Usage drops at night, not the price. And how much it cost you depends on what you pay a kilowatt hour x the hours the light is on. You can find how much each type lamp uses doing a search. i.e. my T5 uses approx. $20.00 a month 24x7. A thousand watt example - 6 hrs x 1100 watts (a 1000 watt uses that) divide by 1000 x $ 0.04 per kwh x 30 days = $7.92. :thumbsup: