Comparison of Fluorescent Lamps
Types of Ballasts
Ballast Performance Characteristics

The vast majority of interior lighting for small business is provided with linear fluorescent fixtures and lamps. Fluorescent lamps are usually about three to four times more efficient than incandescent lamps and can last eight to twenty times longer. Tubular fluorescent lamps have much lower maintenance costs than incandescent or compact fluorescent lamps. The "T' designation for fluorescent lamps stands for the tubular shape of the lamp. The number after the "T" gives the diameter of the lamp in eighths of an inch.

Typical linear fluorescent lamps are compared in the table below.

Early fluorescent lamps were sometimes criticized as not producing enough warm colors, making them appear too white or uncomplimentary to skin tones. Color rendering of fluorescent lamps is very important. Modern, efficient fluorescent lamps use rare-earth phosphors to provide good color rendition. The Color Rendering Index (CRI) describes how a light source affects the appearance of a standardized set of colored patches under standard conditions. A cool white fluorescent has a CRI of 62. But today there are lamps available with CRIs of 80 and above that simulate natural daylighting and incandescent light. The minimum acceptable CRI for most indoor applications is 70, but levels above 80 are recommended. T8 and T5 lamps are available only with high-quality phosphors that provide CRIs greater than 80.

T8s offer better efficiency, lumen maintenance, color quality, fixture optics, and lifecycle costs than T12 systems. T5 lamps and ballasts have some efficiency and optical advantages over T8s, however T5 lamps cannot replace T12 or T8 lamps because of differences in physical and electrical characteristics. T5 lamps come in different lengths than T8 and T12 lamps. Smaller, brighter and using less energy than the T8, the T5 is becoming popular in Europe and finding increasing use in the U. S. for new construction. The disadvantages of T5 lamps are cost and glare. The price of T5 lamps is two to three times higher than that of T8 lamps. Glare can be prevented, though, by choosing luminaires that shield the light sources from view.

Types of Ballasts
Fluorescent lights require ballasts. Ballasts are devices that provide the proper voltage and current to fluorescent lamps, which do not regulate themselves like incandescent lamps. There are three basic types of ballasts: magnetic, hybrid, and electronic.

Magnetic Ballasts contain a magnetic core of several laminated steel plates wrapped with copper windings. Magnetic ballasts are the least expensive and the least efficient of all ballasts. Magnetic ballasts have greater power losses than electronic ballasts. Magnetic ballasts are available with dimming capability; however, they cannot be dimmed below 20 % and still use more electricity than electronic ballasts. Almost all of the four-foot T12 lamps in the market today are operated by magnetic ballasts.

Hybrid Ballasts use a magnetic core-and-coil transformer and an electronic switch for the electrode heating circuit. After they start the lamp, the hybrid ballast disconnects the electrode-heating circuit. Hybrid ballasts cost more than magnetic ballasts, but are more energy efficient than magnetic ballasts.

Electronic Ballasts are the most expensive, but they're also the most efficient. Operating lamps with electronic ballasts reduces electricity use by 10% to 15% over magnetic ballasts for the same light output. They're also quieter, lighter, and they virtually eliminate lamp flicker. There are a variety of electronic ballasts available for use with fluorescent lamps. Instant-start electronic ballasts are slightly more efficient than rapid-start ballasts, but result in some degradation of lamp life. Rapid-start operation is usually required for reduced-output ballasts and dimming ballasts. Dimming ballasts allow the light level to be controlled between 1% and 100%. In the present market, almost all of the T8 lamps are operated by electronic ballasts. In 2000, DOE issued a new ballast standard that will require high-efficiency electronic ballasts in all new commercial fixtures manufactured after April 1, 2006, and electronic ballasts for most replacement applications after July 1, 2010.

Ballast Performance Characteristics
When comparing ballasts, it is important to understand the following performance characteristics: ballast factor (BF), ballast efficacy factor (BEF), and system efficacy.

Ballast Factor (BF) is the ratio of light output of a lamp or lamps operated by a specific ballast to the light output of the same lamp(s) operated by a reference ballast. It can be used to calculate the actual light output of a specific lamp-ballast combination. BF is typically different for each lamp type. For electronic ballasts, the BF can range from about 0.7 to 1.5. It usually makes sense to specify a BF between 0.85 and 1.0 to maximize light output from a specific lamp/ballast combination without overdriving the lamps, which can shorten lamp life.

Ballast Efficacy Factor (BEF) is the ratio of ballast factor (as a percentage) to power (in watts). BEF is useful in comparing ballasts within a given type of lighting system, for example, for the class of 4-foot fluorescent lamps.

System Efficacy is the ratio of light output to the power, measured in lumens per watt (LPW), for a particular lamp ballast system.

You can contact your local lighting contractor to perform a detailed lighting analysis for you. Note: All linear fluorescent fixtures need to be hard wired by an electrician.

Sources: US DOE Office of Energy Efficiency and Renewable Energy, US DOE FEMP "Greening Guidelines," Lighting Research Center