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7 Early LEDs were designed to the old ratio of red:yel- · Replacement approach results: low:green of 1:4.6:2 based on circa 1933 standards developed No replacement program: 35%; based on glass lens. The new 2005 ITE LED performance Complaint-driven: 35%; specification changes the ratio to 1:2.5:1.3, which was based Routine, scheduled replacement: 24%; on human factors issues. Replacement on vendor product life cycle: 3%; and Based on in-service test results: 3%. While LED measurement issues are largely beyond the · Results for scheduled replacement: scope of this synthesis, some mention of the complexities is Greater than 6 years: 52%; worth noting. LED clusters are unique light sources differing Five years: 38%; and greatly from incandescent lamps in physical size, luminous Six years: 10%. flux (the measure of the perceived power of light), spectrum · Fifty-five percent prefer national guidelines (not stan- (colors), and spatial distribution (LED clusters are not point dards) for minimum light output with 60% preferring to sources like incandescent lamps). Temperature of measure- adhere to the guidelines based on agency-established ment also affects the result; therefore, LED measurement procedures. results differ considerably in various laboratories. LEDs' · Seventy-eight percent have inadequate or no funding unique characteristics therefore require new methods. The for monitoring/replacement programs. Commission Internationale De L'Eclairage (CIE), a standards body involved in the development of standards for measuring The following is a summary of the main points ascer- the optical properties of LEDs, has been recommending new tained from the survey: definitions and new measurement conditions to reduce dis- crepancies. However, the standards have not kept up with · Current usage of LED signal modules is prevalent and LED technology as it continues to evolve. The net result is growing. difficulty in assessing LED performance in the field. There is · Many agencies are now approaching the life span of also an expectation that CIE will come up with a new edition their initial installations. of CIE 127-1997, which is the foundation of LED measure- · Most use a 5-year warranty, but scheduled replace- ments (5). However, CIE 127-1997 did not cover sufficiently ment tends to be on a greater than 6-year cycle; there- the measurement of total luminous flux and color of LEDs, fore, there is a growing likelihood of old LED signal which are very important in traffic signal applications. modules in the field with light output that is below specification. · Most have no routine replacement program or they are ITE SURVEY driven by complaints (complaints are less likely with LEDs as they gradually dim over time). In 2006, the ITE conducted a survey of public agencies and · Although use of the 2005 ITE LED specification is vendors/manufacturers of LEDs. There were 75 responses strong, the minimum values for light output are of little from public agencies and 6 from vendors. The complete results use without routine monitoring/replacement programs. of the survey are included in Appendices A and B. The fol- · Most do not have adequate funding for monitoring/ lowing is a summary of the principal findings: replacement of LED signal modules. · 59% of respondents indicated that more than 50% of RESULTS OF FOLLOW-UP DISCUSSIONS their signal modules are LEDs. WITH AGENCIES FROM ITE · 82% use or plan to use the ITE LED specification. · The majority (73%) use a 5-year warranty period (10% do Many of the follow-up discussions with agencies confirmed not specify a warranty). the basic issues discussed previously. The following adds · Total failure rate (dark face) of LED modules is low some additional comments. (less than 5%) and is decreasing as product quality improves. · Indiana DOT has programmed replacement on a · 33% do not use a qualified products list. 6-year replacement schedule, subject to refinement as · 85% do no compliance testing. their experience base with the newer LEDs adds to · 60% have no monitoring/replacement procedure. their understanding. At this time, they do not plan to · Half use the specification for minimum light output; replace yellow LEDs on a 6-year cycle. They also plan half use no specification for minimum light output. aerial inspection and cleaning on a three-year cycle. · The number of responses dropped considerably on all At this time, they do not anticipate monitoring LED questions related to agency practices/procedures for performance. monitoring and replacement. This is possibly an indica- · Texas DOT has had issues with transients. They have tion of the number of agencies with no replacement pro- not been able to specifically pinpoint the cause. The gram and is consistent with survey results. problems appear to be less with new designs. Texas
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8 DOT reviews LED designs and does failure testing as One manufacturer met this specification with a photo- part of their acceptance testing process. cell on red, yellow, and green balls. The manufacturer · Louisiana DOTD had historically required a special has stopped making this LED due to Energy Star require- circuit in their LEDs that monitored light output. ments for wattage. Louisiana DOTD is concerned that At 85% ITE minimum output, the circuit caused the the lack of output monitoring can lead to an unsafe LED to go dark and a breaker to create an open circuit. condition.