Show her that it is just a bulb in a socket. If this is a manufactured fixture or hood, there is no more chance of problems than a lamp in your home. However, if you have done any DIY
, just make sure to show her that your connections are out of the way or waterproof...and that you have accounted for the heat of these bulbs, ballasts (magnetic especially), etc.
This isn't MH
specific as much as it is for any lighting or electrical equipment around a fishtank.