LED lighting is the newest lighting innovation, offering lights that last for many years, use as little as one-tenth the energy of normal light bulbs, and contain no environmentally damaging mercury. Because the technology is both new and different, many questions remain about how to best to use LEDs, what factors to consider when choosing an LED lamp, and what the fundamental product choices are.
Below are two illustrative LEDs. The one on the left is and example of a bulb design, an HP-Globe 15, a 15 watt LED that produces as much light as an 85 watt incandescent. The lamp on the right is and HP-10 Flood, which uses only 10 watts to put out as much light as a 50 watt incandescent lamp.
LED lighting refers to light-emitting diodes, a technology originally developed by a British researcher in 1907 (1). LEDs are semiconductors that emit light when a current is passed through them. The challenge over the years has been two-fold: first, the amount of light that LEDs emit has historically been very low, in fact, until recently, the light levels were too low for LEDs to be considered a replacement for standard lighting sources. Secondly, the color emitted by the LEDs in the visible spectrum has been limited to very specific colors, beginning with red in 1962 followed by yellow and blue. It has only been in recent years were a variety of colors have been developed, enabling the generation of useful white light, for example. These innovations in light levels and colors have enabled LEDs to be adopted for use as light sources for illumination in consumer applications.
Characteristics of LEDs
- Efficiency - LEDs are much more efficient than both compact fluorescent light bulbs and incandescent light bulbs. For example, in a typical high use are in your home, a standard 100 watt incandescent light bulb may cost $23.36 to operate for a year, while a comparable compact fluorescent light bulb at 23 watts would cost $5.37 to operate for a year, and a comparable LED at 13 watts would cost $3.04 to operate for a year, saving 87% of your electricity costs!
- Life - A standard incandescent bulb may operate for only 750 hours, while a compact fluorescent operates and 10,0000 hours, and a comparable LED operates for 50,000 hours. That basically means that when you buy an LED, you might have it with you for between twenty-five and fifty years. If you use your LED for four hours per day, every day all year, the bulb will last for at least thirty-four years! With such a long life, LEDs can be very useful in hard to reach locations where replacement is difficult or costly.
- Beam Angle - LED lights are directional lights, meaning that the light is directed in a certain direction. The most basic application for illuminating LEDs is as spot lights, given the directional or focused nature of the light output. Consequently, when purchasing LEDs, they may have fewer lumens than a normal lamp, but the same amount of light may be directed to the work surface. An LED light is usually multiple small LEDs that project a conical shaped light pattern. In order to have the same dispersion as an incandescent light bulb, a frosted dome is placed over the end of the LED lamp. This constrains the light output of the LED, but provides a more generally dispersed form of light. Beam angles can range from 20 degrees up to 180 degrees.
- Color - When selecting light bulbs of any type or design, it is important to be aware of your choices with respect to the color characteristics of the lamp. Light bulbs use a color scale called kelvin, named after Lord Kelvin of Great Britain who developed "an absolute thermometric scale" in 184 equivalent to the scale of degrees celsius, except with the zero point being absolute zero, where all thermal energy of matter drops to zero. This zero point is approximately equal to 460 degrees below zero on the Fahrenheit scale. For lighting, the color scale typically runs from 2,500 to 7,000, with color rendition improving from the lower numbers up to the higher numbers. Compact fluorescents, for example, range from 2,700 to 3,000 kelvin, corresponding to what is referred to as warm light. Lamps with temperature ranges up to 3,500 kelvin have greater white light and can be good for reading lights. As the color temperature goes up between 4,000 and 6,500, the light goes from white to blue. These higher temperature levels are sometimes referred to as "daylight" colors.
- Types - LED lights come in several basic types, including bulb lights, flood lights, light bars, and bi-pin bulbs. What is important to note is that LEDs do not come in dimmable versions, although there are integrated lamp configurations which successively switch off individual diodes. These types of lamps are used in flashlights and headlamps. The light bar or strip light types can be good for under cabinets in kitchens, and can also be integrated into light fixtures for task lights used on working surfaces such as desks. Generally LEDs are good for spot light applications, track lighting, and accent lighting.
- Cost - LEDs are generally expensive, but prices are coming down rapidly, and performance is improving rapidly. Equivalent replacements for 100 watt light bulbs, for example, can cost between $80 and $120. These prices are coming down rapidly as performance improves and manufacturing volumes increase. A key capability that has improved in recent years is light output. As the lumen levels of LEDs increase, the cost performance is improving.
- Emissions - The emissions of LEDs is extremely low compared with other light sources. In the examples alluded to earlier, the standard 100 watt incandescent bulb, operating for four hours per day, is responsible for close to 200 pounds of CO2 emitted per year. The corresponding 13 watt LED is responsible for 25 pounds of CO2 emitted per year, a remarkable 87% drop in CO2 emissions per year.
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