I bought a 150Watt Metal Halide setup for supplemental light for my little hobby greenhouse when it was inside last winter and the bulb is very blue.
In fact I have two other normal daylight spectrum compact fluroescents in the same GH. When they are on my Cochleanthes aromatica 'Magnifica' has purple on the lip [as it does in any normal daylight or household light] but at night if only the metal halide is on, the purple is gone and instead it is blue!
I believe it is a marine bulb, but the setup was sold for growing plants in freshwater aquariums.
Either way I think it has really helped my orchids and even induced some to bloom that wouldn't have otherwise.
