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T5 and T5 high output (T5 HO) fluorescent lamps are increasingly popular members of the RESEARCH RECAP Yukio Akashi Lighting Research Center linear fluorescent family since entering the US market in 1995. They have sparked the imaginations of designers, luminaire manufacturers and researchers alike. They are being aggressively marketed and innovatively designed into new compact luminaires. But in spite of these efforts, many of us are left wondering whether we should consider using T5 luminaires instead of T8 luminaires. There is some heavy debate about whether they are better than other fluorescent lamps. In this column, therefore, we’ll tackle the question Figure 1. The relative light output variation as a function of ambient temperature for T5 and T8 fluorescent lamps. (This diagram is based on SILHOUETTE T5, T5HO & T5 Circular Fluorescent Lamp Technology Guide, Philips Lighting Company) of whether T5 systems are indeed more efficacious than T8s. Are T5 systems really more efficacious than T8s There really seem to be no significant differences in efficacy among T5, T5 HO, and T8 systems (Akashi, 2002). To more fully answer this question, we should consider several important factors: Ambient temperature and lamp efficacy: Lamp manufacturers usually show slightly higher Are T5s Better Than T8s TTable 1. Lamp efficacy and lamp-ballast efficacy for T5, T5 HO, and T8 lamps. Lamp Efficacy Lamp-Ballast System Efficacy Manufacturer A Manufacturer B Initial Lamp Light Input Input Lamp Power Temp Output Efficacy Power Ballast Efficacy Power Ballast Efficacy Type (W) (°C) (lm) (lm/W) (W) Factor (lm/W) (W) Factor (lm/W) F28T5 28 F54T5HO 54 F32T8 32 25 2,610 93 63 0.90 75 62 1.00 84 35 2,900 104 63 0.90 83 64 1.00 94 25 4,400 81 117 1.00 75 117 1.00 75 35 5,000 93 117 1.00 85 117 1.00 85 25 2,950 92 59 0.88 88 59 0.90 90 35 2,714 85 59 0.88 81 59 0.90 83 efficacy values for T5 and T5 HO lamps than for T8 lamps in their catalogs because manufacturers usually provide light output data at their optimal ambient temperature for each lamp type: 25°C (77°F) for T8 lamps and 35°C (95°F) for T5 lamps. Figure 1 shows the performance of T5 and T8 lamps as a function of ambient temperature. As you can see, there is roughly a 10 percent difference in light output for both T5 and T8 lamps between 25°C and 35°C. The difference in optimal temperature between T5 and T8 lamps could affect lamp performance in different luminaires. In closed luminaires where temperatures tend to be high, T5 lamps might perform better than T8 lamps but in open luminaires, T8 lamps might perform better than T5 lamps. But, you might ask, what are the actual temperatures in luminaires The LRC measured temperatures in luminaires using T5 HO and T8 lamps (Gu et al., 2002). The temperatures in open, direct/indirect pendant luminaires ranged from 29°C to 36°C, while the temperatures in closed, direct recessed luminaires ranged from 38°C to 46°C regardless of lamp type. If you compare these temperatures with Figure 1, you can see that in the open luminaires, T5 lamps will tend to emit less light than under their optimal condition of 35°C. In the closed luminaires, where the temperatures are much higher than 35°C, T5 lamps might function better than T8 lamps. Ballast loss: Ballast loss is yet another important factor. Table 1 compares several lamp-ballast system efficacies for T5, T5 HO, and T8 systems. Although the system efficacy varies among manufacturers, its value at the optimal temperature for each of the three systems (25ºC for the T8 systems and 35ºC for the T5 systems) does not appear so different from each other. Since ballast performance varies widely, large ballast losses might cancel any increases in lamp efficacy (Gu et al., 2002). Luminaire efficiency: The 10°C difference in optimal temperature between T5 and other fluorescent lamps causes another problem about luminaire efficiency 1 . American National Standards Institute/ Illuminating Engineering Society of North America (ANSI/IESNA) standards require an ambient temperature of 25°C for photometry. The bare T5 lamps might be operated at an ambient temperature of 25°C while the ambient temperature in a luminaire could be much higher than 25°C. The higher temperature in the luminaire could make the T5 lamps emit more light. This procedure could lead to luminaire efficiency values greater than 100 percent! Until these issues are worked out by the 1 Luminaire efficiency is determined by dividing the lumen output of the bare lamps used in a luminaire by the lumen output from the luminaire itself. 6 LD+A/January 2003 www.iesna.org
appropriate standards-setting organizations, specifiers should be careful in interpreting luminaire efficiencies for luminaires with T5 and T5 HO lamps. So, which is more efficacious: T5 HO luminaires and T8 luminaires To directly compare T5 HO luminaire performance with T8 luminaire performance, the LRC asked an independent testing laboratory to measure the light output of eight typical luminaires. During the measurements the room temperature was maintained at 25°C. Table 2 summarizes the results. The measurements suggest that the system efficacies of T5 HO luminaires are practically identical to those of T8s in the same luminaire type. (T5 systems might be more efficacious than T5 HO and T8 systems, but we have not compared both these systems yet.) Should we consider using T5 systems After all this discussion, you might be left with the question of whether you should still use T5s. I would still suggest using T5 systems, as long as they meet your budget and requirements. Although T5 systems still cost more than other fluorescent lighting systems, their price will decrease if demand increases and more such systems are manufactured, as appears to be the case. Why should we use T5 systems T5 and T5 HO lamps are the most environment-friendly lamps among the linear fluorescent family. It is unquestionable that T5 and T5 HO lamps have less impact on the global environment than T8 or T12 lamps. Their smaller diameter results in less bulb glass, phosphor material, mercury content, and packaging materials and leads to thinner luminaire housings and therefore less installation expense. Are there other advantages of T5s over T8s The small diameter of T5 and T5 HO lamps gives them high optical controllability. Their line-source quality might allow for a compact optical design, accurately and efficiently delivering light to where it is needed. Such an advantage might allow more elegant or crisp luminaire designs and therefore build better impressions of T5 systems. However, note that, if you use smaller optics with T5 lamps than optics with T8 lamps, the optical efficiency of T5 systems might not necessarily be significantly higher than that of T8 luminaires. How can T5 and T5 HO luminaires be used Bulb luminances of T5 and T5 HO lamps are higher than other fluorescent lamps. A T5 lamp and a T5 HO lamp have 3 and 1.8 times higher luminances than a T8 lamp, respectively (Akashi, 2002). The high luminances of these lamps can cause glare if the lamps are improperly used. They are quite suitable for direct/indirect lighting. If, however, you use T5 and T5 HO lamps with indirect pendant luminaires in an office room, the room could look darker than the work plane illuminance implies. This is because there are no visible light sources that usually give you cues to estimate how much light is coming from the luminaires. In such a case, indirect luminaires with thin slits cut through the side panel and the Table 2. Measured light output data Luminaire Measured data Light Luminaire Type Lamp Optics Input (W) output efficacy (lm) (lm/W) Indirect 3xT8 None 83.4 5892 70.6 pendant (open) 2xT5HO None 121.6 8552 70.3 Direct/indirect 3xT8 Louver 90.3 6153 68.1 pendant (open) 2xT5HO Louver 121.3 8390 69.2 Direct recessed 1xT8 Louver 27 1349 50.0 luminaire (closed) 1xT5HO Louver 52.8 2655 50.3 1xT8 Flat diffuser 26.9 1260 46.8 1xT5HO Flat diffuser 53.1 2640 49.7 www.iesna.org
Page 1 and 2: Lighting Design + Application Janua
Page 3 and 4: President Randy Reid Past President
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Page 13 and 14: Section News continued from previou
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Page 25 and 26: POKEMON PANDEMONIUM Alex Sebeshalmi
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