Ballast question - Might be a stupid question

[I have a Magnetic 175 watt MH ballast that pushes two bulbs. Currently I am only using on bulb. I just unplugged the other cord from the ballast? There is only one on and off switch on the ballast. My question is, am i using the same amount of energy as the two bulbs running, even though only one is hooked up.]
 
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