UL article on LED

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Asia On The Mark Issue 26 (Summer 2008)
Safety Standard Requirements for LED Lighting Products
Having the advantages of energy saving and being environmentally friendly, LED lighting products have become mainstream devices in the lighting industry. The attributes and technology to which LED lighting products are based upon are different from those of conventional lighting products, as a result existing safety standards for general lighting products are not applicable. This article discusses the LED technology and potential lighting applications of LEDs and current safety assessments for LED lighting products by UL.
LED lighting technology and properties
As named, LED lighting products use LEDs (Light-emitting Diodes) as the main lighting source. An LED is a semiconductor diode. When a current flows in the forward direction across the p-n junction, the negative charge (“electrons”) and the positive charge (“holes”, indicating the absence of electrons) will meet and release photons and thus emit light. The material used in the semiconducting element of a LED determines its color. Colors of the LEDs range from infrared to blue and from violet to ultraviolet, depending on the wavelength of the light emitted. A recent development is phosphor coating on LEDs illuminating blue light to produce white light. To achieve this, an LED driver or power supply will be required to convert alternating current to direct current and at the same time provide the LED device with the appropriate voltage and current to drive the relevant parts.
LED light bulbs are small in size, light in weight and sealed in epoxy, which can withstand strong mechanical impact and vibration and thus are not easily breakable. LED light bulbs also have a long beam lifetime between 50,000 and 100,000 hours, far surpassing incandescent light bulbs at 1,000 hours and fluorescent tubes at 10,000 hours. An LED lighting product lasts from 5 to 10 years and can significantly reduce replacement costs.
In addition, LED lighting products consume much less energy for the same lighting effect; energy consumption of an LED light bulb is half of that of a fluorescent tube. Hence, LED lighting products have the advantage of energy and resource saving.
In the early days of development, LED applications in lighting products had their technological shortcomings, such as poor light quality (color rendering, consistency and color temperature), poor heat dissipation and high price. Improper heat dissipation can lead to accelerated decrease in brightness and life of components on the circuit.
Production technology of LEDs leapfrogged in the last decade. Disadvantages mentioned above have been overcome with lower heat resistant and better light quality. In 2008, luminous efficiency of cool white LED light bulbs reached 100 Lm/W. It is estimated that by 2010 luminous efficiency of warm white LED light bulbs will be improved from the existing 70 Lm/W to 100 Lm/W. Incandescent light bulbs have a luminous efficiency of about 15 Lm/W, fluorescent tubes 45-60 Lm/W and HID bulbs 120-150 Lm/W. In comparison with these general lighting products, luminous efficiency of LED light bulbs is obviously very competitive. See below table how LED bulbs compare with other general lighting products:
Lighting Product Characteristics
White LED light bulb Generate less heat, versatile in use, compact in size, shock resistant, focussed light beam
Daylight fluorescent tube Save energy. However, they are fragile and when disposed of, mercury pollution is an issue
Incandescent light bulb Low efficiency, high energy consumption, short life, fragile
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