Consulting-Specifying Engineer - May 2008 - (Page 26) On the lighting horizon Everyone always wants to know about the Next Big Thing. Whether it’s for personal gain (like the best stock options) or for professional development, we’re always clamoring to know what the latest and greatest technology will be. Here are two: LED lights LEDs are beginning to be considered for some niche general lighting applications. Low light-level requirements are most primed for consideration including step lighting, night lighting, accent downlighting, architectural/entertainment lighting where color is the driver, and emerging outdoor site lighting applications. The biggest barrier in these emerging markets is high initial cost until the volume or industry players make it more competitive to current available and proven source technologies. Based on some of the new products scheduled to be on display at Lightfair International, Las Vegas. LEDs are on the market with designers in mind. They’re classy and trendy at the same time, and their performance levels are becoming attractive. Specific locales have different codes for LEDs, however, so they’re not completely standard across the board. They’re also unfamiliar to electrical inspectors, so even if you’ve specified everything right, the inspector may not fully understand the system. According to Robb Allen, AIA, IES, president and director of technical services at Clear Stream Studio, Green Bay, Wis., the future of solid-state lighting holds exciting potential if/when major technological and economic challenges are met head-on. • Efficacy improvements in lumens per watt are improving dramatically for bright white LEDs to compete with other sources, but lag far behind in warmer color temperatures important in many architectural applications. • While the visible light from the LED is cooler than many other sources, a massive amount of heat is produced on the “backside,” or chip side, of the LED. This heat currently requires roughly a 2-in. cube of aluminum heat sink to dissipate the heat generated from just a single, 1 W LED. You can imagine the size, scale, and cost related to producing a general illumination luminaire that would require dozens to hundreds of these LEDs to produce the lumens required to meet most commercial applications. • Lamp life originally touted at 100,000 hours, now in general is promoted at 50,000 hours and is driven totally by the actual thermal conditions at a critical location within the chip, which is totally dependant on the design of the luminaire and the ambient environment temperature range where it’s installed. Digital lighting controls There’s a movement toward going digital and/or wireless with controls, mostly because of the savings. It eliminates conduit/pipe, which can save 35% of the overall electrical construction costs because copper, steel, and a lot of labor are reduced. Everything is low-voltage and is controlled by DALI, or Digital Addressable Lighting Interface, a protocol set out in IEC 60929 or many other widely available commercial low-voltage control systems and electronic ballasts. Due to the fact that the entire lighting system is highly customizable, the potential is ripe for miscommunication or unrealistic expectations at an affordable price. Commissioning is the only way to ensure that a system like this works properly. And initial set-up can be time-intensive due to software programming issues that are only beginning to be simplified without calling in the “Tech Squad.” Once it works, however, it works well, and maintenance is often simple programming changes. daylight, especially if photosensors aren’t incorporated into the lighting design. One half of the classroom may be over-lighted if overhead lights don’t turn off when sunlight pours in a window. And the intensity of direct sunlight can create hot spots and wreak havoc with the HVAC system. This is especially common for older large clear or diffuse glazed large ceiling skylights, which often create intense daylight in a small area on the classroom floor and emit large amounts of radiant (heat) energy into the space. In most cases, air conditioning is forced to compensate for poor daylighting control, offsetting any energy savings that might have been gained by including daylighting in a design, or worse yet, increasing energy use. Smaller skylights as well as skylights that track and/or diffuse the sun’s rays, especially those that control light distribution throughout a room and whose lighting levels can be controlled by the teacher, may be the best bet. Most daylighting industry design references recommend and national energy codes limit skylight area (square foot) to floor area (square foot) ratios to 3% to 5%. Most computer modeling illustrates this to be the best balance in providing appropriate energy saving daylight without creating a net negative effect by overtaxing heating and air conditioning systems using current available technology. Some areas of the country offer utilitydriven incentive rebates for reducing electrical energy consumption, so incorporating skylights into a design can save the school even further. School buildings are open during peak energy usage hours, so if you design for less energy use, you’re saving the school district even more money, speeding up the payback on relatively costly upfront investments like skylights. Remembering that schools are long-term, 20- to 50-year investments, design professionals and school board members need to reinforce with the public during referendum time 26 Consulting-Specifying Engineer • MAY 2008
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