hps conversion bulb using more energy? help

ive been running a 400 watt MH bulb and getting like 35$ monthly electric bills.

after picking up an hps conversion bulb a few weeks ago to start flowering these plants but using the same Ballast
i just received a bill with a 246$ electricity cost!

Could this be from using the new bulb for only 2 weeks at most???

Im hoping it is a mistake!
 
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