One retailer told me that they should be replaced every year when using them for the late fall through early spring season. However, I noticed as I was buying my T8's today that they have a much longer life span (like 8 years, lol...).
So was the retailer just trying to move product or was he right?
the life span for the bulb is 8 years but the lumens drop off quite fast after a year of yse for most flouresent bulbs and its common practice to replace about that time...t5 's I dont know about for sure but other types yes ..this is a good rule of thumb for hid like mh and hps too
Dont know too much for orchids but been in the saltwater reef tank hobby for years and figure lights are lights regardless of hobby. Best bet for T-5 life span is best replaced after 6-8 months if money permits. If you want to push it you can go a full year but by that point the bulb has been beaten to death.