A light-emitting diode (LED) is a solid-state device that emits monochromatic or single-color light when a prescribed voltage is applied to its terminals, and its technology has been around for decades. For many years, LEDs were used as indicator lights and digital displays on equipment and appliances. In the 1990s, the discovery of the blue LED led to the development of a white LED. The ability of an LED to produce a white light coupled by increasing light output and decreasing costs opened the way for LED technology to evolve into a mainstream light source. Steady advances over the past 50 years have set the stage for a revolution in the lighting industry that has already begun and is picking up speed.
The pros and cons of LEDs
LEDs have a number of advantages over traditional light sources. First, LEDs are much more efficient on a lumens-per-watt basis. LED light sources have life expectancies expressed in decades rather than hours or years. Since LEDs are solid-state devices, they are much more rugged and resistant to damage. Finally, LED light sources give off much less heat during operation, allowing installation in locations and around materials that would not be possible for traditional light sources.
Despite their advantages and increasing popularity, LEDs still have a number of drawbacks that must be overcome before they will replace traditional light sources in most residential and commercial applications. Even though LED light sources are significantly more efficient on a lumens-per-watt basis, they are currently unable to deliver the same light intensity as traditional light sources. This limits the use of LED light sources when intense or high-ambient lighting is required. Furthermore, white LEDs produce a “cool” light, making them undesirable where high color rendition is needed. Finally, LED light sources are considerably more expensive.
The drawbacks are currently the focus of a great deal of research and development because LEDs show such promise as the artificial light source of the future. Today, higher output LEDs are commercially available, and research and development continues to make advances in this area. Similarly, LED light source color is improving and manufacturers are beginning to offer warm white LEDs. In the future, there will probably be a wide variety of LED light source spectrums to choose from just as there is for fluorescent and metal halide lamps today. Finally, as manufacturing processes improve and demand increases, the unit cost of producing LEDs will continue to decrease.
LED light sources today
The LED light sources are first being used in applications where their advantages overcome their disadvantages. Their long life and resistance to mechanical damage makes them ideal for building outline and decorative lighting where access is difficult and maintenance is expensive. Similarly, emergency and safety lighting—where reliability is important and low-light levels are acceptable—makes LED lighting a good fit for exit signage, egress lighting, outdoor walkway and step lighting.
For outdoor lighting, LED light sources are being paired with photovoltaics, eliminating the need for branch-circuit wiring and taking advantage of the LED light source low-power requirements and direct use of the DC power supplied by the PV/battery system. Manufacturers are now producing standards with LED light sources for walkway, roadway and parking lot lighting. LEDs are finding applications wherever color rendition is not important, ruggedness and the cost of maintenance are issues, and a lower intensity light source is acceptable.
In addition, LED lighting is rapidly becoming the light source of choice for both indoor and outdoor architectural lighting as more building and landscape architects, lighting designers and interior designers learn about and gain experience with it. One drawback, such as LED lighting’s monochromatic nature, which makes it ill fitting for general, task and accent lighting consequently makes it ideal for architectural lighting where LED light sources, coupled with controllers, can create a spectrum of colors for washing walls or creating a dynamic visual environment. With LED light sources and today’s controllers, any color can be achieved without colored lamps or filters that take up space, are limited in their spectrum, are inefficient and are difficult to hide from view.
Today, a number of manufacturers are producing LED lamps for general and task lighting. LED lamps come in all standard sizes and shapes and are designed for use in standard luminaires such as downlights and track lighting in lieu of incandescent, halogen and compact fluorescent lamps. Most of these LED lamps and luminaries are designed to operate at a standard 120 volts, but there are some available that will operate at standard low voltage, 277 volts, or even a range of voltages. EC
This article is the result of a research project investigating future markets for the electrical contractor that is being sponsored by ELECTRI International Inc. The author would like to thank the foundation for its support
GLAVINICH is an associate professor in the Department of Civil, Environmental and Architectural Engineering at The University of Kansas. He can be reached at 785.864.3435 email@example.com.