The reason why the higher voltage saves you money, is because the lower current bulb will produce less heat. This should prolong the life of the bulb, as well as use less electricity. It would drop *exactly* 2 amps by the way, remember the formula P=VI, if you double the voltage, but still have the same overall wattage, the current definitely must comply with the laws of physics and be cut in half. The main reason for the savings in electricity is the heat. You may have a 1000w bulb, but that's only the energy going to produce the light, there is also heat created, which is wasted electricity. That heat isn't coming from nowhere, its being produced by electricity. The more heat you are producing, you'll climb that much higher above the 1000 watt power consumption mark. To summarize, yes, lower current with the same wattage will save you money.
