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| Fig. 1: A schematic of the interworking of LED light source. (Source: Wikimedia Commons) |
As we light up our spaces, the power to do so is often overlooked. On the surface a 60W incandescent light bulb wouldn't seem like it would be using as much energy as other household items such as a 1000W air conditioning system. Due to the amount of bulbs used to light up a space and the length of time that lights are commonly on for, lighting is the second largest amount of energy usage in buildings. [1] Therefore, it is important to adopt more efficient technologies that can yield substantial energy savings. When looking at the common light bulb options, the three most common are Incandescent bulbs, Compact Fluorescent Lamps (CFLs), and Light Emitting Diodes (LEDs). The drawback to Incandescent bulbs is that only about 5% of the input electrical energy is converted to visible light, and the rest is emitted as heat, so the incandescent light bulb is 95% inefficient at producing light. [2] Even energy-saving compact fluorescent lamps (a phosphor-coated gas discharge tube) are only about 20% efficient. [2] The drawbacks to CFLs are the time it takes for the electricity to start flowing and become fully lit, as well as the dangers posed with the mercury inside the bulbs if one were to break. LEDs on the other hand, use light emitting diodes to produce light very efficiently. LED lighting, when compared to both Incandescent and CFL bulbs, is seen as more efficient, durable, versatile, and longer lasting.
As seen in Fig. 1, LEDs are semiconductor diodes, which are electronic devices that permit current to flow in only one direction. The diode is formed by bringing two slightly different materials together to form a PN junction. A PN junction is used to inject carriers (holes and electrons) into the active layers from p-type layer and n-type layer. [3] As this occurs, energy is released in the form of light that is emitted by the LED. Since LED lighting systems don't radiate heat the way an incandescent or CFL light bulb does, the heat produced from the power going into the product must be drawn away from the LEDs. This is usually done with a heat sink, which is a passive device that absorbs the heat produced and dissipates it into the surrounding environment. [4] As a result, this allows the LEDs to keep from overheating and burning out.
When looking at the long life spans and energy first choice when purchasing new bulbs for an area. As research continues, LEDs continue to improve and be used in new applications. With this new use for applications, there has been a major shift towards LEDs as a way to light everything from holiday lights to traffic signals. Due to the construction of LEDs, their ability to be efficient, durable, versatile, and longer lasting gives these bulbs a competitive edge when compared to the competition.
© Bret Bonanni. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] "Lighting Efficiency," Pew Center on Global Climate Change, April 2011.
[2] C. J. Humphreys, "Solid-State Lighting," MRS Bull. 33, 459 (2008).
[3] S. Nakamura, "The Roles of Structural Imperfections in InGaN-Based Blue Light-Emitting Diodes and Laser Diodes," Science 281, 956 (1998).
[4] N. Narendran and Y. Gu, "Life of LED-Based White Light Sources," J. Disp. Technol. 1, 167 (2005).
