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1、LSD 25-2008 A NEMA Lighting Systems Division Document Best Practices for Metal Halide Lighting Systems, Plus Questions and Answers about Lamp Ruptures in Metal Halide Lighting Systems Prepared by Lamp and Luminaire Sections National Electrical Manufacturers Association 1300 North 17th Street, Suite
2、1752 Rosslyn, Virginia 22209 www.nema.org LSD 12 and LSD 12AFirst Published December 10, 2000 LSD 12 and 12A Combined into LSD 25May 23, 2002 LSD 25 Last RevisedAugust 05, 2008 The requirements or guidelines presented in this document, a NEMA Lighting Systems Division white paper, are considered tec
3、hnically sound at the time they are approved for publication. They are not a substitute for a product sellers or users own judgment with respect to the particular product discussed, and NEMA does not undertake to guarantee the performance of any individual manufacturers products by virtue of this do
4、cument or guide. Thus, NEMA expressly disclaims any responsibility for damages arising from the use, application, or reliance by others on the information contained in these white papers, standards, or guidelines. LSD 25-2008 2008 Copyright 2008 by the National Electrical Manufacturers Association.
5、ii Contents Section Page 1 Introduction1 2 Objective of This Paper .2 3 Metal Halide Lamp Design Basics 2 4 Metal Halide Arc Tube Failure Mechanisms and Lamp Rupture3 5 Metal Halide Lamp Classifications3 6 Change in the 2005 National Electrical Code4 7 Essential Practices for Minimizing Risks from M
6、etal Halide Lamp Rupture.4 8 Metal Halide Lighting System Luminaire Options & Trade-Offs.5 9 Practices for Minimizing Risk from Metal Halide Systems6 10 Summary of Commonly Available Metal Halide Systems8 11 Conclusion.9 12 Questions and Answers about Lamp Ruptures in Metal Halide Lighting Systems.9
7、 LSD 25-2008 2008 Copyright 2008 by the National Electrical Manufacturers Association. 1 Best Practices for Metal Halide Lighting Systems 1 Introduction Metal halide lighting systems represent one of the great innovations in lighting applications. Todays systems provide the ability to deliver a vari
8、ety of light levels, from low to very high output, with high-energy efficiency, long life, and excellent color. In addition, since metal halide lamps are compact sources, these systems offer the ability to direct and focus light in a manner not possible with more diffuse high efficiency light source
9、s, such as fluorescent lamps. Metal halide systems remain the preferred technology for many commercial and industrial applications and, for some, such as sports lighting, virtually the only practical option. Metal halides ability to deliver the “white light” increasingly preferred in many applicatio
10、ns has made it the high-pressure discharge system of choice, and this trend has resulted in the overwhelming success of these systems in the marketplace. NEMA estimates that there are close to 40 million metal halide systems installed in North America alone, with the vast majority being in commercia
11、l and industrial applications where system efficiency, good color rendering, and life cycle economy are important. Since metal halide lamps operate at elevated internal pressures compared with most other general-purpose light sources, manufacturers have historically provided explicit instructions on
12、 their proper use. In addition, manufacturers provide warning information that is designed to reinforce the need to follow these instructions, since failure to do so can significantly increase the risk of a lamp rupture. A lamp rupture can eject hot particles into the luminaire and, if the luminaire
13、 does not completely enclose and contain the hot particles, into the surrounding space. If hot particles land on combustible materials, there is a risk of fire. Despite the large number of metal halide lamps used (over 100 million in the last ten years), there are very few reported instances of prop
14、erty damage claims resulting from the rupture of metal halide lamps. When even this small risk of rupture is not acceptable, enclosed luminaires should be used, or where enclosed luminaires are undesirable, Type-O lamps should be used. The 2005 National Electrical Code (NEC) affects the options avai
15、lable for some installations. NEMA manufacturers have the goal to reduce risk as much as possible without unreasonably sacrificing product utility by continually striving to improve the application and use of metal halide systems. LSD 25-2008 2008 Copyright 2008 by the National Electrical Manufactur
16、ers Association. 2 2 Objective of This Paper The objective of this paper is to provide educational information for the selection, operation, and maintenance of metal halide lighting systems with specific emphasis on those items pertinent to the risks associated with lamp rupture. The implications of
17、 the 2005 NEC provisions on these risks are addressed. 3 Metal Halide Lamp Design Basics The metal halide lamp is designed around a sealed tube with an electrode in each end (and sometimes with an extra “starting electrode” at one of the ends). See Figure 1. This assembly of a quartz or ceramic tube
18、 and electrodes is commonly called the arc tube. The arc tube is mounted to a metal frame, sealed within a glass outer bulb, and fitted with a base to form a lamp. See Figure 2. Starting Electrode Main ElectrodeMain Electrode Pinch or Other Type Of Seal Structure Figure 1. Arc Tube Support Outer Bul
19、b Arc Tube Support Base (These are representative illustrations. There are many more types.) Figure 2. Metal Halide Lamp LSD 25-2008 2008 Copyright 2008 by the National Electrical Manufacturers Association. 3 The metal halide arc tube contains a starting gas (typically argon or xenon), mercury, and
20、metal halide salts. The salts most used today consist of iodides of the metals sodium, scandium, and dysprosium. Metal halide arc tubes typically operate at higher temperatures and pressures than mercury vapor arc tubes. Mercury vapor arc tubes operate typically at temperatures of 600- 800 C and wit
21、h contained pressures of 3-5 atmospheres. Metal halide arc tubes operate typically at temperatures of 900-1100 C and with contained atmospheric pressures of 5-30 atmospheres. 4 Metal Halide Arc Tube Failure Mechanisms and Lamp Rupture Virtually all metal halide lamps reach end of life in a benign ma
22、nner. However, because of the high internal operating pressure of the arc tube, there is the potential for an arc tube rupture. With only a glass outer envelope surrounding the arc tube, the outer envelope may be breached by particles from an arc tube rupture. If this occurs, hot particles may be ej
23、ected from the lamp. The small, but existing, possibility of a rupture is why most, if not all, lamp manufacturers provide strongly worded warning statements with metal halide lamps. Chemical reaction of the arc tube wall material with the metal halides may, over time, weaken areas of the arc tube s
24、ufficiently that it may fail due to a crack or excessive thinning. If this happens during the heating and cooling that occurs when the lamp is cycled, the result is typically a lamp that extinguishes and does not re-ignite. If this failure occurs when the arc tube is at full wattage and pressure, th
25、e tube may shatter. 5 Metal Halide Lamp Classifications Every metal halide lamp is classified by the lamp manufacturer as to the recommended manner in which it should be used. The following are the three American National Standards Institute (ANSI) classifications:1 1. Lamps classified as Type-E are
26、 to be used only in suitably rated enclosed luminaires, in accordance with UL 1598 and CSA C22.2 No. 250.0.2 2. Lamps classified as Type-S have historically been used in both open and enclosed luminaires. Their use in open luminaires is restricted to operation in the vertical position. This category
27、 is limited to certain lamps in a 360- to 1000-watt range. A change in the 1 ANSI C78.380, Annex B, American National Standard for Electric LampsHigh Intensity Discharge Lamps, Methods of Designation, American National Standards Institute, New York. 2 UL 1598, Luminaires, Underwriters Laboratories I
28、nc., Northbrook, IL. CSA C22.2 No. 250.0-00, Luminaires, CSA International, Toronto, Canada. NMX-J-324-ANCE, Association of Standardization and Certification, Mexico. Note that these three standards are the Tri-national Luminaire Safety Standard. LSD 25-2008 2008 Copyright 2008 by the National Elect
29、rical Manufacturers Association. 4 2005 NEC eliminated the option of using Type-S lamps in open luminaires in those installations regulated by the NEC. 3. Lamps classified as Type-O may be used in open or enclosed luminaires. Type-O lamps comply with ANSI Standard C78.3893 for containment testing. 6
30、 Change in the 2005 National Electrical Code The 2005 NEC4 requires luminaires that use metal halide lamps (except for thick-glass PAR lamps) to be either enclosed or to have some physical means to ensure that only Type-O lamps can be used in them. This means that, in practice, open luminaires will
31、utilize a special lamp holder that will accept only Type-O lamps. (Type-O lamps have either a slightly different lamp base (mogul) or bulb neck diameter (medium) than typical Type-E and Type-S lamps.) Since Type-E lamps should only be used in enclosed luminaires, the intent of this change in the NEC
32、 is to ensure the use of Type-O lamps in open luminaires for those installations under the jurisdiction of the 2005 NEC. This change in the NEC reflects experience with the newer technology Type-O lamps in actual installations. This experience is that, even in those rare instances when an arc tube r
33、uptures, the Type-O lamp construction is effective in preventing the rupture particles from penetrating the outer bulb, thus preventing hot particles from falling into the surrounding space. This increased security does not in any way diminish the safety record of the Type-S lamps. 7 Essential Pract
34、ices for Minimizing Risks from Metal Halide Lamp Rupture To significantly reduce the risk of lamp rupture, the lamp manufacturers warnings and operating instructions must be followed. Furthermore, all NEMA lamp manufacturers strongly recommend that lamps be group replaced at or before their rated li
35、fe. NEMA lamp manufacturers require that some types of metal halide lamps be turned off at least once a week for a minimum of 15 minutes to reduce the possibility of rupture in continuously operating installations. However, they no longer require that Type-O lamps be turned off once a week for a min
36、imum of 15 minutes in continuously operating installations since Type-O lamps incorporate an integral self-shielding technology designed to minimize any ejection of hot particles from the lamp. While not required, some manufacturers note that cycling can be employed as an additional measure if possi
37、ble failure of the lamp containment mechanism would be considered unacceptable in a given installation. 3 ANSI C78.389 American National Standard for Electric LampsHigh Intensity Discharge Methods of Measuring Characteristics, National Electrical Manufacturers Association, Rosslyn, Va. 4 2005 NEC, A
38、rticle 410.73 (F) (5). LSD 25-2008 2008 Copyright 2008 by the National Electrical Manufacturers Association. 5 8 Metal Halide Lighting System Luminaire Options & Trade-Offs Metal halide luminaires are available for myriad applications including retail stores, commercial office space, manufacturing p
39、lants, warehouses, sports lighting, and roadways. Each of these applications has very different light distribution and control needs. It is primarily the job of the luminaire to take the light produced by the light source and to distribute it within the application space. To satisfy the diverse rang
40、e of performance and economic criteria that exist, a wide variety of luminaire designs, with differing optical configurations and capabilities, have been developed. For instance, many manufacturing facilities have high ceilings. Industrial high bay luminaires have been developed to provide narrow ph
41、otometric distributions that control glare within the normal field-of-view of those occupying the space. Luminaire reflectors with open bottoms or reflectors with simple flat lenses/enclosures are often applied in such applications. Luminaires for use in spaces with lower mounting heights, such as m
42、any commercial retail stores, can produce excessive visual glare in the normal field-of-view if they were supplied either without lenses or with flat glass lenses. For these lower mounting heights, “low bay” luminaires are frequently designed with prismatic lenses. These lenses serve to optically re
43、direct the light produced from the luminaire into a broad, even pattern within the space and also reduce the brightness of the luminaire to a level that is visually comfortable for the occupants of the spaces. Lower wattage metal halide lamps are often used in luminaires for commercial spaces, inclu
44、ding down-lights, adjustable accent units, and track lighting. While some of these luminaires incorporate a lens, some architectural applications demand luminaires with specific optical and/or thermal performance characteristics that would be adversely impacted by inclusion of a lens. Accordingly, T
45、ype-O lamps are typically employed. PAR lamps, which have integral reflectors and thick glass envelopes, are also used where the lamp is relied upon to provide optical control. Many luminaires are offered with the option of including special lamp holders that allow a Type-O lamp to be used, but prev
46、ent a Type-E or Type-S lamp from being successfully installed in the luminaire. Such constructions are standard for those open luminaire installations that comply with the 2005 NEC. There are reasons, driven by application needs, to offer both open and enclosed luminaires. Users should assess the co
47、nsequences of a possible ruptured arc tube (and broken outer bulb) when choosing a lighting system. Relative to Type-S lamps in open luminaires, both enclosed luminaires and Type-O lamps in open luminaires offer more protection in the event of arc tube rupture. It is therefore important to include r
48、isk management as a selection criterion. It is not practical to simply dictate that all luminaires be one type or the other. LSD 25-2008 2008 Copyright 2008 by the National Electrical Manufacturers Association. 6 The following factors need to be considered in any choice of system components: Desired
49、 maintained light level Light distribution pattern Number of luminaires required Efficiency of the system Initial acquisition and installation costs Cost of operating the system- electricity Cost and ease of maintenance- cleaning luminaires, changing lamps Probable conditions at the site once in use Level of acceptable risk from a ruptured arc tube Specifier requirements Aesthetics The final decision by any end user typically is a combined consideration of all factors. 9 Practices for Minimizing Risk from Metal Halide Systems The following practices s