Solid-State Roadway Lighting Design Guide: Volume 1: Guidance (2020) / Chapter Skim
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Chapter 1 - Introduction
Chapter 1 - Introduction
Pages 1-7
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With greater and more precise control over optical distribution, the light levels of SSL luminaires beyond the calculation grid may be dramatically reduced, and the roadway design will still meet AASHTO criteria, although an element of safety might be missing. Therefore, research is needed to investigate the application of AASHTO criteria to SSL roadway lighting and, if the results dictate, provide guidance for changes or additions to those criteria.
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This white-SSL process occurs at a lower temperature than other light sources, which allows for a longer life for the light source as compared with gas or filament lights, as well as lower costs for dimming and color. LEDs also emit light from a very small area on the diode in a specific direction (as opposed to omnidirectional)
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The critical aspect of the two methods of generating light is that the phosphor-converted LED generally has a broad-spectrum output, whereas the HPS relies on the energy band conversion of electrons and has significant spectral gaps in the light output. Moreover, the SPD of LEDs can be tailored to achieve specific CCTs.
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HID sources are typically rated by the time in operation at which 50% of the lamps have failed, whereas LED sources are rated by the point at which lumen depreciation declines to 70% of the initial output. Some of these factors are quantified and included in LED test data acquired in accordance with Projecting Prior research, as well as the research Long Term Lumen Maintenance of LED Light Sources (IES TM-21-11)
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. Figure 3. TM-21 inputs for predicting lumen maintenance.
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Established methods of classifying photometric distribution (IES Types II, III, IV, and V and short, medium, and long) are not as relevant Because the standard distribution types with LED luminaires.
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• Photometric distribution can vary greatly with HID sources as well as among LED products. • The rated life of luminaires is based on different performance requirements.
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