Replacing bulbs for planted tank... When?

[Hholly]

So I've heard that fluorescent bulbs for planted tanks need replacing every year even though they still light up. Has anyone ever tested to see if they still grow plants well beyond a year? Can you start to see problems in your plants when it's time to replace them? I hate to throw away perfectly good tubes if they aren't that bad yet. Just interested in what everybody else does or if anyone has experimented with it.
TIA!

 

[fort384]

You start to see a shift in provided spectrum as time wears on, and algae growth can become more prevalent. It has been documented that there is significant loss in PAR over time with fluorescent bulbs, even though the bulbs continue to provide visible light.

 

[Hholly]

So it's pretty much right at a year when the drop off occurs? I wonder why it happens?
Thanks!

 

[fort384]

No, it isn't a huge drop, all at once. It is fairly linear. The minute you turn it on the first time, it starts to lose PAR. A year is usually the suggestion for a t5ho as a happy medium. I personally replaced mine at more like 8 months when I ran them. I have heard of others going 18 months.

The reason is, the phosphors that provide luminescence in a fluorescent lamp degrade over time due to oxidation and other factors.

 

[Hholly]

Fort, you're so smart. Thanks!