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Old 10-29-2010, 12:06 PM
NorEastFla NorEastFla is offline
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Join Date: Aug 2010
Location: North East Florida
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Oh my goodness, the original question has seemed to have gotten lost in a massive amount of extra information.

Let me jump into the fray..hehe

Ok, lighting costs are easily calculated and I can tell you how to do it with no pain or strain.

First, let me say that what you pay for is "Watts Used Per Month".

When you have used One Thousand Watts for One Hour, you have used exactly One Kilowatt.

So, if you use 250 watts for 4 hours, you have; 4 times 250 watts equals 1000 watts used in 4 hours. So, you have used One Kilowatt in 4 hours.

If you look either on your account with your electric company or on your bill, you'll see how many Kilowatts you used for the entire month.

You'll also see how much you paid for using them as your final total bill.

Yes, I know that includes 900 taxes and fees. I don't care. You paid for it anyway.

If you divide your total bill by the amount of kilowatts you used for the month, you'll see how much each kilowatt cost you, including all the fees and such. I do this every month and it comes out to within a dollar or two of what my bill is.

Like last month:

Total Bill: 203.94

Kilowatts Used: 1994

Now: 203.94 divided by 1994 = 0.102

That means I paid 10.2 cents per/kilowatt that I used, overall.

I read my meter and do this equation every month. It's always within a dollar or two.

I see how much I used and do the math. Then I know how much my bill will be.

So, that said, a watt is a watt is a watt is a watt. One watt costs exactly what one watt costs. It makes absolutely no difference what used the watt.

Now we're at the root of the answer:

If you are using a 400 watt light, and it is really using 400 watts, then for every hour you have it on, it will consume 400 watts. If you have it on 24 hours a day, it will use 9600 watts, or 9.6 kilowatts.

If you pay 10.2 cents per/kilowatt like I do, then that light will have cost you 98 cents for each day you ran it for 24 hours.

See how easy that is?

Now, here's the proverbial monkey wrench in the works...

But, but, but....MY 400 watt hps bulb says it will put out 430 watts of light!

Ok, here's the only REAL answer to that.

I own a small meter called a "Kill-A-Watt" meter ($25). I plug it into an outlet, then plug a device into the meter. I then set it to record how many watts are being used.

I leave it on like that for exactly 24 hours to the very second.

It shows me on it's readout, EXACTLY how many watts that device used in that 24 hour period of time.

NOW I know how many watts that light REALLY uses.

From that point, it's as easy as I've shown above to figure out almost exactly how much your light will cost you each month by just doing the math.

No problemo!
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Last edited by NorEastFla; 10-29-2010 at 02:17 PM.
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