Is it just the strip light and not the full hood? If so you may consider getting another one and placing both of them on the glass top. I've done this many times with good results. With just the strip light its easy enough to life it up and place it atop the other one when you need to access the tank. With a 20gal you should be able to get a used light strip cheaply enough.
Also make sure you are changing the bulbs between 4-6 months. They can and will last longer but they are not nearly as effective.
