Light Lifespan

[dewilde2]

How often should you replace your bulbs? Is there a point at which they may still turn on but no longer be helpful for your plants?

[malken]

I have wondered this myself. My 96W cf bulb has been there since I set up the tank originally. I'm not sure exactly how long it's been but I think I'm looking at three years without changing the bulb. My plants are still thriving (with the exception of the occasional plant that dies fairly quickly. The bulb was supposed to expire after one year.

[Ajordan]

There was an interesting little tib bit in the letters to the editor part of Tropical Fish Hobbyist's most recent issue. A reader wrote in with some information about fluorescent lighting degradation curves. The comments were brief but the idea was that CF bulbs spectrum degrades quickly after one year while T5 and T6 lights see a quick degradation (a small one) then remain 'good' for most of their life...

[ansbfish]

I think most people say to replace them every year, I don't have much experience with fluorescent lamps yet, but I'm planning to run mine till they burn out.

[vanillarum]

I was in my lfs today, reading light boxes (I'm thinking of adding another tank to my collection and was trying to decide which light I would need). The box said that bulbs should be changed once a year 'cause they lose their effectiveness. Just FYI.

[Cory Keeper]

I'm not sure how true that is vanillarum. Yes they do lose their effectiveness, however, do remember that they are out to make a profit, and if you alot of these bulbs, you could be looking at $75+ every year. Tubes do have whats called Cathodic Degradation, and over time these cathodes can lose their effectivness as time wears on. If the bulbs were run 24-7 I would say 1 year sounds about right, but 2-3 years is probably closer to when you actually need to replace them.

for more info, try this
http://en.wikipedia.org/wiki/Fluorescent_lamp

[Ajordan]

I think its wise to be weary of what could be marketing schemes but I think 2-3 years is probably on the long side of when you would want to replace bulbs (depending on type and usage). I replaced my CF 65w bulbs recently, one was about 6 months old and the other was about a year old. The visible difference was astounding.

While a light may still look bright after time its the 'spectrum shift' that we should be concerned with. I thought that it had something to do with the phosphors decaying over time...

[plantbrain]

I actually have several light meters that measure PAR. I also have some PC bulbs that are 4-5 years old, they run about 90% that when they where new.

That's 9 total bulbs, so not much error either due to chance.
Conclusion: run em till they die.

If you are on the real low side of lighting, it might make some difference, but most seem to have too much light to begin with.


Regards,
Tom Barr

[Mandairn]

While its ture they lose thier power over a year i think its depends on how meny plants you have and how fast you want to grow them. I my self have just a hand full and are running them till they die. Now if i had a jungle(I dont like heavy planted aquarims) I would replace them once a year.

[Canuck]

I replaced my CF 65w bulbs recently, one was about 6 months old and the other was about a year old. The visible difference was astounding.

This is the burn in period, there is a sharp decline in light output in the first 100 hours of use after which the bulb reaches its listed light output. And then a much much slower decline in light output over time, a quality compact flourescent bulb (not the spiral incandescent replacements) will still be at 90% of listed light output when it burns out.

[bigwater]

I just replaced the 4 bulbs on my 90 and it made a big difference in both over brightness and plant growth. The bulbs were between 2- 3 years old. I also cleaned the reflectors and WOW they needed it big time. It seems that their are different experiences here, so I would recommend having a spare set on hand and trying them to see. If they do not make a difference put the old ones back in.