Since I have two fixtures side by side, I did a little comparison at the 14 month mark. I changed all of the bulbs in the left fixture and left the old bulbs in the right fixture. When the lights came on, I used my NASA calibrated eyes to check the difference between the two. The bulbs at 14 months were much dimmer than the new bulbs and the color spectrum had certainly shifted. The very next day, I changed the bulbs in the fixture on the right and will put my bulbs on a 1 year change rotation. They may last much longer than I have used them, but they don't last forever.