LED Lighting 101
A light emitting diode (or LED for short) is a small electronic device (a semiconductor diode to be exact) that emits light when electricity passes through it. The color of the LED depends on the materials used during production. For example, a red LED is made from the chemical elements of aluminum, gallium, and arsenic. Other than red, LEDs also come in green, blue, and amber.
Can I Get That LED In White Please
Nope. While there is no white LED, which is considered the "holy grail" of LED light research by the way, white light can be produced by two different methods. One way is to cover a blue LED with a yellow phosphorous coating. Another is to place, red, blue, and green LEDs in close proximity to each other. Through this innovative combination of various-colored LEDs, dramatic color-changing effects can be produced from a single fixture through dynamic activation of various sets of LEDs. Several manufacturers offer track, theatrical, underwater, outdoor, and other LED fixtures utilizing variable-intensity LEDs that can provide more than 16.7 million colors, including white light. These LED fixtures can be individually controlled via a PC, DMX controller, or a proprietary controller to generate effects including fixed color, color washing, cross fading, random color changing, strobing, and variable strobing. Cool technologies, huh?
11 Advantages of LEDs
- Very long rated lives
- Small in size
- No restrike time
- Generate a lot less heat than other light sources
- Slow failure rate
- Shock resistant
- Work well in low temperatures
- Their light can be easily focused
- Do not attract bugs (since LEDs do not produce ultraviolet light)
Oh yea, and since they do not contain any mercury, they are less toxic than many other light sources (e.g., fluorescent, metal halide, and high pressure sodium) and, therefore, LED fixtures are a safer light to dispose of.
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Color Rendering and Color Temperature
A light source's color rendering index (CRI) is the measure of its ability to render color accurately. There is a scale that ranges from 1 (low pressure sodium) to 100 (the sun). A CRI of 75 is considered to be good, 85 is very good, 95 is excellent, and 100 is perfect. Many warm white LEDs are available with a CRI of 80 or higher.
Color temperature is the measure of the color appearance of a light source which helps describe the apparent "warmth" (reddish) or "coolness" (bluish) of that light source. Generally, light sources below 3200K are considered "warm;" while those above 4000K are considered "cool" light sources. The color temperature of a light source has nothing to do with how hot the light source will get or how much heat is given off by the light source. The letter, K, stands for Kelvin, a type of temperature scale.
LED lighting fixture technology enables a wide range of available color temperatures for white LEDs (e.g., warm white, neutral white, cool white, daylight). Since the "warmer" color temperature white LEDs need more yellow phosphor coating than the "cooler" color temperature white LEDs, the warm white ones are always less bright than cool white assuming all other variable remain constant. You may see some variation and color inconsistency among white LEDs. Check the color temperature of the LED light fixture you want to try. The temperature has 4 digits, and the higher the number, the bluer the light will look. Incandescent light is normally around 2700K-3000K and this is what you should look for if you want to emulate the "warm" look of incandescent light.
Myth Buster: There is Heat!
Contrary to some popular opinion LEDs do generate some heat. This heat comes out of the rear of the LED fixture and not the front and it needs to be carefully taken away from the LEDs and dissipated by using a well-designed heat sink of some sort. The existence of heat sink "fins" does not ensure that the LED light fixture has a good heat management system. The "fins" may have been added simply for aesthetic reasons in order to make the LED light fixtures look contemporary or "cool-looking". Remember, it is imperative to have good heat management solutions to maximize the life of the LEDs in the LED lighting fixture. If not, the life of the LEDs will be dramatically reduced if this heat is not managed properly. Keep in mind that the actual beam of light produced by an LED light fixture does not contain any heat since white LEDs do not emit any infrared radiation.
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Light Fixture Design
As we have said, a single LED is very small and produces little light overall. However, this weakness in LED downlight fixtures is actually its strength with regards to light fixture design. LEDs can be combined into any shape to produce desired lumen packages as the design goals and economics permit. Amazingly, white LEDs also produce minimal ultraviolet (UV) light. Thus, when using white LED light fixtures, there will be minimal fading and deterioration of fabrics, documents, or artwork due to exposure to the white light from LEDs.
Finally, unlike other light bulbs that use fragile filaments (especially incandescent light bulbs) LEDs tolerate vibration exceptionally well because they do not use filaments. Vibration or shock easily breaks the fragile filament in an incandescent bulb and the glass tubing of a fluorescent lamp. LEDs, on the other hand, are completely solid-state technology and are virtually indestructible.
How Long is a Long Life?
Add long-lasting to the list of features found in LED light fixtures for homes. Conventional incandescent light bulbs last around 1,000 hours. Normal screw-in compact fluorescent lamps (CFLs) last around 8,000-10,000 hours. White LEDs for everyday use in a well-designed light fixture should last at least 25,000 hours if not more. This long life translates into substantially reduced maintenance costs, especially for hard-to-reach light fixtures (e.g., traffic lights). Moreover, unlike with comparable fluorescent light bulbs, the life span of LEDs is not affected by turning them on and off in rapid succession. One more thing, LEDs will not burn out like conventional light bulbs. Instead, over their lifetime they simply get progressively dimmer until they do not emit enough light to be useful.
However, do keep in mind that since the buildup of heat is so detrimental to the life of LEDs, it naturally follows that LED replacement light bulbs for existing lights would probably last longer in open fixtures. For example, simple track lights that allow the air to circulate freely around the light bulb than in enclosed ceiling lights.
Just like a fluorescent light bulb cannot function without a ballast, which provides a starting voltage and limits electrical current to the lamp, LED light fixtures also require a similar electronic power source, called a driver. The driver converts line power to the appropriate voltage and current, and may also include dimming and/or color correction controls.
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More Fun Facts
We have mentioned that LEDs do not radiate high levels of UV rays. While it is common knowledge that heat can speed up food's spoilage rate, it is lesser known that high UV levels can actually decrease the nutrient levels in food. Thus, using LEDs to light the produce in a super market may not only be energy efficient, it may also help the produce to maintain higher nutrient levels. Yum!
LEDs make for better vehicle headlights. It is a safety advantage to drivers for purely physiological reasons. The higher color temperature of LED headlights compared to halogen and xenon improves driver vision in low-light conditions (twilight and darkness). Also, our peripheral vision is improved with the use of LED headlights. The high blue share of LEDs leads to higher sensitivity to potentially hazardous objects appearing in the lateral field of vision.
Finally, since there is no ultraviolet light white LEDs do not attract bugs. So, if all else fails, LEDs have this going for them.