Does the bulb say the wattage on it? You could measure the current draw with a multimeter that has a clamp on current capability. It should be around 8.3Amps if the bulb really is 1000W. The meter would just go around one of the wires, which should be accessible near the socket.

If you have a spare bulb try that out. If you don't this may all be moot since the Thorn bulbs are not available new anymore. I don't know if there's a good replacement in that wattage. The smaller ones are rare.