I have 8 4' double bulb T-12 lights going 24x7 in the basement.
Could someone give me an indicatication of the daily cost of running a single 40 watt 2 bulb 4' fixture 24x7 for a month?
Costs equal total watts used divided by 10,000 if your electricity is 10Â¢ per kilowatt hour.
Your electric rate may vary, but at an average rate of 10Â¢/kWh you'd be looking at ~80W * 24 hours * 30 days / 1000 * $0.10 = $5.76 per month. Running eight fixtures would be around $46 per month.
Is there a reason you're running them 24 hours a day?
Under the premise that more must be better since the plants aren't getting sunlight equivalents.
Am I causing harm?
Plants also need a rest period. If you are only running them 24 hours for a couple months until they will go outside then that would be ok for most plants but not all.
Some power companies have gradually increasing charges per KWH the more you use. Running fourteen 32 watt tubes pushed me into the 24 cents per KWH excess usage bracket and increased my bill by about $20 a month, and that was using them only about six hours a day, and putting my plants out on the patio in the sun the rest of the time, or letting them sleep indoors. My basic electric charge is 12 cents per KWH.
Don't overlook the power consumption of ballasts. I just recently noticed that my ballasts made by Advance Electric Co. run much hotter than those made by Westinghouse. Obviously, not all ballasts are created equal, but usually an extra 10% power consumption is assumed.