Wisconsin Energy Efficiency and Renewable Energy Resource

Fluorescent Lamps

The fluorescent lamp was another invention that Thomas Edison provided the world in 1896. Today, the fluorescent lamp comes is many sizes and styles, from compact fluorescent lamps to linear fluorescent lamps. Some of the newer technologies such as T-5 and T-8 fluorescent lamps are the most energy-efficient lamps available today and have overcome many of the issues related to cold weather operation. Some models available today are dimmable with the use of special ballasts. Fluorescent lamps are named by the bulb size in eighths of inches. For example, the most common fluorescent lamp size is a T-12 which is 12 eighths of an inch or 1-1/2" in diameter. The discussion will be limited to fluorescent lamps most useful to agriculture: compact fluorescent lamps, T-12 and T-8. T-5 lamps are suitable for office space but give off too much heat to be used in sealed fixtures so they will not be discussed.

Compact Fluorescent Lamps (CFL)

CFLs are one of the most significant developments in lighting in recent history, combining the efficiency of a fluorescent lamp and the convenience of an incandescent bulb. When introduced in the mid-1980s, the ballasts were large and wouldn't fit many fixtures designed for incandescent bulbs. In the last few years, the ballasts have been reduced in size so they are only slightly larger than an incandescent bulb and new types have been introduced that have more compact fluorescent tubes and diffusing covers to hide the fluorescent bulb so esthetically they can be used in more places. CFLs use 75% less electricity than an incandescent bulb with the same light output. The most recent models introduced have minimum starting temperature as low as -20°F which makes them useable for many outdoor applications provided they are protected from moisture. These lamps do provide light output instantly but require a few minutes to get to full output. Warm up time will vary with the ambient temperature; colder temperatures require a longer warm up period. The standard CFL should not be used in livestock housing unless it is installed in a sealed fixture such as a jelly jar (see photo at right). There are some manufacturers that have developed water resistant CFL fixtures for use specifically in livestock housing. Compact fluorescent lamps have a lamp life of 6000 to 10,000 hours, 6 to 13 times longer than an incandescent bulb and are available in incandescent equivalent sizes from 15 to 200 watts and higher.

T-12 Fluorescent Lamps

This is the old standby that has been used for many years. They are very efficient lamps compared to incandescent lamps but have a disadvantage for farm use because they have decreased light output and flicker below 50°F unless one uses the less energy-efficient high-output version which will work to -20°F. T-8 fluorescent lamps should be used for new installations. If the proper fixture has been used (water-proof for animal housing or wet locations like a milk house) it can be converted to T-8 lamps by replacing the lamps and ballast. The lamp sockets are the same for T-12 and T-8 lamps. If T-12HO (high output) lamps are being used in an indoor application which will likely not get below 0°F, then the lamp could be converted to a standard T-8 lamp by replacing the lamp sockets along with the lamps and ballasts. This will save more than 50% in lighting operational costs.

T-8 Fluorescent Lamps

T-8 lamps are a relatively new type of fluorescent that have the highest efficiency of any lamp types used in an agricultural environment. The fixtures for T-8 lamps look similar to the commonly used T-12 lamps except the bulbs are 1" in diameter instead of 1-1/2". A T-8 lamp provides about 15% more lumens per watt and the electronic ballasts are 40% more efficient than electro-magnetic ballasts of T-12 lamps. Some standard T-8 ballasts can start in temperatures as cold as 0ºF compared to 50ºF, allowing T-8 lamps to be used in cold applications. The T-8 lamp uses an electronic ballast which operates at high frequency, thus eliminating the annoying flicker associated with T-12 electro-magnetic ballast when ambient air temperatures are cooler than 50°F. If the correct fixtures are being used (water-proof for animal housing or wet locations like a milk house, see photo at right), a T-12 fixture can be converted to use T-8 lamps by replacing the lamps and ballast. The same lamp sockets are used for both T-8 and T-12 lamps. If T-12HO (high output) lamps are being used in an indoor application which will likely not get below 0°F, then the fixture could be converted to a standard T-8 lamp by replacing the lamp sockets along with the lamps and ballasts. If the same lighting level as T-12HO lamps is desired, then high-output T-8 ballast and lamps with recessed double contacts (F17d type ends) would need to be used or additional fixtures added. The average life of a T-8 lamp is 20,000 hours, 65% longer than T-12 lamps, which reduces maintenance costs.

If you have information you think would be useful to this site please contact
Scott Sanford, Senior Outreach Specialist, University of Wisconsin, sasanford@wisc.edu.