Signs of the Times - October 2012 - (Page 38)

LED UPDATE ducts’ brightness factors continue to be misused and misunderstood. Consequently, it’s wise to establish a rating standard for lamp brightness, or at least provide a maximum rating that ensures the parameter doesn’t exceed certain values. People seldom look directly at lightsources. However, if the source is visible from common locations, it should not appear excessively bright, because such light can distort a viewer’s vision and harm their eyes. One should never stare into bright small, discrete, flat, bright and mechanically durable, modern LEDs are suitable for signage, display and directional lighting in proximity illumination situations. Interestingly, these same characteristics make them less desirable for high-quality, large-space, and broad-direction illumination. Individual LED lamps are relatively small and bright and, as efficacy improves, they will only get brighter at the unit level. Also, when contrasted against OLEDs, unit or discrete “Overt brightness is not always better for general or sign illumination and shouldn’t be considered a merit unless specified.” lights. This not only distorts viewers’ vision, it may harm their eyes (sometimes permanently if viewing duration is extensive). Fortunately, our eyes quickly close when we accidentally encounter ordinary, but excessively bright, lightsources. So what’s excessively bright? The lighting industry has implicit brightness-measurement standards, and most lighting designers know when a light source is too bright, or not bright enough. Generally, brightness requirements depend on the source distance from typical viewers and, of course, the expected, ambient brightness level. Additionally, because most lamps and luminaires are used indoors throughout the day, and outdoors during dark hours, the ambient light levels fit the low to medium range. The luminance or brightness levels of such luminaires should be 200 to 330 nits, which is a comfortable range for most viewers. LED strengths and challenges Lighting quality is often described only by color properties, but lumen distribution and brightness levels are also vital to quality, safety and energy efficiency. Because they are LEDs will remain flat for inorganic materials for the foreseeable future. Tiling LEDs to create expanded lamp surfaces is only practical if appreciable gaps remain between the individual lamps, but such spacing isn’t always effective for creating broad and uniform illumination. Dark spots on the lamp plane will generate uneven illuminance over the lighted surface. Increasing individual LED’s luminance beyond a certain level isn’t a cure, because increasing the current to produce more light will also produce glare and shorten the LEDs’ lifespan. LED improvement roadmaps High-quality illumination can be created from artificial light sources when it includes high CRI properties, appropriate CCT, luminance and light distribution. Combined, these facets help viewers perceive objects and color in a natural and comfortable manner. As LED technology invades such applications as outdoor lighting, downlighting and general space lighting, developers should consider designs that address luminance and light-distribution requirements. Such solutions aren’t necessarily straight- forward because deviating from present designs may adversely affect lamps’ thermal-management aspects and manufacturing costs. Further, as the technology matures, the costs should lessen, but possibly not enough to contend with other lighting technologies, especially if that group also advances its specific design applications. Various manufacturers advertise LED replacement lamps for linear, fluorescent, street and parking-lot lamps. However, independent laboratory evaluations reveal LED replacements underperform compared to linear-fluorescent lamps (LFLs), although, some evaluators say LEDs sometimes compare to, and even outperform, incumbent outdoor street lamps. Additional characterization may reveal that such results do not include glare factors. In addition, older fluorescent technologies and designs remain in use with outdoor high-pressure-sodium (HPS) and metal-halide (MH) lamps, which poses an unfair disadvantage in lamp-comparison studies. Depending on the parking lot size and optimal spacing plans for streetlights, both HPS and MH lamp and luminaire engineers could redesign for higher system efficacy. Such designs, however, may require increased lamp surfaces, which could make them more hazardous, because breakage probability might increase with resulting mercury spillage. LEDs have a clear advantage in such applications because they are rugged and contain no mercury. Nevertheless, LED replacement lamps for wide-area illumination need to improve further so they can produce higher-quality lighting with less glare, and higher overall luminous efficacy at lower costs. LED luminaire designers and manufacturers can achieve such improvements with innovative technologies, and more elaborate measurements for light distribution and luminance mapping for design verification. n 38 SIGNS OF THE TIMES / OCTOBER 2012 / www.signweb.com http://www.signweb.com

Table of Contents for the Digital Edition of Signs of the Times - October 2012

Sign of theTimes - October 2012
ST Update
Technology Update
Vinyl Apps
Strictly Electric
LED Update
Software Update
Technology Review
Technology Review
Sign Museum News
New Products
2012 Vehicle Graphics Contest
Entry-level Electronic Digital Signage
The Proposed ISA Reorganization Plan
Enter ST's 2013 Intl. Sign Contest
SGIA Expo 2012
The Value of Signs
Advertising Index
Editorially Speaking

Signs of the Times - October 2012