Energy Efficient Lighting:How To Calculate Cost 23 Watt Bulb

Posted by Jimmy Hovey on Tue, Jan 03, 2012 @ 11:01 AM

Is a 23 Watt Bulb Really More Energy Efficient than a 100 Watt Incandescent?

Calculating the Cost of a 23 Watt CFL

The typical replacement for a 100 watt incandescent is a 23 watt compact fluorescent bulb.  We often get the question about why someone should change out their incandescent bulbs for the CFL's. 

Here I show you a simple example and the formula's for calculating the cost of an individual CFL so you can see the benefit of making your lighting more energy efficient. Just calculating the cost and showing you the cost for the bulb would not be a convincing argument for energy efficiency. 

The numbers become very convincing when you compare the 23 watt cfl with the 100 watt incandescent. So in order to determine the cost of a 23 watt cfl, we will compare the cost of the two different bulbs.  

Both of the bulbs above are suitable replacements and can be utilized for the same application.  While the old style 100 Watt bulb will likely be cheaper to purchase upfront, over time the compact fluorescent will save you money.  How much difference? 

Finding the Difference in Wattage

How-to-calculate-the-cost-of-23-watt-compact-fluorescent-cfl

In order to find the difference in wattage, we just use simple subtraction.  Identify the wattage on the package or on the bulb themselves (Located on the top of incandescent and usually on the base of a CFL).   

In this case we are going to calculate the cost of a 23 Watt CFL and compare that to what you are going to replace, the 100 Watt incandescent.  Take the 100 Watts from the incandescent and Subtract the 23 Watt Compact Fluorescent. You will find a difference of 77 Watts.

(100 Watts - 23 Watts = 77 Watts Difference).  Simple math right?

Now that we have the wattage difference, we can determine how much each bulb costs us to operate annually.    

Calculating Kwh

Your utility company charges by the Kilowatt Hour or (Kwh).  They don't charge by wattage so you need to take the calculations even further.  In order to determine the cost difference between the two bulbs, we utilize the wattages to determine the kwh.  Here is the equation we can utilize to find Kwh:

Fixture Quantity x Fixture Wattage = Total Watts

Total Watts / 1000 = Kilowatts

Kilowatts x (Hours of Usage) = Kilowatt/Hr

Kilowatt/Hr x (Cost of Energy) = Annual Cost

So How Much Does a 23 Watt Bulb Cost?

Let's assume you have the following:

Your facility has 20 Lights (Fixture Quantity) that currently have 100 watt incandescent bulbs installed.

You are planning on replacing 100 Watt Bulbs (Fixture Wattage for Each) with    23 Watt CFL Bulbs (Fixture Wattage for Each)

2000 Hours (Hours of Usage)

$.10 Per Kilowatt/Hr (Average Energy Rate Charged)

How much does it cost annually for 20 - 100 Watt Bulbs?

20 (Fixtures) x 100 (Watts Each) = 2000 Watts

2,000 Watts / 1000 = 2 kw (Kilowatt)

2 kw x 2000 hrs per year = 4000 kwh (Kilowatt/Hour)

4000 kwh x $.10 = $400

$400 to operate 20 lamps with 100 Watt Bulbs

How much does it cost annually to operate 20 - 23 Watt Bulbs?

20(Fixtures) x 23 (Watts Each) = 460 Watts

460 Watts / 1,000 = .46 Kw (Kilowatt)

.46 Kw x 2000 hrs per year = 920 kwh (Kilowatt Hour)

920 kwh x $.10 = $92.00

$92 to operate 20 lamps with 23 Watt Bulbs

The Difference is $308 Annual Savings

Which Bulb is More Energy Efficient?

The 23 Watt CFL bulb cost $4.60 ($92 / 20 = $4.60) annually compared to $20 ($400 / 20 = $20.00) for a 100 Watt Incandescent bulb. 

$4.60 versus $20.00....is that convincing enough to consider changing out your existing light bulbs?  Still not sure?

YES, the 23 Watt CFL bulb is much more energy efficient than a 100 watt incandescent.

Forget the Calculations and Call Hovey Electric...We Help Companies Become More Energy Efficient

If your still confused about energy efficient technologies? Here is one of our articles that get's right back to the basics, check it out....

See my article "Watts" a Watt? If you want to see how to take this calculation further and calculate your energy savings from a new system upgrade...or...

Learn More About Energy Efficient Lighting

Hovey Electric has been installing lighting for over 32 years.  We are experts in energy efficient lighting solutions.  Even with all the information on the web, few people really understand what energy efficient lighting is all about.

We put together this eBook to help you better understand why energy efficient lighting may be beneficial to you or your business.  Check it out, It's FREE, No Obligation.....Just Good Information, Click on the Book Below. 

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