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Although the birth of the lighting industry happened in the late 19th Century when Thomas Edison invented the incandescent light bulb, the rebirth of the industry is starting to take place right now as light-emitting diodes (LED)-based lighting fixtures continue making their way into the market. Those little LEDs that we became familiarized with in flashlights, indicator lights and electronic products are so bright that they are starting to be used to replace traditional light bulbs in lighting fixtures. In fact, the sources are so bright that they can be used in outdoor lighting fixtures to provide general nighttime illumination.
New solid-state lighting (SSL) technology has the potential to significantly revolutionize how the lighting industry manufactures—and customers use—lighting fixtures. SSL fixtures have a number of benefits that make them uniquely suited for outdoor applications. Reduced maintenance, directional output, energy saving and application benefits are all significant characteristics that make SSL fixtures attractive for outdoor use.
Maintenance benefits
One of the most prominent benefits of LED lighting sources is the long life of the technology. Understanding what lifetime means with SSL products is of paramount significance to fully comprehending the data that is presented by fixture manufacturers. An LED does not suddenly burn out like traditional lighting sources (incandescent, CFL, HID). Rather, the devices will gradually become dimmer over time and eventually reach a point where the light is no longer useful.
LED lifespan standards have not existed up until now. There have been many early numbers published by LED manufacturers and fixture manufacturers in recent years that do not necessarily present useful data with regard to LED life. It is now generally understood that due to some of the temperature constraints of the technology, the life of LEDs will never reach numbers like 100,000 hours in terms of useful light output.
Standards on reporting life data, which are due out in mid-2007, will require reporting the life at which the LED sources will maintain at least 70 percent of their initial lumen value. This gives designers and specifiers useful numbers to assist in any photometric calculations to ensure they will always have adequate light output. Proper thermally-managed LEDs should provide approximately 40,000 hours to 50,000 hours of illumination (at L70, maintenance of 70 percent of the initial lumens) when incorporated into an SSL fixture.
For a lighting fixture that is used in outdoor applications where the fixtures are typically left on for long amounts of time or in hard-to-reach areas, the benefit of having a source that lasts 40,000 hours is great. The majority of commercial outdoor applications have utilized HID sources such as metal halide and high-pressure sodium largely because they are high-illuminance sources that last approximately 10,000 hours.
SSL products surpass HID lifetime by at least four times and uses less energy. Moreover, it is estimated that by 2010, LEDs will surpass the efficacy LPW (lumens per Watt) levels of the HID sources as well, thereby creating an even greater efficiency story.
A typical outdoor fixture used in a commercial application is on from dusk until dawn. Therefore, the fixture will be operating approximately 12 hours per day. In an SSL fixture using an LED source that lasts 50,000 hours, this increases the operating time of the lamp source to 11 years, whereas the typical incumbent technologies of HID and CFL would be approximately two years.
One such application, which was one of the first to take advantage of SSL technology in a landscape fixture, is the Greenville-Spartanburg International Airport in Greenville, S.C. It features Kim Lighting's Scarab LED landscape accent fixture to provide years of efficient illumination in the main airport entryway.
The fixture, which is constructed from specification-grade die-cast aluminum, uses a cluster of six LED sources to illuminate the landscaping features. The durability of the lighting fixture coupled with the long-life LED technology create a fixture application that will require very little maintenance and no lamp replacements for 11 years. Such maintenance benefits are very attractive to building owners.
Directional benefits
One of the many issues that have surfaced in recent years is the proliferation of light pollution from the various artificial lighting sources. In most major cities, the nighttime skies are so polluted from man-made lighting that the stars are not viewable. Moreover, the phenomenon of light trespass (light shining into areas where it was not intended, such as a baseball field lights shining into a residential backyard) and glare (blinding bright light from fixtures that are not properly shielded) are becoming growing lighting concerns around the world.
Combating light pollution has become a primary mission for groups such as the International Dark Sky Association (IDA) which helps to educate and alleviate these poor lighting applications. Many municipalities have enacted ordinances that only allow lighting fixtures that are fully-shielded or have a full cutoff. Such fixtures will shine light only onto the areas that the fixture is intended to illuminate which is normally directly downwards.
Unlike traditional lamp sources that emit light in all directions, LED sources emit light only in one direction. Such directionality of the LED is an advantage in outdoor lighting fixtures that intend to be dark-sky friendly as they emit light patterns directly towards the desired illumination target and not into the sky.
Furthermore, directionality aids in energy savings because energy isn't being used to emit light beams that are trapped inside the fixture, thereby wasting lumens that are produced. By pushing all of the light directly outwards, an SSL fixture produces many more usable lumens and takes greater advantage of a fixture's energy consumption used to create visible light.
Energy-savings and environmental benefits
SSL fixtures use only a fraction of the energy used in traditional lamp technologies to create light. For every 1 watt of power used to create light in a traditional source such as metal halide, the lamp produces approximately 80 lumens of light.* With compact fluorescent, every 1 watt of power produces about 66 lumens of light.** Current technologies allow up to approximately 70 lumens of light per 1 watt*** from the latest cool white LED sources incorporated in SSL fixtures.
As mentioned earlier, less lumens are required to create adequate light levels in SSL fixtures due to the directionality. Therefore SSL outdoor fixtures using only 5W to 20W of power consumption can now recreate the light levels created by the same fixtures that were using incandescent and compact fluorescent sources. Technology advancements in LEDs are allowing the brightness levels to increase very rapidly. Soon the technological advances will allow HID fixtures to be replaced by lower-wattage SSL products of equivalent brightness.
The efficiency of the lumen values for the sources is expected to meet the HID lumen levels by approximately 2010. At this point, there will be a significant advantage to replacing many fixtures using HID sources such as street lights and wall packs due to the advantages of SSL technology.
Environmental concerns also will play a major role in the adoption of SSL products. Mercury, a substance that is present in most fluorescent and HID lamps, is considered a health concern and hazardous waste by some states. Fixtures and lamps that contain mercury require special labeling and disposal in many parts of the country.
LED sources generally contain no mercury or additional substances that would be considered harmful to the environment. Therefore, SSL fixtures are green-friendly, and contribute to a healthier environment both by consuming lower energy and containing no mercury.
Application benefits
LEDs have a number of unique characteristics that allow better performance in some outdoor applications than traditional technologies. The durability of the LED device and the operating temperature characteristics are great benefits in outdoor applications.
As LEDs contain no filaments or significant glass bulbs, there is little chance of breakage like you would have in a traditional light lamp. The tiny LED devices are very rugged, and can be literally dropped, tossed or shaken without sustaining any damage. This is very different than the fragile nature of traditional sources which can be easily broken or damaged in shipment or operation. Furthermore, the rugged LED characteristics mean that there is a far less chance that any vibrations present at the application area (such as a parking garage) could damage the LED sources.
Extreme cold environments can sometimes create significant problems for outdoor fixtures. Particularly regarding outdoor fixtures that utilize fluorescent lamps, the starting temperature requirements of standard fluorescent ballasts may prohibit such fixtures from being used in extreme cold temperature environments.
LEDs actually perform better and more efficiently in cold conditions. LEDs are essentially electronic chips and much like computers and similar products, they like the cold and need to be kept cool to operate properly. Conversely, it should be noted that sustained extreme hot environments such as the middle of summer in Arizona, may present some particular design challenges for SSL fixtures as maintaining certain internal temperatures of the LED device is extremely important in maintaining light levels and lifetime.
As manufacturers, specifiers and installers become more familiarized with the many benefits LED sources and SSL fixtures offer, these outdoor lighting products will increasingly become a part of the industry's landscape. As with any similar new technology in its inception, the pricing will be an initial hurdle but the long-term benefits far outweigh most initial pricing concerns.
The technology and the products are certainly now available and will become increasingly implemented in outdoor lighting applications in the coming years. Those little LED sources are not only for flashlights anymore. LED lighting fixtures are here and ready to illuminate the great outdoors.
Chris Primous is product manager at Hubbell Lighting Inc. for the Progress Lighting brand's LED, Commercial and Energy Star products.
author: By Chris Primous