Light-emitting diodes (LEDs) are often touted for their energy efficiency and long life. Although these are important considerations, selecting a light source should involve many other factors. Let’s explores some of the unique attributes of LEDs, which may make them the best choice for a many applications.
Financial considerations—namely, purchase price and operating costs—always figure in the selection of lighting products, but many other aspects also come into play, varying in importance depending on the application. LEDs have several unique attributes, and it is critical to understand how they can be used advantageously. Some considerations are dependent on product design, but others amount to using LEDs in appropriate situations. Some of the potentially favorable characteristics of LED sources com pared to traditional lamps include:
LEDs are semiconductor devices that emit light through electro-luminescence. LEDs rely on injection luminescence, a specific type of electroluminescence. In this case, light is generated directly when electrons recombine with holes, in the process emitting photons. For more on the physics of LED light generation, see the IES Lighting Handbook or other reference sources. This basic fact is the foundation for many of the advantages of LEDs, since it is different from traditional light sources. For example, incandescent lamps rely on a heated filament to emit light, fluorescent lamps create light using a gas dis charge to excite phosphors, and high-intensity discharge (HID) lamps utilize an electric arc discharge. All of these traditional technologies require a glass bulb to contain essential gases and/or coatings.
In contrast to the large form factors of traditional lamps, LED lighting starts with a tiny chip (also called a die; most commonly about 1 mm) comprised of layers of semiconducting material— the exact material determines the wavelength (color) of radiation that is emitted. At the next level are LED packages, which may contain one or more chips mounted on heat-conducting material and usually enclosed in a lens or encapsulant. The resulting device, typically less than 1 cm, can then be used individually or in an array. Finally, LEDs are mounted on a circuit board and incorporated into a lighting fixture, attached to an architectural structure, or made to ﬁt the form factor of a traditional lamp (or as it is commonly known, a light bulb).
The LED product market continues to grow rapidly. In many applications, today’s high-quality LEDs can outperform traditional technologies when evaluated with conventional metrics including efficacy, color quality, and operating cost. However, LED products have significant variation in performance from one product to the next. Thus, generalized comparisons are often misrepresentative. When purchasing or specifying LED products, it is essential to evaluate appropriate data