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Publication #FCS3270

Energy Efficient Homes: Fluorescent Lighting1

Hyun-Jeong Lee, Kathleen C. Ruppert, and Wendell A. Porter2

Quick Facts

• Compact fluorescent lamps/bulbs, commonly referred to as CFLs, cost less than regular incandescent lighting in three ways.

  1. CFLs consume significantly less energy than incandescent bulbs. To produce the same brightness, an ENERGY STAR® qualified CFL uses only about ¼ of the energy that an incandescent bulb uses.

  2. By using ENERGY STAR® qualified CFLs, you'll save on air conditioning costs because they generate ¾ less heat than regular incandescent bulbs.

  3. A CFL lasts up to 10 times longer than an incandescent bulb. This means fewer bulbs to purchase and fewer trips to the store, saving you both the time and the travel costs you would normally spend on replacing burned-out incandescent bulbs.

• Replacing incandescent bulbs with CFLs in the rooms where you spend the most time, like your family room, living room, and kitchen, will result in tangible dollar savings and comfort.

• Fluorescent lighting is no longer the industrial lighting of yesteryear—for example, it is now available in varieties to suit almost any need from ambient mood lighting to crisp task lighting.

Terms to Help You Get Started

  • ballast: The device that stabilizes the electric current for stable operation of a bulb. Depending on the bulb, it can either be attached to the bulb (generally as in compact fluorescent bulbs) or be a part of the fixture (as with pin-based and fluorescent tubes). Units with separate ballasts and bulbs are preferable because ballasts last much longer than bulbs.

  • bulb, lamp vs. fixture: Lamp is the industry term for what we commonly refer to as a light bulb, whereas a fixture is the housing unit that connects the bulb (lamp) to a power source.

  • CCT (Color Correlated Temperature): A measurement of the appearance in tone of any given light source, i.e., how “warm” or “cool” it is, with “warm” being closer to the yellow/orange end of the color spectrum, and “cool” being closer to the bluish end. Measured in Kelvin (K) temperatures.

  • CRI (Color Rendering Index): A measurement of how accurately the emitted light renders the color of illuminated objects.

  • CFL (Compact Fluorescent Lamp): A fluorescent tube of small diameter wound into a coil, spiral, or typical incandescent bulb shape so that it is comparable in size and shape to conventional incandescent light bulbs.

  • efficacy: See Lumens per watt (LPW).

  • fluorescent: Light source that, when electrical current is applied, glows because of a chain of events initiated by the current's arc.

  • hardwired (dedicated) systems: These systems consist of a ballast and fluorescent bulb socket permanently wired into a fixture by the manufacturer, or as part of a retrofit kit.

  • incandescent: Light source that glows because of its filament being heated to a high temperature.

  • integral light: Bulbs that combine a bulb, ballast, and standard screw base in a single sealed assembly, which must be discarded when the bulb burns out. They can be installed in any standard screw-type light fixture where incandescent bulbs are normally used.

  • Kelvin (K): A measurement for the characteristics of visible light in determining color temperature, often used for categorizing CCT.

  • kilowatt-hour (kWh): Used on utility bills to define a unit of energy usage, e.g. a 100-watt light bulb (0.1 kW) used for 10 hours (0.1 kW x 10h) consumes 1 kilowatt-hour of energy during that time.

  • lumens: Units of measurement for brightness issued by a light source, e.g. a candle generates about 13 lumens while a 100-watt incandescent bulb generates about 1,750 lumens.

  • lumens per watt (LPW): An indicator of a bulb's efficiency determined by dividing the number of lumens generated (as indicated on the packaging by the bulb manufacturer) by its wattage; the higher the LPW, the greater the efficiency. Sometimes referred to as efficacy.

  • mercury: A metallic element used in small amounts in CFLs and fluorescent tubes that requires special handling because of its behavior when exposed to air.

  • modular units: This type of unit has a separate two- or four-pin base bulb that plugs into a separate adapter or ballast. When the bulb burns out, a relatively inexpensive replacement bulb can be installed in the original ballast and pin base.

  • reflector bulbs: Perfect for providing directional light, as with recessed lights in kitchens or ceiling fans. There are outdoor reflector bulbs as well that are generally much larger than the reflectors designed for use inside. The outdoor types are sealed to withstand the weather and generally should not be used with timers, photocells, and motion sensors unless otherwise specified on the package.

  • watt: A unit of electrical power/power consumption.

How much would I save by switching to compact fluorescent bulbs?

Let's compare an incandescent bulb and a CFL with the same light output. A 60-watt bulb does not necessarily provide more illumination than a 15-watt bulb. Why? Because watts measure energy use while lumens measure light output. Lumen information appears on bulb packaging. For example, a 60-watt incandescent bulb produces about 800 lumens. You can replace this 60-watt incandescent bulb with a 15-watt CFL and get the same amount of lumens (light output), but the CFL will use 45 watts less energy (U.S. Department of Energy, n.d.a.). See Table 1 to compare estimated purchase price and residential energy costs of incandescent versus fluorescents, each with the same light output (lumens).

Is it true that fluorescent lighting is harsher than incandescent?

This is not necessarily true. Two factors, the Color Rendering Index (CRI) and Color Correlated Temperature (CCT, sometimes called K), affect a light's harshness. Fluorescent lighting is generally more uniform than other light sources.

What is the Color Rendering Index (CRI)?

CRI measures the perceived color of objects under artificial light on a scale of 0 to 100. The higher the number, the more natural and vibrant an object will appear. Incandescent bulbs usually have CRI values of 100. Old-style fluorescents had values of 62, at best, which is why people used to complain that fluorescents gave false colors. A CFL with a CRI of 80 or more is suitable for everyday residential use.

What is the Color Correlated Temperature (CCT)?

CCT is a measurement of the appearance of the light source itself, how “warm” or “cool” it seems. It is measured in Kelvin Temperature from 0 to 10,000+ and expressed as (K). Oddly, the lower the Kelvin number is, the warmer (more yellow) the light color. As the number goes up, the bluer the light source will be. For instance, a CCT of a standard incandescent bulb can range from 2800K to 3100K, which provides warm, white lights. A fluorescent with a CCT of 3000K will provide the same warm, white light that an incandescent bulb produces. A 3500K fluorescent bulb gives about the same light as a halogen. Some bulb manufacturers promote 5000K to 6000K, which produces cooler (bluer), white light, as a daylight bulb.

What should I look for when purchasing bulbs?


Compare brands for price, lumens per watt (LPW) and hours of life. To calculate lumens per watt, divide the lumens by the watts. For instance, an 800-lumen 60-watt incandescent bulb would have a LPW of approximately 13 (800 divided by 60); an 800-lumen 15-watt CFL would have a LPW of about 53 (800 divided by 15). Remember, the higher the LPW, the greater the efficiency and the more light you receive for the energy used.

As a result of changes in the Appliance Labeling Rule, comparing light bulbs is now much easier (Federal Register, 2010). The label on the front of the package must include brightness (lumens) and estimated annual energy cost of using the bulb 3 hours per day at a rate of 11 cents per kWh. A "lighting facts" label, as seen in Figure 1, must also be on the side or back of the package. This label must include information on brightness (lumens), energy cost, bulb life, color temperature (CCT), wattage and, in some cases, voltage and mercury information.

Figure 1. 

Sample ENERGY STAR® qualified CFL label.


[Click thumbnail to enlarge.]


On newer packaging, you will be able to locate the "light appearance" or CCT information on the "lighting facts" label. See Figure 1 as an example. On older packaging, compare CRI and Kelvin Temperature (CCT) if displayed on the product package—CRI will be a 2-digit number and Kelvin will be a 4-digit number with K, for example, 3500K. For an idea of how a room will look in varying shades of white light (warm–yellow or cool–blue), see the ENERGY STAR® Choose a Light Guide at

Instructions for Appropriate Use

When you purchase a bulb, check its packaging for any restrictions on use. For example, some bulbs should not be used in enclosed fixtures and some may specify that the base be up or down. Many are for specific fixtures, such as recessed cans, dimmer switches or outdoor fixtures. Bulbs used incorrectly can cause fire and/or electric shock. This pertains to incandescent bulbs as well, such as using a 100-watt bulb in a fixture that calls for 40 watts.

Can I use dimmers or 3-way switches with fluorescent lights?

Yes, but you need to find the right bulbs. Manufacturers produce CFLs that will work in standard incandescent fixtures with dimmers or 3-way switches, but using the wrong kind can be dangerous and costly if the bulb fails. Read package directions carefully to pick the right CFL for your purpose. Incorrectly installed bulbs can cause fires.

What's different about an ENERGY STAR® qualified CFL?

A CFL must meet specific criteria to earn the ENERGY STAR® qualified label (ENERGY STAR®, May 7, 2008). These criteria include very specific requirements for efficacy (LPW), CRI, CCT, product packaging, and warranty provisions. Some highlights include the following:

  • Requirement for maximum mercury content (less than 5 milligrams)

  • Third-party testing requirement

  • Stringent CRI requirements

  • High-heat testing requirements for CFLs with reflectors

The ENERGY STAR® website has links to a wealth of information to help you select and purchase CFLs (ENERGY STAR®, n.d.a.).

What's different about ENERGY STAR® qualified lighting fixtures?

Light fixtures that have earned the ENERGY STAR® label combine quality and attractive design with high levels of energy efficiency. Compared with traditional or standard fixtures, qualified fixtures (ENERGY STAR®, n.d.b.):

  • Use one-fourth the energy;

  • Last at least 10,000 hours (about seven years of regular use);

  • Distribute light more efficiently and evenly;

  • Come in hundreds of decorative styles, including portable fixtures (like desk lamps, for example) and hard-wired options such as front porch, dining room, kitchen ceiling and under-cabinet lighting, wall sconces, bathroom vanity fixtures, etc.;

  • Deliver convenient features such as dimming capability on some indoor models (fixture must have a dimming ballast to be dimmable), and automatic daylight shut-off and motion sensors on some outdoor models; and

  • Carry a two-year warranty, which is double the industry standard.

Should I turn off the fluorescent lights when I leave the room to save more?

Contrary to popular belief, turning off fluorescent lights really does save energy. Frequent switching may shorten bulb life, but electric bill savings will more than compensate for the shorter lifespan, especially if you end up using more fluorescents than incandescents. The U.S. Department of Energy (n.d.b.) recommends using fluorescent bulbs in fixtures that you tend to use for at least 15 minutes at a time or several hours a day for the most savings. See the publication, When To Turn Off Your Lights (, for specific recommendations.

I've heard that CFLs (like other fluorescent tubes) contain mercury—how do I dispose of them? What if I accidentally break one?

As a general rule of thumb, CFLs require special handling, so don't throw them away with the regular household trash. While CFLs can be recycled, they should not be thrown into your recycle bin either. Check or, call 1-800-CLEAN-UP, or contact your local waste-management agency for proper disposal guidelines in your community.

For current information on what to do and what not to do when a CFL is broken, refer to this website: Note that this same website also contains links to information on proper disposal.

By using CFLs, you can reduce power demand that will help reduce mercury emissions from power plants. Mercury emissions in the air come from both natural and manufactured sources. Coal-fired power plants are the largest contributors because the naturally occurring mercury in the coal is released into the air when coal is burned to make electricity. In fact, coal-fired power generation is responsible for over 50% of the mercury emissions in the United States (ENERGY STAR®, November 2010). While fluorescent bulbs do contain very small amounts of mercury—an average of 4 milligrams compared to older thermometers containing about 500 milligrams—it is sealed within the glass tubing and is not released when the CFL is intact or in use. Moreover, with proper handling, mercury in the CFLs can be recaptured through recycling.

What else is new regarding light bulbs?

As a result of the Energy Independence and Security Act of 2007, effective January 1, 2012, regular light bulbs have to be more energy efficient (U.S. Environmental Protection Agency Backgrounder, Spring 2011). For example, the standard 100-watt regular screw-in light bulb has to use 27% less energy or 72 watts of energy or less rather than 100 watts. By January 2013, the 75-watt bulb will have to use 53 watts or less energy. By January 2014, the 60-watt bulb will have to use 43 watts or less and the 40-watt bulb will have to use 29 watts or less energy.

References and Resources

ENERGY STAR®. (May 7, 2008). ENERGY STAR® program requirements for CFLs – Partner Commitments. Retrieved May 31, 2012, from

ENERGY STAR®. (November 2010). Frequently asked questions: Information on compact fluorescent light bulbs (CFLs) and Mercury, November 2010. Retrieved May 31, 2012, from

ENERGY STAR®. (n.d.a). Light bulbs for consumers. Retrieved May 31, 2012, from

ENERGY STAR®. (n.d.b). Residential light fixtures for consumers. Retrieved May 31, 2012, from

Federal Register. (July 19, 2010). Appliance Labeling Rule, 16 CFR Part 305. Retrieved June 1, 2012, from

Federal Trade Commission. (June 14, 2011). FTC Materials will help shoppers understand new light bulb labels coming in 2012. Retrieved June 1, 2012, from

Miller, C., Sullivan, J., and Ahrentzen, S. (2012). Energy Efficient Building Construction in Florida. ISBN 978-0-9852487-0-3. University of Florida, Gainesville, FL.

U.S. Department of Energy. (n.d.a). How energy-efficient light bulbs compare with traditional incandescents. Retrieved May 31, 2012, from

U.S. Department of Energy (n.d.b). Energy Savers – When to turn off your lights. Retrieved May 31, 2012, from

U.S. Environmental Protection Agency Backgrounder. (Spring 2011). Energy independence and security act of 2007 (EISA) frequently asked questions. Retrieved June 1, 2012, from


Table 1. 

Estimated Cost to Household Comparison: Incandescent Bulbs and Fluorescent Bulbs

Light Output


Bulb Type & Energy Use

Bulb Purchasing CostA

Rate Life


Energy Cost

for 10,000 hours

(at $0.10/kWh)

Total Cost

for 10,000 hours

(Bulb + Energy)


Incandescent: 60 watts





Fluorescent: 15 watts






Incandescent: 75 watts





Fluorescent: 20 watts






Incandescent: 100 watts





Fluorescent: 25 watts





AEstimated purchasing costs do not include taxes, shipping, handling fees, recycling fees, or travel expenses associated with acquisition of bulbs at point of purchase, nor do they include additional taxes, fees, or charges required by your utility provider.

Note: Actual light output, bulb cost, and rated life may vary by product. Utility rates vary by provider.



This document is FCS3270, one of an Energy Efficient Homes series of the Department of Family, Youth and Community Sciences, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. This material was initially prepared in June 2008 with the support of the Department of Environmental Protection, Florida Energy Office, which is now the Office of Energy, Florida Department of Agriculture and Consumer Services. This revised version was prepared June 2012 with the support of the Florida Energy Systems Consortium ( Any opinions, findings, conclusions, or recommendations expressed herein are those of the author(s) and do not necessarily express the views of the sponsoring organizations. Visit the EDIS website at


Hyun-Jeong Lee, former assistant professor, Department of Family, Youth and Community Sciences; Kathleen C. Ruppert, extension scientist, Program for Resource Efficient Communities; and Wendell A. Porter, lecturer and P.E., Department of Agricultural and Biological Engineering; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.