When your fluorescnt bulb don't shine so bright...anymore

6 months if you have them on 10-12 hrs a day every day. I've heard that the black line (burn mark?) around an end (just inside the bulb) is also an indication that it has burned past it's usefulness.

I'd say if you notice an appreciable difference in the colour/amount of light, it's time to replace the bulb. PC bulbs last longer than NO fluorescents, the general 'rule' seems to be that NO bulbs last about 6 months, as beviking said, and PC bulbs need to be replaced at around 24 months (some say 12, but the plant gurus here seem to get good growth with theirs up to two years, and I trust their experience and recommendations).

2 years out of a PC bulb...oh good news to hear...can you post a link to where you read this info..I would like to learn more about it..

I change my PC's on my reef tank every 12 months...although you can probably get more out of them growth wise, I am always amazed how much better the tank looks when I change the bulbs after 1 year of use - you don't realize the drop off when you see the tank every day. Its worth it to me to have my tank looking its best! This is true for my freshwater tanks too - new bulbs make the tank look more vibrant!

Grey Legion said:

2 years out of a PC bulb...oh good news to hear...can you post a link to where you read this info..I would like to learn more about it..

Click to expand...

If you search the planted tank section for PC bulb and replace, I'm sure you'll find the threads - there have been several over the last few months.
[edit] Went and did the search myself, found this but not the other thread Len refers to... I'll keep looking [/edit]

Heres a bit more info than you requested but I cannot help but drive something into the ground .

Well florescent bulbs do lose intensity. Very much so. It starts as soon as you plug them in and becomes apparent when compared to a new month as soon as a month or two. after about 6 months to a year (at 12hr/day) they lose upwards of 50% of thier intensity. You can continue to use them but double the number of bulbs. but then your burning double the electricity. Cheaper probably to get a new bulb.

This is because the phosphors in them slowly burn out. Florescent bulbs actually generate UV light (dangerous amounts btw never run a "clear" sterilization bulb without protective covering). This UV must be converted to a safer and preferably visible light. This is what the white powder on the inside of the bulbs does (the phosphors). this is a mixture of several different chemicals that glow red blue green and shades in between. higher quality bulbs has a better tuned phosphors for whatever purpose it was designed for (high in red and blue for grow light, more even distribution with a small amount of UV bleed through for a full spectrum etc, UVA discharge for black light etc). as these phosphors do thier job they lose efficency, emitting less and less light until they "burn out" (the black ring near the emitters as an example) Total florescent failure is usually due to the emitters burning out.

To make things even more interesting. As a bulb ages, the phosphors burn out at different rates. This causes color shifts. Look up at the bulbs at walmart. Older ones will have a bluish or more likely a reddish tinge. Of course these color shifts for actinic(sp?) and grow lights can be devestating to your micro environment. I've heard stories (more likely myths since i cannot verify online) that in really old bulbs the black ring near the end will burn through causing the UVB-UVC rays to leave causing nastiness. Of course if that was true, they would have a warning label. Flipping through a car manual in my friends car recently said "do not operate while sleeping" hmmm.

You can use the old bulbs in things like desk lamps etc where the illumination is still sufficant. or i guess you could donate them to a church or something. I hate to throw something away that is still "good enough for me"

Helped a friend with a 55G acrylic SW with a quad CF set-up hood.
When we plugged the lights in to check them, the lights were really dim!
So it looks to be the CF's can dim but not totally burn out.

I have been runnign screw in compact fluourescents in my 10 gallon for well over 2 years now and they the plants are still taking over. The colour may be affected a bit but neither I nor the fish seem to care too much. It seems like too much of a waste to me to throw out useful bulbs. If they start to get dark patches on them I will throw them out.