 (Jul 1, 2006)

How often should these be replaced?

Also, how often would you replace T5 bulbs in comparison?

Thanks.


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## SammyP (Apr 26, 2006)

i asked the ah supply guy about this and i think he said they last for over a year. 
i'm pretty sure the T5 bulbs dont last as long as that but i cant be certain.


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## BSS (Sep 24, 2004)

The concensus of most is that PC bulbs are good until they burn out. They may lose a little intensity early on (at least to the naked eye), but supposedly they hold the intensity pretty well after that.

I just had my first bulb burn out after around three years.
Brian.


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## JenThePlantGeek (Mar 27, 2006)

Ditto to Brian - don't replace PC bulbs, you'd just be wasting your money. Use them until they pop. 

NOF are another story.... their useful lifespan is less than a year.


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## therizman1 (Jul 1, 2006)

Thanks for all the replies... I was under the impression they were only good for a year or so max like NOF.


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## Canoe2Can (Oct 31, 2004)

Manufacturers recommend changing out HO T5s every two years, 18 months for actinic (as if that matters to us). As for regular T5s, I'm sure that they are good for at least a year. Judging from the various recommendations I've seen from manufacturers, who have an interest in selling more product, any tube run off an electronic ballast should be good for at least a year.


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## Rex Grigg (Dec 10, 2002)

One more time. A T5 and a PC are the same animal. The PC is just bent or folded.


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## Ryzilla (Oct 29, 2005)

I think there is someone on this forum who has a meter to measure the lights output and has concluded that they are good until they go out. Which meens the life span of the bulb. I think I will use mine until they cease, but I will have backups waiting for that day.


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## ianiwane (Sep 7, 2004)

T5HO should actually last longer than PC. They are a straight PC and run cooler for this very reason. The cooler they run the longer they should last.


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## kzr750r1 (Jun 8, 2004)

Just replaced my bulbs over the 55g, they didn't burn out but were noticeably brown comparing new to old.

The best part about the replacement is within the next day the tank looks like a Champaign bottle. Pearling like mad! So, from now these bulbs will be replaced every 12 to 18 months. 2.5 years was too long and the tank suffered (or my patience) from my waiting for them to burn out. Now I’m on the low end of the WPG rule so YMMV if more bulbs are over the tank.

I have only 2-54w so once they start going south there is no others helping keep the growth consistent. It began to get discouraging; hence the change to see what happen.


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## snafu (Oct 9, 2004)

JenThePlantGeek said:


> Ditto to Brian - don't replace PC bulbs, you'd just be wasting your money. Use them until they pop.
> 
> NOF are another story.... their useful lifespan is less than a year.


ok. this is something i hear quite often, and i find it a little hard to believe. so... there is negligible spectrum shift and decrease in light intensity in PCs over time? can someone please point me to any data regarding this? lastly, can someone please explain the differences between the degradation mechanisms (spectrum, intensity, etc) for a T5 bulb (or PC) versus a T8 or T12? do they use different phosphor, emission mix, internal gas, electrical characteristics (e.g., current) etc? thanks again.
-snafu


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## Architect1 (Feb 19, 2006)

I find it funny you ask that because I'm always asking that question to. I hear so many different times. Like 8 to 12months it’s funny that no one can really tell you. I would say replace it once you notice your plants aren’t growing as good as they use to. Minimum 8 months and max 16 months. Depending on the bulb and what type it is.


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## kzr750r1 (Jun 8, 2004)

snafu said:


> ok. this is something i hear quite often, and i find it a little hard to believe. so... there is negligible spectrum shift and decrease in light intensity in PCs over time? can someone please point me to any data regarding this? lastly, can someone please explain the differences between the degradation mechanisms (spectrum, intensity, etc) for a T5 bulb (or PC) versus a T8 or T12? do they use different phosphor, emission mix, internal gas, electrical characteristics (e.g., current) etc? thanks again.
> -snafu


What may be going on here is Jen is using ALOT of light over a tank to begin with. At 3 to 4wpg the plants may just slow down a bit. Where I'm at it's already bleeding edge for a high light tank so any extra is always a plus. If I had 4x54w over this tank I'd likely not be replacing them just yet. Who knows? Sorry I have no technical data to provide, just personal experience.


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## plantbrain (Dec 15, 2003)

I had 520 umol /m^2/sec with new PC's and 450 after 4 years at 4" away from the bulbs, some reflector lime from water splashing etc, crust on bulbs, but there was little decay.

I run till they die.
Triton NO's FL's the same way

As long as the shift to less light is slow, most folks have plenty if not too much light as it is, then things are fine.

I've sugegsted that new tanks with new lights have issues because the light bulbs have not yet decayed and are adding too much light, obviously there are other issues going on........but.........this can help make it worse.

Regards, 
Tom Barr


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## Kicker (Jul 17, 2006)

So it's not true that the local petshops telling me that T5's penetrate the tank better than PC's?:eek5:


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## chiahead (Dec 5, 2005)

plantbrain said:


> I had 520 umol /m^2/sec with new PC's and 450 after 4 years at 4" away from the bulbs, some reflector lime from water splashing etc, crust on bulbs, but there was little decay.
> 
> Regards,
> Tom Barr



I did some testing a while back and got pretty different readings. I am not using a great lux meter but here was what I found. 

PC bulbs about 8 months old-2800 lux
New PC-3800 lux

I am no light expert or even a planted tank expert but once I changed them the plants grew in much better and full. Now I try to change every 8 months or so.


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## plantbrain (Dec 15, 2003)

Well a lux meter is a poor method for testing PAR that is specifically calibrated to measure precisely what range plants use for photosynthesis.
Your light meter in your camera measures lux which is generally 555nm range.
Few plant biologist use lux, virtually all of them use PAR.

That's comparing apples and oranges.
Also, did you clean the bulbs really good and the reflector etc?

Please send me those 8 month old bulbs
I mean it. I am going on 5 years on some now.
Don't throw them away, they are just getting "broken in".

Kicker,
A PC is simply a bent T5.
You have less heat, less restrike, so a little more efficient light use, but they penatrate the same.

Regards, 
Tom Barr


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## snafu (Oct 9, 2004)

plantbrain said:


> I had 520 umol /m^2/sec with new PC's and 450 after 4 years at 4" away from the bulbs, some reflector lime from water splashing etc, crust on bulbs, but there was little decay.
> 
> I run till they die.
> Triton NO's FL's the same way


thanks for the data points. that is an interesting point you bring up regarding other FL bulbs (i.e., Triton NO); specifically, you can generally use a good quality FL bulb until it dies. the 'Rated Lifetime' numbers are generally given by the time a certain percentage of a bulb lot are still operating (say half) and isn't necessarily correlated to output levels or spectrum.

in a 5 minute search of FLs (ref 1), it appears smaller diameter bulbs often use different phosphors (rare-earth versus halophophate), which have better lumen maintenance, color rendering and lamp efficiency. RE phosphors also can withstand higher arc power per unit of phosphor area. the reference mentioned most FL with diameters of an inch or less (e.g., some T8, T5, PC) use RE phosphors.

Lighting Market Sourcebook
ref 1: http://enduse.lbl.gov/SharedData/LightingMarketSourcebook/appAtbl.DOC
from Table A.5, cont. (Lumin Maintenance)
*
Four-Foot Tubular Fluorescent: T12 Lamps*
Lumen output typically declines by about _20-25%_ over rated lamp life

*Four-Foot Tubular Fluorescent: T8 Lamps*
Lumen output typically declines by about _10-12%_ over rated lamp life. Lamps using RE phosphors can withstand a higher loading (arc power per unit of phosphor area) and thus provide better lumen maintenance than standard-phosphor lamps 

*Compact Fluorescent Lamps (CFLs)*
Typically, lumen output is reduced by _10-30%_ over the rated life; lumen maintenance improves with lamp size

Generally, what this tells me is that (from an output standpoint) FLs can generally be run until they die. Still not sure about the spectrum shift. 
-snafu


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