Making sense of LED technology
February 6, 2008
Lighting technology has be stagnant for over 100 years. Compact fluorescent lamps are now common place in most stores but a few years ago you couldn't buy anything but an incandescent light bulb. After just being introduced to the CFL after 100 years of the same technology consumers are now being introduced to a LED lighting technology. This Christmas news about LED lights was published in most all major media markets and most big box retail stores stocked some LED Christmas tree lights. Christmas was just the beginning of a huge push by manufacturers and lighting technology companies to introduce consumers to a new and unfamiliar technology. Like many new technologies, LEDs are being improved all the time and the technology is moving forward very quickly. As a result, there is a lot of information out there that is somewhat contradictory, confusing, or difficult to understand. The two most commonly misunderstood aspects of LED lights used for holiday decorating are: 1) LED lamp life; and 2) "Full Wave" rectification.
LED Lamp Life
One of the principle benefits of LED lighting is that they will last substantially longer than all other types of lighting technology available today. However, there is a wide range of opinion, claims, and statements about the life of LED lamps. This issue is exacerbated by the fact that even LED lighting experts do not agree about when the useful life of an LED has ended. This is because LEDs do not simply burn out like standard incandescent lamps; rather, LEDs begin to loose their brilliance and their lumen output decreases over time. The claims about LED life range from as little as about 20,000 hours to as many as 200,000. That being said, all LEDs are not create equal but in general there are several factors that effect the useful life of an LED, incluing:
- LED chip quality
- Color of LED
- Amount of power sent to LED
- Environment and temperature
For example, LEDs are extremely sensitive to heat so a LED housed in a fixture that dissipates heat well will last longer. Using another example, some LEDs are powered at levels approaching 95% or more of the chips capacity. A LED chip that is powered at a lower level--say 80% of its capacity--will last longer. All these factors affect the life of an LED. In the Christmas and holiday lighting industry, claims of LED lamp life of more than 100,000 hours are common. Most holiday and decorative LED products currently on the market will begin to experience substantial lumen reduction after 50,000 hours. But even 20,000 hours is a very long time and can add up to substantial savings and huge environmental benefits in the long term. This past December Alexander Karsner, Assistant Secretary of Energy, appeared on NBC to discuss the the benefits of LED holiday lighting.
"Full Wave" LED Christmas Lights
"Full Wave" is a term that is now being used to describe and market a certain type of LED holiday lighting. A complete explanation of the technology that is described as "full wave" requires a discussion about the LED technology that is beyond the scope of this article. (Howstuffworks.com has a decent article about the physics behind LED lighting for those who are interested.) Simply put, all LEDs flicker. That is, they turn on and off at a very high rate of speed. A standard LED that is not rectified flickers 60 times per second. This is so fast that the average human eye cannot detect the flicker under normal conditions. However, if the LED product is moving the flicker may become more visible. A "full wave" LED uses a device called a rectifier to increase the rate at which the LED flickers to 120 times per second. An a LED that flickers at 120 times per second is undetectable by the human eye. A fully rectified LED light has a few advantages:
- It produces between 30-40% more light output
- Has no visible flicker in windy conditions which are common in outdoor Christmas lighting environments
The downside of full wave LED lights is that it reduces the lamp life because the LEDs are driven twice as hard. A standard 1/2 wave LED is essentially off half the time because of the flicker rate. A fully rectified LED is on twice as long and therefore will not last as long.
Whether or not you should choose a fully rectified LED holiday light or a standard 1/2 wave light for your Christmas or holiday decoration depends on the application, sensitivity to flicker, and price. (Fully rectified LEDs are usually a bit more expensive.)