I bought a new ballast for my Ott Light when it began to get dim and a new light bulb didn't fix it. The company sent it very promptly and the light has continued to work great for the 3 or 4 years since I got it.
The ballast is in the short length of cord that plugs into the wall. I believe that the newer lights may have their ballast built into the light area, which means it can't be replaced when it goes bad, so those won't have the cord that comes in two pieces.