| Throughout this web site, there are claims of saving XXX lbs of CO2 emissions and $XX in energy costs by using compact fluorescent light bulbs (CFLs) instead of regular (incandescent) light bulbs. While some people will just take our word for it, others will want to know how we came to those conclusions. This section details the formulas used in our calculations. Background
Before beginning any calculations or comparisons, it is important to understand some basic differences between CFLs and incandescent light bulbs, which are the watts of electricity used and the expected lifetime of each. Understanding these differences will help ensure that two equivalent light bulbs will be compared. The first difference between the two types of bulbs is that CFLs use up to 80% less electricity, or watts, to produce similar light output, or lumens, as incandescent bulbs. For example, a typical 100 watt incandescent light bulb will have a light output between 1600 and 1750 lumens, which is a similar range to that of a 23 watt CFL. This is why a 23 watt CFL would be labeled as a 100 watt replacement. It is important that two light bulbs that produce similar light output are being compared. Another difference is how long they last, or the life of the bulb. CFLs last anywhere between 7,000 and 12,000 hours compared to incandescents that will only last between 750 and 1,000 hours. In order to perform an accurate comparison, the calculations made for either type of bulb must be made based on using each bulb for the same number of hours. For example, it would be inaccurate to calculate the CO2 emissions generated by using an incandescent bulb for its 1000 hour life, then try and compare that to the CO2 emissions generated over the 10,000 hour life of a CFL. That would be like comparing the CO2 emissions generated by driving a non-hybrid car for 100 miles and driving a hybrid car for 200 miles, just because the hybrid gets twice the mileage as the non-hybrid. In order to perform an accurate comparison, both must be driven the same amount of miles, or in the case of the light bulbs, the same number of hours.
For our sample calculations we will be comparing a 100 watt incandescent light bulb to a 23 watt CFL, using both for 10,000 hours. Calculating CO2 emissions savings
First, the amount CO2 emissions generated by using each light bulb for 10,000 hours must be calculated. In order to do so, the electricty used by each over the 10,000 hours will have to be determined since it is the electricity that causes the actual CO2 emissions. Then the amount of CO2 emissions generated by using that amount of electricity can be determined. To figure out how much electricity each bulb will use over 10,000 hours, multiply the number of watts each bulb uses times 10,000 hours. CFL: 23 watts x 10,000 hours= 230,000 watt hours
incandescent: 100 watts x 10,000 hours= 1,000,000 watt hours Electricity is typically measured in kilowatt hours (kWh). To convert from watt hours to kWh, we must divide the watt hours calculated above by 1,000: CFL: 230,000 watt hours / 1,000 = 230 kWh
incandescent: 1,000,000 watt hours / 1,000 = 1,000 kWh Now that the kWh of electricity each light bulb will use has been calculated, the amount of CO2 emissions that electricty will generate can be determined. This is done by multiplying the kWh calculated above by 1.34 (a single kWh of electricity will generate 1.34 lbs of CO2 emissions - US Energy Information Administration): CFL: 230 x 1.34 = 308.2 lbs of CO2 emissions
incandescent: 1,000 x 1.34 = 1,340 lbs of CO2 emissions
Based on the above calculations, a 100 watt incandescent bulb will generate 1,032 lbs MORE CO2 emissions than an equivalent CFL. Calculating energy cost savings
We need two things to calculate how much it costs to light a lightbulb over 10,000 hours: total kWh of electricity used and cost per kWh. We already calculated the kWh of electricty needed for the 100 watt incandescent (1,000 kWh) and the 23 watt CFL (230 kWh), so now all we need is the cost per kWh. The number we use is $.12 per kWh. This can vary greatly depending on where you live. For example, according to the US Department of Energy, in October 2006, the average cost in the New England States was $.16/kWh, in the Mid-Atlantic states it was $.13/kWh, and in West North Central states it was $.8/kWh. In order to get an accurate number, you should read your most recent electric bill. For this exercise, we'll use $.12/kWh: CFL: 230 x $.12 = $27.60
incandescent: 1,000 x $.12 = $120.00
Now that we have the cost to light both bulbs for 10,000 hours, subtracting the two gives us a cost savings of $92.40 by using a 23 watt CFL instead of a 100 watt incandescent bulb. Please note: The purchase price of the bulb was not factored into energy cost savings. The typical 100 watt incandescent bulb will last 1,000 hours, therefore, 10 bulbs would have to be purchased to last as long as one 10,000 hour CFL. However, since a single CFL is about the same price as replacing 10 incandescent bulbs, we chose not to factor price into energy cost savings.
For questions about any of our calculations, don't hesitate to contact us at: info@thebulb.com |
