Operating Costs
Find your kWh charge on your electric bill. Assume you have a 1,000 W light and your kWh charge is $.05/hour. A kilowatt (kW) equals 1,000 W, therefore it will cost you $0.05 cents per hour to run that light. Here's another example. Say you have a 400 W light and your kWh charge is $0.03. Since 400 W is not a kilowatt, you must divide 400 by 1,000 (0.4 kW) and multiply that by the kWh rate from your electricity bill (0.03 kWh), leaving you with a cost of $0.012 cents per hour.
Lumens Per Square Foot
To determine how many lumens per square foot you have, find out the square footage of your space by multiplying the width and depth. Divide the lumens available by your square footage. This will give you lumens per square foot. For example, say your space is 3 feet deep by 4 feet wide, for a total of 12 square feet. The total lumens available from your light(s) are 45,000 lumens, which means you have 3,750 lumens per square foot.
How Many Watts Do I Need?
The general rule of thumb for providing light for an area is a minimum of 30 W per square foot. 50 W per square foot is optimal. You can determine the proper lighting for your area by using this formula:
Watts x Square Feet
For example, say you have an area of 10 square feet and a 30 W. That would mean you have a 300 W per square feet minimum. Also, remember that fluorescent's are weaker and emit less light than an HID. This means you will need 5 times the amount of wattage to equal the output of an HID. So, 30 W of HID would equal 150 W of fluorescent's. This is why it is advised to provide a minimum of 30 W per square foot for HID lights and a minimum of 150 W per square foot for fluorescents.
