Does a metal-halide lamp fixture use power if the bulb is burnt out? If so, how many Watts would a 277 V, 1,000 W fixture draw with the lamp burnt out? Transformer is in-line between the 480 V 3-phase supply and the light switch.
The simple answer is "Yes, it may use power".
How much power will depend entirely on the design of the ballast or control gear, and could range from a negligible power draw for smart electronics that recognise that the lamp is failed and just sit there, to something more substantial for gear that keeps trying to restart the lamp. If this answer is important, I suggest asking for information from the manufacturer of the fixture or the control gear.
I found the below link to be very helpful, they have provided clearly the power required for metal halide lamp fixture. http://www.hoveyelectric.com/hovey-electric-power-blog/bid/85127/How-To-Calculate-Lighting-Costs-For-Metal-Halide-Fixtures
The link provides this list of typical metal halide power consumption:
175 Watt Metal Halide Fixture = 205 Actual Watts
250 Watt Metal Halide Fixture = 290 Actual Watts
400 Watt Metal Halide Fixture = 458 Actual Watts
1,000 Watt Metal Halide Fixture = 1,081 Actual Watts