Not all lights are water-resistant (In fact, most are not). I know for sure that the Fluval Marine 3.0 and the Current USA lights (the bar shaped lights they sell) are, but most of the high end options like AI Primes, Kessils, Radions, etc are not water-resistant in the slightest.Wow, that's amazing that your hob tank made it through one of your summers!! Now I'm back to undecided. I thought I had mailed it down to a mesh lid but now I'm not so sure. Haha. Ironically I already ordered the clips to hold a glass/acrylic lid awhile ago. Then I wavered and was leaning toward mesh. Now I'm back to possibly glass or acrylic. I like the idea that was mentioned of cutting an opening for lights in a glass or acrylic top so they fit right in. I'm assuming they're water resistant and you wouldn't lose any PAR.
Also, most lights have an ideal mounting height based on the size tank you're using. For instance, an AI Prime should be mounted approximately 10" Above the surface of the water for a tank 18" Wide and wider for the best PAR distribution. For tanks 12" wide it should be brought down to 8" above the water. If you go lower than that you have a really hard hotspot right in the middle of the tank and very little light out towards the edges. BRSTV does a LOT of lighting tutorials/reviews and they have recommended mounting heights and spectrums for a lot of different tank setups.