[AaronT]

I've been using T5 lighting for a few years now. Good bulbs will definitely last two years. It's probably a good idea to replace them after two years though. They do lose a little bit of punch, but not much.

 

[AaronT]

Hagens website recommended replacement after 6-8 months. Of course that might have been to encourage the sale of more bulbs, who knows.

My guess would be that's to sell more bulbs, or their bulbs aren't up to par.