Hi Shawn,
" I was wondering, how often these T8 lights need to be replaced? "
I only use my T8 fixtures about half of a year, when I am doing my indoor gardening. I don't use them during warm weather when I am gardening outdoors.
I haven't noticed any decline in their light output over the years. One does occasionally burn out, but that is an exception. They are rated at 20,000 hours of service. Many of my original bulbs that I purchased in 2005 are still in service.
And I have been overdriving many of them. I assumed that since the overdrive modification effectively doubles the light output, that it would halve the bulb lifetime. That is apparently not the case. Over-driving probably decreases the bulb life some, but apparently it isn't a drastic decrease. I am still quite pleased with my T8 shoplights. I plan to make the over-drive modification to some more of them in the next few weeks.
Happy New Year !
ZM
