When to replace lights

[Ross]

For those pondering when to replace florescent lights (in this case t5 straight 47" tubes) consider this:

I measured FCs with calibrated meter on tubes set up last January and got 800 (or so) FCs. Actually a bit less, like 795.

I just replaced all four tubes and measured (at same point with same meter) and got 1380+ FCs! That should be a signal to replace bulbs more frequently than the manufacturer states. I had less than 6000 hours and they were rated at 10,000 hours. Who knows when they first started dropping off? I plan to check weekly now,