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October 21st, 2008 admin Leave a comment Go to comments

Led Flickering

LED Lighting: Basic Facts for First-Time Buyers

Because of their many advantages over traditional incandescent and fluorescent light bulbs, LED lights are poised to transform all forms of lighting. Selecting and purchasing LED lights requires buyers to learn new terminology and take into consideration factors that they don't have to think about when buying traditional types of lighting. This brief article provides some basic background and purchasing considerations for first-time buyers of LED replacement lights.

As most people probably know by now, LED stands for light-emitting diode. LEDs are actually semiconductors (just like computer chips) that produce light more efficiently than traditional light sources. When electricity is passed through them, they emit energy in the form of light. These semiconductors are doped or injected with chemicals that determine their light color. LEDs convert the majority of energy passed through them to light, as opposed to incandescent bulbs that produce light as a by-product of being heated. For this reason, LEDs can be up to 90% more efficient than traditional household filament light bulbs.

LEDs have been widely used in as displays and indicator lights for nearly 40 years. Only recently, though, have engineers figured out how to make and mass-produce bright, white LEDs that can be used for general-purpose lighting. The high brightness and point-source characteristics of LEDs have made them the first choice for traffic lights and car tail lights, where visibility and dependability are essential.

So, what should you know when purchasing LED lights bulbs? The following list provides some basic guidelines:

1. While the initial cost per bulb is still high, the total lifetime cost of an LED light bulb is actually lower than that of equivalent incandescent and CFL bulbs. Taking into consideration energy costs as well as time and resources required to replace incandescent and CFL bulbs, an LED bulb that lasts 80,000 hours has a much lower lifetime cost.

2. LEDs are diverse, and - as unlucky purchasers are all too likely to find out the hard way - many types are useless for general lighting applications. The finest LED chips emit light with a Color Rendering Index (CRI) of 85%. The CRI, by the way, is a quantitative measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source. LED light bulbs that use top-quality LEDs will last much longer than the novelty bulbs that many are selling and 60% longer than many competing bulbs that use inferior LEDs.

3. Contrary to what you may read some places, LEDs do generate heat, and this heat is actually the biggest problem that manufacturers face developing LED lighting applications. Manufacturers can now produce individual LED chips that are as bright as a 100-watt incandescent bulb, but these LEDs are practically useless for general lighting because installing them in a fixture creates ventilation problems that have not yet been solved. LEDs installed in fixtures and bulbs must be ventilated properly, and the better the chip, the more difficult it is to properly cool. There are many LED light bulbs on the market that do not take this into consideration and either use cheap chips so they don't have to ventilate them, or do not ventilate their chips properly, significantly reducing its lifespan. While the typical LED light bulb is barely warm to the touch, if the chip is not properly ventilated, it can fail prematurely.

4. While LED light bulbs do last much longer than conventional bulbs, look closely at manufacturer claims for bulb life. The life-span of an LED light bulb should be its "half-life." LED light bulbs do not burn out; rather, they gradually fade out. When a vendor says an LED bulb will last 80,000 hours, they mean that at that point, the chips will have reached 50% efficiency, and the bulb ought to be replaced. So, the bulb might last 100,000 hours or more, but its efficiency will have degraded greatly by that point. Using this 100,000-hour life as a selling point is therefore misleading. While LEDs don't last forever, they will last 50-75 times longer than a comparable incandescent and 6-8 times longer than a CFL.

5. Searching the web, you will quickly find that the LED light bulb market is inundated with product. Many of these bulbs are relatively inexpensive (less than $20); however, you may find that many of these LED bulbs consist of questionable materials and dubious craftsmanship. Good LED light bulbs cost more than these cheap ones because they use high-quality chips with prices firmly set by reputable manufacturers like Cree. This means that though these LED light bulbs are more expensive, they are far superior.

6. LED light bulbs can't be dimmed with traditional dimmers. LEDs require constant current to operate. Because of this, if a standard dimming method is applied, it will flicker at regular intervals, or worse, simply not work. In order to dim an LED light, a 0-10V dimming module is required in order to "trick" the LED into emitting less light. In theory, all LED lights are dimmable with this module.

7. When comparing LED light bulbs, you need to understand lumens. The lumen is a standard unit you can use to compare LED light bulbs to standard bulbs, such as incandescents and halogens. Roughly, a lumen is a measure of brightness. Lumen quantity is important, but maybe more important is lumen quality, i.e., luminous efficacy (lumen/Watt). Today's quality LEDs have a luminous efficacy between 60-70 lumens/watt.

8. Color temperature and beam spread are the other key tools for comparing LED lights. Both color temperature and beam spread are measured in degrees. Color temperature refers to the color of the light emitted. In general, 3000 Kelvin is warm white (closer to infrared light) and 5000 Kelvin is cool white (closer to ultraviolet light). Cool white is brighter because it is the natural color of LED light, whereas chips that emit a warm white light require a phosphorous "filter" to "warm" the color temperature, thus reducing the chip's brightness. Beam spread is the angle of the light that is being emitted. The lower the number, the more like a "spot" the light is.

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