here is a light/power calculator...
BC Hydro - Power Smart for Business - Online Lighting Calculator
You can also use this...
To calculate cost: multiply bulb wattage (WT) times hours of operation (HRS) and divide by 1000. This equals the number of kilowatt hours of electricity consumed.
Example: a 400 watt bulb running 18 hours will consume 7.2 kilowatt hours (400 X 18 / 1000)
check your power bill for the cost of each kilowatt hour. You can then multiply the number of kilowatt hours by the cost of a kilowatt hour to determine the cost per month.
Some examples (assuming a price of .04 per kilowatt hour):
A 400 watt light fixture running 6 hours a day:
6 HRS X 400 WATTS \ 1000 X .04 X 30 (days) = $3.31 per month
A 1000 watt light fixture running 24 hours a day:
24 HRS x 1000 WATTS \ 1000 X .04 X 30 (days) = $28.80 per month
The formula is:
Bulb Wattage = WATT
Hours of operation = HRS
Cost per Kilowatt hour (should be represented in cents like .04 or .06)= .KH
the 1000 is part of the formula
and the 30 represents days in a month
FORMULA:
WATT X HRS \ 1000 X .KH X 30 = cost per month
So you would read that as Watts times hours divided by 1000 times cost of kilowatt hour times 30 days equals cost per month