I used a similar concept for a "sit-on-top" light fixture. It's purely functional and ugly as hell, but normally covered by the canopy hood. I can open the hood and move one light fixture out of the way with this setup for maintenance. Shown is the "up" position without the hood on. The light fixtures rest on it's own arms in the up position like your's does in the down position. The only reason I brought it up is that no latches are required. This works out well for fixtures that sit on the tank, rather than attached to a wall. It worked out well for me. I wanted to be able to clean the tank with some light on it. I worked out a more elegant solution, but never built it. I tore down the tank several years ago and am now using a different set up.
http://home.pacbell.net/jrplanck/hoodup.jpg