Kouba-Cavallo Associates, Inc.
Lighting: An Energy Efficient Future


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Lighting has been one of the great success stories in energy efficiency of the last quarter of the 20th Century. And it could become another great success story of the next few years as we proceed further into the 21st Century.

During the years following the oil crises of the early 1970s, commercial building owners and managers reacted to high electricity prices by retrofitting offices, warehouses, and stores. First they turned to reducing unnecessarily overlit areas, and later they installed new lower wattage fluorescent tubes and electronic ballasts. As a result, energy use for lighting in the commercial sector fell even as the number of commercial buildings rose.

Now the success in the commercial sector may be a prelude to another great energy efficiency success--this time in the residential sector. The compact fluorescent bulb is the key that could unlock this success.

Like the fluorescent lamps found in commercial buildings, a compact fluorescent bulb is a tube. These tubes, however, are narrower and twisted around like a pretzel. Sometimes they are covered with a globe so that they look much like a standard incandescent bulb.

The big difference between compact fluorescents and their incandescent cousins is the amount of energy they use. Compact fluorescents use roughly one-quarter of the electricity that an incandescent bulb will use to give off the same amount of light. Of course the exact difference in light output will depend on how the tubes are shaped, whether it has a cosmetic globe, and a number of other minor things. But cutting the electricity use of a light by anywhere near 75% is a lot of savings. Below is a table of typical compact fluorescent bulbs and their equivalent incandescent bulbs.


7 watts
25 watts
15 watts
60 watts
18 watts
75 watts
27 watts
100 watts
32 watts
150 watts

Now the difference between a light using 60 watts and one using 15 watts may not inspire dreams about how you will spend all the money that you will save. But look around your house. You may see the light!

When I looked around my house, I realized that there are four places in my house where lights are generally on more than 3 hours each day: the kitchen, the living room (where we watch TV), the parlor (where the kids do their homework), and the porch. In the winter, the lights in these rooms are usually on much more than 3 hours each day. Moreover, with the exception of the porch, more than one bulb is burning in each of these rooms when they are being used.

You should know two other things about compact fluorescents. First, they cost a good deal more than incandescents. And then, they last much longer than incandescents. (If you think there's an economics problem coming up, you're right.)

Why should you care which lights stay on the longest in your house? Replacing all your incandescents with fluorescents would certainly reap large energy savings, but it would require a bit of an investment. Compact fluorescents usually cost between $5 and $15 per bulb. Since incandescents can often be purchased for 50 cents, that difference is quite significant. I can usually find compact fluorescents of high quality at my local hardware store for around $10. If you shop on the Web and are willing to buy 10 or more compact fluorescents at a time, you can purchase them on-line for as little as $6 per bulb. (Check out the links at the bottom of this page for on-line shopping sites.)

The upside to compact fluorescent bulbs' costs is that they last a very long time. The rated lifetime of most compact fluorescent bulbs is 10,000 hours. I twice tried to check this figure by turning on a light in my office and leaving it on. Both times that I tried this, however, I changed offices before the light burnt out. In contrast to the long lifetimes of compact fluorescent bulbs, incandescent bulbs are rated to last from 800 to 1,000 hours. It would take 10 or more incandescent bulbs to match the life of one compact fluorescent.

Now, let's add both types of bulbs' initial costs to their yearly energy costs and compare apples to apples. If you use a 60 watt incandescent light for a bit less than 3 hours each day, or 1,000 hours each year, and your local electric rate is 10 cents per kilowatt-hour, then the light is costing you $6 per year in electricity. Add 50 cents for a new bulb each year, and you have a total cost of $6.50 every year. A single compact fluorescent would initially cost you $10.00 for the bulb, but would only cost you $1.50 in electricity each year.

One might be tempted to say that 10 years of lighting will cost $65.00 for each 60 watt incandescent bulb and just $25.00 for each 15 watt equivalent compact fluorescent bulb, but that would ignore the notion of discounting future costs. To help you with the discounting calculation, we have created the little calculator below. All you need to do is replace the numbers that appear in the boxes with your own local information. For instance, if you live in the service territory of a utility that charges 13 cents per kilowatt-hour, you should replace the "10" in the first box with "13". If you have a lighting fixture that stays on for 6 hours each day and has five 60 watt incandescent bulbs, then you need to replace the "3" that is in the second box with "6", the "60" in the first box of the second table with "300", and the "15" in the second box of the second table with "75".

When you have filled in the information to your satisfaction, click on the "Compute" button below the tables.

Table 1
How much do you pay for electricity in cents per kilowatt-hour? (If you don't know, assume 10 cents/kilowatt-hour.)  
How many hours per day on average do you leave this bulb on each day? (If you are not sure, assume 3 hours.)  
What is the interest rate that you receive for your savings? (Many banks pay about 4 percent interest.)  

Table 2
Characteristic of the Bulb

Incandescent Bulbs

Compact Fluorescent Bulbs
Energy Usage of the bulb (in watts)


Expected life of bulb (in hours)


Cost of bulb



Now that you have compared the lifetime cost of continuing to use your incandescent bulbs to the cost of switching to compact fluorescent bulbs, you may wonder which lights to change out first. Certainly you want to replace the lights that are used for the greatest number of hours each day --not the lights that are in your closets or crawlspaces and are rarely turned on. Look around your house. You probably have the lights on in your kitchen and TV room the longest.

In any case, start experimenting with a few compact fluorescent bulbs so that you can find types that you like. The articles below have information about the various characteristics of lights --like color warmth, color rendering, glare, and more. What is important, though, is that you join the growing number of folks that are turning on to compact fluorescent bulbs and capturing the savings associated with the next energy efficiency success story --residential lighting.

Here are some links to more information on lighting and some places to purchase energy efficient bulbs and lamps.

An Enlightening Comparison from the Alliance to Save Energy

Information on energy efficient lighting and other home energy conservation opportunities from the American Council for an Energy Efficient Economy

Article - Consumer Guide: Energy Efficient Lighting for the Home

Article - Shedding Light on Home Lighting Use

Article - History in a New Light: The House of Seven Gables Lighting Retrofit

Article - Lighting Makeovers: The Best is Not Always the Brightest

Article - Bright Prospects for Lighting Retrofits

Article - Steps to Successful Lighting Programs

Philips Lighting Company, a supplier of compact fluorescents

Duro-Test Lighting, a supplier of compact fluorescents

GE Lighting, a supplier of compact fluorescents

Lights of America, a supplier of compact fluorescents

Osram Sylvania, Inc., a supplier of compact fluorescents

Real Goods, a supplier of compact fluorescents

Sunpark Electronics Corp., a supplier of compact fluorescents

ParaLite Electronic, a supplier of compact fluorescents

This list of suppliers is not complete. I regret leaving out any supplier. Please let me know of any web sites that I have missed and I will include them at the next update.

written by James Cavallo, associate editor at Home Energy Magazine
and principal at Kouba-Cavallo Associates, Inc., Downers Grove, Illinois.

For additional information, contact Jim Cavallo by sending e-mail to cavallo@Kouba-Cavallo.com.

This page was last updated on September 14, 2001.