In article , Ignoramus5455 wrote:
I bought some metal halide lights off ebay. $50 apiece, used. I am
taking some risk. They are enclosed with a glass. I will keep this
NG updated about them. I might install one light in our backyard,
instead of the 500 watt halogen light -- I'll see how it goes.

I do want to mention that a 175 watt metal halide usually outperforms a
500 watt halogen. A 100 watt metal halide is a little dimmer than a 500
watt halogen but a little brighter than a 300 watt one.
However, metal halide has a spectrum more favorable to night vision than
halogen or other incandescent. For outdoor illumination at night, a 100
watt metal halide may be as effective as a 500 watt halogen.

A couple things to keep in mind:

1. You may not get superior performance from metal halide unless the
fixture directs light in a manner similar to that of the halogen fixture.

2. With higher output and with light that is more white or more bluish,
light pollution is of greater concern. You should get a fixture or make a
fixture that has all of the light hitting the objects or the ground rather
than going skyward.

- Don Klipstein )