ASHRAE Journal - February 2010 - 78

Solid-State Lighting, Part 2: Applications By Matthew Wiggins, Ph.D.; Kurtis McKenney; John Dieckmann, Member ASHRAE; and James Brodrick, Ph.D., Member ASHRAE This two-part series discusses solid-state lighting and its envisioned use and benefits in U.S. buildings. This article covers solid state lighting’s current and emerging applications. Inorganic LEDs: Weighing Costs and Advantages I n several specific lighting applications, light emitting diode (LED) products are at least as efficient as traditional technologies. Also, LEDs have a longer life span, require less maintenance, are vibration-resistant, contain no mercury, and do not emit infrared (IR) or ultraviolet (UV) light. Incandescent bulbs convert 8% of their power to visible light, while fluorescents convert 21% and LEDs convert 15% – 25%, with projections of 50% in the coming years.1 With their benefits over conventional lamp technologies, LEDs are being engineered to be superior solutions in several applications. Outdoor Lighting U.S. street and parking area lighting accounts for 178 TWh annually, roughly 23% of total lighting energy consumption.2 Its main purpose is to illuminate roadway, sidewalk, and parking lot surfaces, providing improved visibility and safety conditions for drivers, pedestrians, and occupants of adjacent buildings. Most of these outdoor lamps are metal halide (MH) or high-pressure sodium (HPS) sources. These relatively efficient technologies have a lifetime of about 25,000 hours and a reasonably low cost per kilolumen. However, they have a number of disadvantages, including a lengthy warmup time, preventing instant-on, as well as a significant restrike delay, which is 78 ASHRAE Journal required to allow the bulb to cool before it is relit. Also, the surface lighting is very uneven, providing intense lighting directly underneath, while relatively dim at greater angles from their nadir. This nonuniformity requires the human eye to drastically adjust between these relative intensities, causing reduced visibility. Finally, conventional street lamps may contain mercury and lead, potentially harmful metals. LEDs provide lumen levels equivalent to conventional outdoor lighting technologies, but can do so with greater efficacy.3 This is likely their most well-known and appreciated benefit, which can provide a reduction in energy consumption. Other ashrae.org benefits of LEDs also make them well suited for this application. LED luminaires used in outdoor lighting are able to immediately turn on and off, eliminating warm-up times and restrike delays. This enables energy-saving techniques such as motion sensing in parking lots that requires more frequent switching on and off of the source. Additionally, LEDs are dimmable, allowing a change in lighting intensity, and, therefore, power draw, based on motion information. When no motion is sensed in the vicinity, the light can be off or dim. These techniques can significantly reduce over-lighting empty, unoccupied spaces, and save energy. Due to the long running hours and high wattage of these lights, this can substantially reduce the payback period for properly installed systems. Outdoor LEDs also have longer lives, some more than 150,000 hours, when properly engineered for junction temperature and drive current limits. This results in a reduction in maintenance and replacement costs, which can surpass energy costs in MH or HPS installations. Outdoor LED luminaires have many individual point sources, allowing them to be arranged for more uniform surface lighting than MH or HPS systems can be, improving visual conditions and driver safety on roadways. In addition, LED sources in a luminaire can be arranged to prevent lighting unwanted areas. For instance, light trespass and spillage are seen as a concern in some metropolitan areas, with roadway and parking area lighting contributing. The inherent directionality of LEDs gives luminaire designers much better control of radiance angles and relative surface intensities. The U.S. Department of Energy (DOE) estimates that 45 TWh per year could be saved through the adoption of LED street and area lighting and another 13 TWh per year could be saved by applying LEDs to step, path, and porch lights. 4 This neglects further reductions that could be February 2010

ASHRAE Journal - February 2010

Table of Contents for the Digital Edition of ASHRAE Journal - February 2010