Advantages and Weaknesses of LED Application

ivan — Thu, 20 Dec 2007 09:51:02 +0000

Unlike conventional incandescent lamps which need to convert the electricity into thermal energy first and then to light, LED illumination is achieved when a semiconductor crystal is activated so that it directly produces visible light in a desired wavelength range. With the continuous development of lighting technologies, more possible future applications of LEDs will be seen. Advantages and disadvantages of using LEDs are to be discussed as follows.

Advantages of LEDs

1. Long Life Span
The lifetime of conventional incandescent lamps is usually 3,000~4,000 hours. The ETTF (Estimated Time To Failure) of a LED is as long as 100,000 hours, which is much longer than that of incandescent lamps. Suppose we let a LED work four hours a day, we may have it work for us for more than 60 years.

2. Energy Saving and Low Cost
Generally speaking, LEDs are designed to operate only with 12~24V, and LEDs produce more light per watt than incandescent bulbs. High efficacy with low voltage makes LEDs easily overtake that of conventional incandescent lamps, consuming 80% less electrical power. Although High-Brightness single-color LEDs are more expensive than conventional incandescent lamps at present, they save much more electrical power, which can offset the price gap. Suppose a LED requires 15W to reach a certain luminance; for a conventional incandescent lamp, to reach the same level of luminance, it may require up to 150W.

3. Far More Environmentally Friendly
Unlike incandescent bulbs and fluorescent lamps, LEDs emit light in a different way. LEDs needn’t a filament that will burn out, and they don’t get especially hot, and no venomous gas will be yielded. Being solid state components, LEDs are difficult to damage with eternal shock. They are illuminated solely by the movement of electrons in a semiconductor material, and they last just as long as a standard transistor.

4. Good Environmental Adaptability
LEDs operate well in a large range of temperatures, -40℃~+85℃, with the humidity below 65%. So LEDs can be used in relatively harsh environment.

5. A Variety of Applications
LEDs have advanced from use in numeric displays and indicator lights to a range of new and potential new applications, including architectural lights, exit signs, accent lights, task lights, traffic lights, signage, cove lighting, wall sconces, outdoor lighting and down lighting, etc.

Weaknesses of LEDs

1. Bad Color Revivification
The general color rendering index of LEDs was relatively low in the past, and the color revert of LEDs is worse than incandescent bulbs.
We all know that the light quality of incandescent lamps is excellent (CRI 100%) while white LEDs provide color rendering indices between 70% and 85%, better for daylight (6,000 K) than for warm white (2,900 K) LEDs. However, with the improvement of phosphors and LED materials technology upgrade, some LEDs’ CRI has been enhanced to 90%.

2. Single LED’s Power is still Low
Due to the low power of single LED, the luminance of single LED is not high. Thus, more LEDs are required to be connected in parallel, such as automobile back lights. More LEDs lead to more cost although one single LED is not so expensive. At present, a single High Power LED is quite expensive yet its luminous intensity is just around 5,000 mcd.

3. Short Illumination Distance
Although many of the LED light source method can improve brightness, we find it difficult to extend their illumination distance. Because what LEDs emit is scattering light, the illumination distance is only tens of meters. Thus, LEDs are quite suitable for short distance lighting application. Nevertheless, with the development of technology, LEDs’ illumination distance will be extended step by step.

4. “Yellow Ring” Phenomenon
Due to the immature process of white light LEDs and the error when configure the reflective cup and lens, “Yellow Ring” phenomenon frequently appears when white light LEDs work, which is hard to eliminate. In recent years, blended phosphor has been adopted to generate ideal white light with high CRI.

Take blue light LED for example. It activates the mixture of YAG phosphor and green or red phosphor to generate white light. If the blue light LED, after activating YAG phosphor, emits white light with “Yellow Ring”, producers may add green light (wavelength 500nm～530nm) phosphor to counteract the unwanted yellow light. If the blue light LED, after activating YAG phosphor, emits white light with “Blue Ring”, red light phosphor without sulfide may be added to counteract the unwanted blue light. These methods can regulate not only the color coordinates but also the color temperature of LEDs, doing no harm to the life span of LEDs.

5. Heat Dissipation
Heat generated by the acting light emitting chip for the LED must be absorbed to maintain normal working temperature without being over-heated and damaged. The industry is striving to develop more efficient heat-dissipating materials.

Although LEDs bear several defects to be improved in the future, they do have many advantages over conventional incandescent lamps. As next-generation light source, offering benefits such as small size, long life span, energy saving and durability, etc., LEDs have aroused great attention among different countries and areas. With the rapid advancement of LED industry all over the world, we believe that the defects of LEDs will be improved in reachable future.