This is my DIY 4Gal Pico Reef metal Halide Fixture
It use an Automotive HID bulb fitted into a Jali 11" Aluminum
light fixture, sitting directly on top of the 4 gallon glass tank.
From this video, you can see the nice shimmering effect ,
The heat is controlled by an Retro fit 2" fan. The fixture run cooler then before when it was a 18W PC without a fan.