Technologies > T5 AND T5HO FLUORESCENT LAMPS
Description: T5 and T5HO lamps, often referred to generically together as T5 lamps, represent less than 10 percent of the total lamp market, but they are very popular in lighting fixtures such as linear indirect, direct/indirect, recessed baskets, soffits, valences, cove, wall-mount and low-bay fixtures.
Characteristics: A T5 lamp is a 5/8-inch diameter lamp, about 40 percent smaller than T12 lamps. The thinner lamps enable better photo-optic control of the light produced by the fixture, increasing efficiency and providing uniform distribution of its light output.
T5 and T5HO lamps are built to metric dimensions, which means they can’t be used to retrofit T8 or T12 fixtures. The four-foot T5 or T5HO is 45.8 inches from end to end, a little shorter than T8 and T12 lamps. T5 and T5HO lamps are therefore purchased in fixtures specially designed for their use. Otherwise, they can be used anywhere T8 and T12 lamps are currently used—although T5HO lamps are not recommended for applications where their higher brightness can be viewed directly and cause visual discomfort.
A 28W T5 produces about the same light output as a 32W T8 and a 54W T5HO produces close to twice the light output of T8 and T12 lamps when these lamps are operated as part of a ballasted lighting system. The nominal light output of a four-foot 54W T5HO lamp is 5,000 lumens, compared to 2,900 lumens for a 28W T5 lamp and 2,850 lumens for a 32W T8.
As a result of the same or greater light being produced from a smaller area, T5 lamps appear brighter and of course so do T5HO lamps. T5HO lamps are not recommended for fixtures where the light source is directly visible. They are too bright. However, this characteristic makes them ideal for compact indirect fixtures.
Note that initial rated light output for T5 and T5HO lamps is based on peak output at an ambient temperature of 35 ºC (95 ºF), whereas T8, T12 and circular T5 lamps are based on 25 ºC (77 ºF). This is because lamp manufacturer assume that T5 and T5HO lamps are going to be used in more compact fixtures, where it’s assumed that greater heat-up would occur during operation.
In addition, T5 lamps contain a very small amount of mercury (3mg), offer high lumen maintenance (about 93-95% at 8,000 hours), have good color rendering (82 CRI), and are available in an expanding range of color temperatures, including 3000K, 3500K, 4100K, 5000K, 6000K and 6500K.
Finally, T5 and T5HO lamps provided a rated life of 20,000 hours compared to 24,000 hours for a T8 lamp.
Electrical Characteristics: T5 lamps are available in 14W, 21W, 28W and 35W in nominal linear lengths of two, three, four and five feet respectively, and in 22W and 40W circular shapes. Among the linear sizes, the four-foot 28W is most common.
T5HO lamps are available in 24W, 39W, 54W and 80W in nominal linear lengths of two, three, four and five feet respectively, and in a 55W circular shape. The four-foot 54W lamp is most common.
Table 1. Comparison of nominal four-foot lamp types. Source: OSRAM SYLVANIA
*28W T5, 54W T5HO and 32W T8 light output values are for 3000K, 3500K and 4100K lamps, not 5000K, 6000K or 6500K, which will generally be slightly less.
In review, efficacy is a measure used to compare the relative efficiency of different lamps and lighting systems, expressed as lumens of light output per watt of electrical input. We can compare the nominal efficacy of lamps, which is somewhat useful, all the way to the maintained efficacy of lamp-ballast systems, which many consider most useful since it most reflects typical operation after installation.
A 28W T5 lamp is more efficacious than a 32W T8 lamp (104 LPW for the T5 vs. 94 LPW for the T8). This T5 lamp-ballast system also operates at a higher maintained system efficacy than a comparable T8 lamp-ballast system (96 LPW at 8,000 hours of operation for the T5 system vs. 89 LPW at 8,000 hours of operation for the T8 system).
T5HO initial lamp and maintained system efficacy is somewhat less than that for T8 lamps and lamp-ballast systems.
One of the interesting things about the T5 lamp is that it is the first linear fluorescent lamp designed specifically to operate exclusively on electronic ballasts. T5 and T5HO lamps work best with programmed-start ballasts, which are designed to optimize lamp life. Universal-voltage (120-277V and 347-480V) ballasts, dimming ballasts, and ballasts that can drive up to four lamps are available.
T5, T5HO, T18 and T12 ballasts are not compatible because the lamps operate on different currents. Even T5 and T5HO lamps can’t be used with the same ballast.
T5 and T5HO ballast technologies are trending towards higher case temperatures and expanded voltage range (to 480V), and the lighting systems themselves are increasingly being used with occupancy sensors, controls and switching applications.
Applications: Due to their unique combination of strengths and weaknesses, T5 and T5HO lamps are ideally suited for some applications but not others. These lamps’ limitations, coupled with a higher cost than T8 lamps and ballasts, have resulted in modest penetration into the lamp market.
About 10 years ago, T12 lamps held about 95 percent of the linear fluorescent market and T8 lamps had made a small penetration of about five percent, while T5 lamps weren’t even on the radar, according to lamp manufacturer OSRAM SYLVANIA. Today, according to NEMA, T12 lamps now make up about 65 percent while T8 lamps have 33 percent and T5 and T5HO lamps now comprise the remaining two percent.
While overall penetration has been low during these lamps’ first eight years in the North American lighting market, they have become very popular for certain applications where their slim profile and high brightness are strengths, most notably linear suspended indirect and low-bay industrial fixtures but also recessed baskets, soffits, valences, cove and wall-mount fixtures.
Indirect Lighting: With their high intensity, T5-lamped indirect and direct/indirect pendants can be mounted as much as 12 to 15 ft. apart on ceilings as low as nine feet (although some manufacturers say they can go lower). In contrast, T8 fixtures generally should be mounted 10 to 12 ft. apart on ceilings at least 9.5 ft. high, which is higher than many office ceilings. With fixtures that have optics designed specifically for T5 lamps, a uniform light pattern is produced on the ceiling.
In addition, T5HO lamps, which produce 5,000 lumens in the 54W 4-ft. model, have resulted in already slim T5 indirect fixtures becoming even slimmer by allowing them to use one lamp instead of two. This not only improves the fixture aesthetically and makes it less architecturally and visually obtrusive, but also improves application flexibility (by allowing indirect lighting into more spaces). The use of T5HO lamps may also result in the need for fewer fixtures in the design, resulting in cost savings.
High-bay Lighting: T5HO lamps have been incorporated into high-bay fixtures as an energy-saving alternative to HID fixtures.
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