# Life expectancy of a Fluorescent tube



## thisandthat (Jan 6, 2013)

A typical tube lasts 20k hours +
http://www.usa.ecat.lighting.philip...cent-lamps/t5/t5-high-output/927993186522_na/

And they cost about $8

So why is it that a $24+ aquarium tube is supposed to be replaced after a year
At 8 hours that's under 3000 hours.

Seems fishy.....


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## Seattle_Aquarist (Mar 7, 2008)

Hi thisandthat,

Welcome to APC! 

I can answer that one. Although my fluorescent tube still lights up after a year the light output (measured as PAR) has dropped by 40% after one year of operation.


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## thisandthat (Jan 6, 2013)

Ok, 

Are you saying your normal house hold lights went down 40% or your aquarium ones?

Do you figure it continues to drop 40% year? 

When you say PAR are you saying everything between 400 and 700 nanometers dropped 40%?
That would be pretty visible difference wouldn't it be?

Or just the peak chlorophyll b and a values at 410, 420, 453, 642, and 662?

Still seems like a bit of scam that they can make a 5600k bulb throw out the same visible light for 20,000 h but not a grow light.

Thanks for the quick response.


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## Seattle_Aquarist (Mar 7, 2008)

Hi thisandthat,

I took PAR readings at the substrate level in my aquariums. I didn't bother to test after a year; a 40% drop is enough.

PAR by definition is the entire 400-700 spectrum. I didn't notice the drop in output until in put in new bulbs and they were definitely brighter.

The bulb may last 20,000 hours before it burns out; that does not mean that the output will remain constant during that period of time. 

You may want to look into LED lighting if you don't want to replace bulbs annually.


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## TropTrea (Jan 10, 2014)

Having worked in the quality control end of the lighting industry for several years I can see the argument on both sides of this.

From day one florescent tubes begin to slowly deteriorate. If you were to run them on spectrometers and graph the changes you would find that most of them slowly shift to the longer wave lengths and the K temperature of the bulbs slowly shifts to a lower level. The change is so gradual that it is not noticeable by the naked eye.

Dependent upon your use of the bulb will determine how long it will be useful for your purposes. A majortity of bulbs are used for room lighting. With room lighting the biggest factor for bulb life span is the amount of lumens they are producing. Lumens are weighted to green part of the spectrum which has the least amount of change over time. Therefore to get 30,000 hours out of a room light is very acceptable.

As the bulb deteriorates the blue end of the spectrum is what deteriorates the fastest. With plants or corals are main concern is the red and blue end of the spectrum. After X period of time the lumens of the tube may decrease by 5% total which is not considered critical by any means for room lighting. However in reality at that point the loose may have been 2% to both the red and green parts of the spectrum but 11% to the blue end of the spectrum. Since the eye is not as sensative to blue light as it is to green light we never will see the 11% loss of blue light. But that blue light is critical to plants and especially to one with corals. 

For people with Reef tanks and corals the blue end of the spectrum is the most important there is. Some corals only need blue light. Therefore it is not unusual for them to change bulbs every 6 months. For people with fresh water plants the blue light is also critical but not nearly as critical as the coral people. Most of us can live with the loss of blue light, especially in a well lite tank for longer than the coral people. But defiantly not as long as the people that are simply lighting up a room.


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## Seattle_Aquarist (Mar 7, 2008)

Hi TropTrea,

lol, I will mention to Erik (thekrib.com) that you posted. I see him monthly at the GSAS meetings.


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## Michael (Jul 20, 2010)

The experts have spoken! Change those tubes after a year.


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## bpb (Mar 23, 2011)

Yearly replacement is a good idea, unless even at 40% par reduction, you're still in target par ranges, though the specral shift may cause more algae than plant growth. As far as houshold fixture bulbs throwing out the same visible light for 20,000 hours? Not even. It's night and day difference when I swap out the spiral CF bulbs in my bathroom fixtures, or even the 3000k T8 tubes in the kitchen lights. It's like twice as bright as the old bulbs. Intensity does in fact drop and spectrum does shift. New fluorescent bulbs are always much brighter and crisper/bluer than old bulbs, no matter what the application


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