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The Development of Semiconductor LED Lighting Fixtures (2)
Sep 21,2012
Future Technology Development Trends of LED
LEDs are compact, lightweight, operate at low driving voltage, provide full color, have a long lifespan, high efficiency, are vibration-resistant, and are easy to control light, which offers excellent conditions for designing lighting systems for different places and purposes. People are accustomed to seeing things in sunlight, and for general lighting, the main requirement is a light source that closely resembles sunlight quality, so white LEDs are an important indicator of semiconductor lighting technology. Due to the low power and brightness of a single LED, it is not suitable for standalone use, thus multiple LEDs must be assembled together to design a practical LED lighting system. However, there is still a certain distance between white LEDs and the requirements for general lighting, and many technical and cost issues urgently need to be resolved.
Main Technical Overview of Semiconductor Lighting Fixture Systems
1) Heat Management of Fixture Systems
LEDs are generally referred to as cold light sources because the principle of LED light emission is that electrons recombine to directly emit photons without the need for a heating process. However, due to the presence of Joule heating, LEDs also generate heat while emitting light, and in high-power and multiple LED applications, the accumulated heat cannot be underestimated. Unlike traditional lighting sources such as incandescent lamps and fluorescent lamps, excessive temperatures can shorten or even terminate the lifespan of LEDs. Moreover, LEDs are temperature-sensitive devices; as the temperature rises, their efficiency drops sharply. Therefore, system structure design and heat dissipation technology development are also challenges that LED applications must face. Since forced air cooling is generally undesirable in light sources, as the input electrical power increases, heat sinks and other methods to enhance natural convection cooling play an increasingly important role in LED lamp and light source design.
2) Improving Color Rendering
Currently, white LEDs commonly use blue light LEDs combined with yellow light-emitting YAG phosphors excited by blue light to produce white light. Since their emission spectrum only contains blue and yellow wavelengths, there are issues with high color temperature and low color rendering index, which do not meet general lighting requirements. The human eye is much more sensitive to color differences than to light intensity, so for lighting, the color rendering of the light source is often more important than luminous efficiency. Therefore, adding an appropriate amount of red-emitting phosphors while maintaining high luminous efficiency is an important topic in LED white light illumination.
3) Secondary Optical Design of Fixture Systems
Traditional fixtures have long used incandescent and fluorescent light sources as reference points to determine the optical and shape standards of fixtures. Therefore, LED fixture systems should consider abandoning the assembly method of traditional fixtures combined with LED light-emitting modules, fully taking into account their optical characteristics, and designing different fixtures specifically for LED light sources. The design content of the optical system mainly includes the following aspects: ① Determine the shape of the optical system, the number of LEDs, and the power size based on the lighting object and light flux requirements; ② Combine several LED light tubes to design point light sources, ring light sources, or surface light sources as "secondary light sources" and calculate the lighting optical system based on the combined secondary light sources; ③ The light distribution control of each LED tube on the "secondary light source" that constitutes the lighting optical system design is very important.
Since the light beam emitted by LEDs is concentrated and easier to control, and does not require reflectors for focusing, it helps reduce the depth of fixtures. For example, using a planar mirror optical system, only 1-2 LEDs can illuminate a large surface while keeping the fixture depth very thin; using light guide technology, LEDs can be directly mounted next to light guide tubes, greatly reducing the volume occupied by the light source and other components, resulting in ultra-thin fixtures.
The above content is organized and reproduced by Nanjing Tansuo Optoelectronics www.njtansuo.com
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