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LED Frequently Asked Questions
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Q. What is an LED?
A. LED is the common abbreviation for a light-emitting diode. Each individual
LED consists of a semiconductor diode that emits light when a voltage is applied to it.
The electronics industry has used LED technology for several decades as indicator lights
for various electronic devices. In more recent years, LED technology has progressed to
the point where it is viable for general lighting applications.
Q. What color of light can LED emit?
A. Most LEDs are monochromatic. Light color is associated with the light
wavelength. LEDs made with different semiconductor materials emit lights in different
wavelengths. LED light wavelengths range from 400 nanometers (blue) to 800 nanometers
(red). The colors of popularly available LEDs in the market are red, orange, amber,
yellow, green, blue and white.
Q. Can LEDs be used to replace conventional incandescent and florescent light bulbs?
A. Yes and no. LEDs have increasingly been used in many different applications
to replace old incandescent light bulbs. Examples include LED indicator lights for all
kinds of electronic devices such as cell phone, calculators, automotive dash panel,
LCD back-lighting, etc., LED seasonal decoration lights for Christmas and holidays,
LED traffic signs and other LED direction signs, LED flashing lights, and so on. As
currently available LEDs have limited brightness, in most cases, they can not be used
to replace incandescent or florescent light bulbs for general lighting purposes.
Q. What are the advantages of LEDs compared with conventional incandescent lights?
A. There are several obvious advantages LEDs have over traditional incandescent
light bulbs, they are as follows:
Low power consumption - energy saving
Long lasting
Cold lighting
Ruggedness
Small size and weight
Fast switch times
Simple to use
Q. Could you give more detailed explanations about these LED advantages?
A. People can save money & energy by using LEDs instead of equivalent incandescent decorative bulbs.
The rated average working life of LED is 100,000 hours compared with 1,000 hours of incandescent bulbs.
LEDs emit cold lights as working LEDs generate very small amount of heat, so LEDs are much
safer than equivalent incandescent light bulbs in terms of danger of fire. LEDs don’t have
filaments to heat up in order to emit lights just like the case of incandescent bulbs. Lights
are emitted from LEDs as a result of energy exchange occurring in the different semiconductor
materials an LED is made of.
LEDs are usually shielded with solid transparent plastic materials so they are more rugged
than incandescent and florescent bulbs that are usually sealed with glass.
LEDs can be powered by either AC voltage or DC voltage. The circuit that is required to
appropriately drive LEDs is much simpler than that for florescent bulbs.
Q. How long is 50,000 hours?
A. Based on how long a fixture is illuminated per day, here's what 50,000 works out to:
24 hours a day = 5.7 years
18 hours per day = 7.4 years
12 hours per day = 11.4 years
8 hours per day = 17.1 years
Q. How do you evaluate LED products?
A. Lumen output is only part of the story and can be misleading. To fully evaluate
an LED product one needs to review the overall system efficiency, optical control, thermal
management of the LEDs, and know at what point in time the fixture will reach 30 percent
lumen depreciation. Products with good optical efficiency and thermal management will be able
to deliver more lumens, on average, than traditional HID products.
As the Department of Energy concluded in its Solid-State Lighting Commercial Product
Testing Program: "Until the field of SSL technologies and supporting knowledge matures,
any claims regarding performance of SSL luminaires should be based on overall luminaire
efficacy (i.e., from testing of the entire luminaire, including LEDs, drivers, heat sinks,
optical lenses and housing), to avoid misleading buyers and causing long-term damage to the SSL market."
Q. Where have LEDs been used in the lighting industry?
A. LEDs are commonly used in aesthetic, effect, or specialty lighting applications,
including architectural highlighting. Most traffic lights and exit signs, for example,
now use red, green or blue LEDs.
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