Question
Hey guys, I have a two tube shop light set up same as on your video. How often should I replace those tubes?

Answer
The tubes tend to decrease in intensity over time.  You should replace them yearly, or when you notice them dimming.  Ironically, sometimes the ballast will go out before the tube does.  At least that's how it goes in a wet environment such as our greenhouses.

Good growing!
Jacob Farin