Next question is in regards to bulb longevity. Just about everywhere I've looked it is recommended to change the NO tubes every 10-12 months. Why is that? The box the tubes come in all say they are good for about 10,000 hours. Now, if I run the lights for 10 hours a day then they should remain effective for about 2.75 years! To be on the conservative side you could replace every 2 years. Why do they recommend every 1 year???