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eflector might help increase the apparent brightness of the room. Or, you can add sparkle! Using sconces can increase the brightness impression of a space, too (Akashi, 2000; Akashi, et al., 2000). T5 and T5 HO lamps can also be used for high-bay applications, where high intensity discharge (HID) lamps are usually used. The high location of the luminaires But in spite of these efforts, many of us are left wondering whether we should consider using T5 luminaires instead of T8 luminaires decreases the apparent size of the high intensity light sources and therefore might reduce glare caused by those light sources. If T5 and T5 HO lamps are used with appropriate luminaires, they have several advantages over HID systems such as dimming capability, better color rendering, longer life, better lumen maintenance, instant restrike capability, and shorter warm up times than HID systems. efficacy to T8s, you can think of T5 systems as better alternatives of T8 lamps because T5 systems are very environmentally friendly. To better understand T5 and T5 HO lamp performance, more objective evaluation should be conducted on ambient temperature and ballast performance. The optical and physical design of T5 luminaires could probably also be improved to optimize the temperature, and therefore, the light output. More demonstrations of T5 lamps with direct/indirect pendant luminaires for office applications and direct luminaires for high-bay applications are needed to show the benefits of T5 systems. The pages of LD+A are a good place to publish them. Through such demonstrations, T5 luminaire design will be improved. For instance, the slit luminance of T5 direct luminaires can be optimized so that the slits can provide cues to enhance brightness impression. The luminance of the luminous surfaces of direct T5 luminaires for high-bay applications can be optimized to reduce discomfort glare. My guess is that T5s are here to stay, and their future is a bright one! Reference Akashi, Y. 2002. “Lighting Answers: T5 Fluorescent Systems.” Troy, NY: National Lighting Product Information Program, Lighting Research Center, Rensselaer Polytechnic Institute. Akashi, Y., Tanabe, Y., Akashi, I., Mukai, K., 2000. “Effect of sparkling luminous elements on the brightness impression,” Lighting Research and Technology, 32, 1, pp.19-26. Akashi, Y., 2000. “Gloom is doomed,” LD+A, May 2000, pp.88- 93. Gu, Y., Akashi, Y., Lou, X. Narendran, N., O’Rourke, C. 2002. “Performance characteristics of T5 fluorescent lamps,” Proceedings, Illuminating Engineering Society of North America, 2002 Conference, pp. 135-142. What is next As I mentioned above, T5 systems do not surpass T8s in terms of efficacy. Since, nonetheless, T5 systems still have a comparable 8 LD+A/January 2003 www.iesna.org
Glare is the sensation produced by luminances within the visual field that are sufficiently greater than adaptation luminance, which result in annoyance, discomfort, loss of visual performance and visibility. The IESNA recognizes two types of glare. Discomfort glare results in irritation, while disability glare can be more serious, interfering with visual performance or visibility. Glare models are mathematical equations that have been developed from psychophysical data. These models predict subjectively experienced glare as a function of the following: 1) Luminance of the glare source 2) Luminance of the field of view (background or adaptation luminance) 3) Solid angle subtended by the glare source at the eye (visual size) 4) Position of the glare source in the field of view All the models predict that glare will increase as a function of source luminance, size, and proximity of the glare source to the direction of view. Similarly, all the models predict that glare will decrease as adaptation luminance increases. Five prominent models have been developed to predict glare as a function of the same environmental parameters: 1) Visual Comfort Probability 2) British Glare Index 3) Glare Limiting System 4) Nordic Glare Index Method 5) CIE Unified Glare Rating (UGR) While these models all use the same four parameters to define the effect of a glare source, each incorporates other more subtle differences. Specifically, the different models vary the coefficients and exponents that are applied to these factors, they apply different mathematical operations to multiple glare sources, and they differ in whether or not the glare source itself is included in the field of view. The IESNA currently uses the Visual Comfort Probability (VCP) system. VCP represents the probability that a normal observer will not experience discomfort when viewing a lighting system under defined conditions. The development of www.iesna.org VCP was initiated after the Second World War by Luckiesh and Guth who were inspired by then-new fluorescent technology to investigate the single and combined effects on human perception and performance of source luminance, size, background and field luminance, and the position of the glare source within the visual field. The current VCP procedure published in The IESNA Is VCP the right quality metric for Discomfort Glare LIGHTING FOR QUALITY Lighting Handbook is the result of nearly a half-century of work by numerous investigators. The IESNA Lighting Handbook is very clear about the limitations of VCP. The Handbook notes: “This system was tested and validated using lensed direct fluorescent systems only. VCP should not be applied to very small sources such as incandescent, and high intensity discharge luminaires, to very large sources such as ceiling and indirect systems, or to non-uniform sources such as parabolic reflectors.” Many lighting designs no longer involve the use of lensed direct fluorescent sources, and so VCP calculations should not be applied to the majority of sources used in current lighting practice. Consequently, it could be argued that the IESNA does not have a discomfort glare evaluation system, or at best has a system that is valid for a very small percentage of new designs. There is a natural design requirement to minimize glare, so we are left with the question of whether an alternate evaluation system can be identified that designers can use to predict and thereby control or eliminate glare. The Unified Glare Rating system has been developed by the International Commission on Illumination (CIE) committee TC 3-13, as an attempt to combine the best features of the major discomfort glare evaluation systems in terms of practicability and familiarity with results of glare prediction. The formula results in UGR values on a scale ranging from about 10 to 30 for typical applications. Higher values indicate more discomfort glare. In 2002, the CIE published a document entitled “CIE Collection on Glare,” which claims that the UGR can be applied to the following sources: 1) Small sources defined as having a projected area smaller than 0.005 m 2 (approx. 8 in 2 ) 2) Large sources, such as luminous ceilings and indirect lighting 3) Large sources with a transition region between normal sources and the luminous ceiling 4) Non-uniform indirect lighting 5) Complex sources such as low brightness specular sources with louvers The UGR might therefore be valid for application to many more lighting installations than VCP. An article by Mistrick comparing VCP and UGR was published in the summer 1999 edition of the Journal of the Illuminating Engineering Society of North America. This article compared and contrasted the results of glare calculations applied to a variety of lensed direct and parabolic troffers. Mistrick concluded that application of the two different models produced similar results (correlation of .68 between the ratings produced by the two different models). The correlation was not perfect because the two methods differ with respect to how they characterize different aspects of the glare stimulus. For example, UGR contains larger exponents to characterize the effects of source luminance and position. In the VCP system, adaptation luminance includes the contribution of the luminaires, while this is not the case with the UGR system. Should the IESNA replace VCP Clarence E. Waters, Ph.D., P.E. Dale K. Tiller, Ph.D.
Page 1 and 2: Lighting Design + Application Janua
Page 3 and 4: President Randy Reid Past President
Page 5 and 6: Control device manufacturers have i
Page 7: appropriate standards-setting organ
Page 11 and 12: notes on lighting design • New Se
Page 13 and 14: Section News continued from previou
Page 15 and 16: Teens Pave Way for Energy-Efficient
Page 17 and 18: Commercial projects often present u
Page 19 and 20: Given the current cost-cutting time
Page 21 and 22: DALI IS HERE TO STAY New hardware a
Page 23 and 24: 2002 INTERNATIONAL ILLUMINATION DES
Page 25 and 26: POKEMON PANDEMONIUM Alex Sebeshalmi
Page 27 and 28: (above and right) At Rockefeller Ce
Page 29 and 30: Table 2—LEED Program Categories,
Page 31 and 32: Table 4. Comparison of New York And
Page 33 and 34: Architectural Lighting Design, 2nd
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