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Semiconductor lighting, often referred to as the third generation of lighting technology, has found widespread application in areas such as large-screen color displays, special lighting, traffic signals, LCD backlights for multimedia devices, and optical communications. As a cold light source, it is environmentally friendly and offers energy efficiency that exceeds 90% compared to traditional incandescent and fluorescent lamps. This makes it a key player in the global shift toward sustainable and efficient illumination solutions.
In the industry, semiconductor lighting is also known as LED (Light Emitting Diode) technology, which encompasses three main components: LED core technology, LED packaging technology, and LED application technology. Over the past few years, with strong government support, LED chip technology has advanced rapidly. The size and power of individual chips have increased significantly, allowing for the development of high-power LEDs, such as 3W installations. Additionally, the design and functionality of packaged LED products have continuously evolved, offering greater flexibility and diversity in lighting applications.
Several countries, including the United States, Japan, and South Korea, have launched national initiatives to promote semiconductor lighting. Major global lighting companies like General Electric, Philips, and Osram have partnered with semiconductor firms to develop new lighting technologies. In the U.S., under the leadership of the Department of Energy and the Optoelectronics Industry Development Association, Sandia National Laboratories began drafting a comprehensive roadmap for semiconductor lighting technology from 2002 to 2020, aiming to set the technical foundation for future lighting innovations.
Japan has also made significant strides in this field through its "21st Century Lighting Project," led by the Japan Research and Development Center of Metals and NEDO (New Energy and Industrial Technology Development Organization). This five-year national initiative involved universities, companies, and associations, with the goal of improving energy efficiency in lighting by up to double that of traditional fluorescent lamps using advanced GaN-based blue and ultraviolet LEDs. The project aimed to reduce energy consumption and carbon emissions, with a total budget of 6 billion yen.
Today, the most widely researched semiconductor lighting technology involves III-nitride LEDs, such as InGaN, AlGaN, and GaN. These diodes emit blue-green, blue, and ultraviolet light, which can be combined with red and green LEDs to produce white light. They can also directly excite phosphors to generate white light, making them ideal for next-generation lighting systems. Nitride LEDs are expected to replace traditional incandescent and fluorescent lamps, becoming the dominant choice in future lighting due to their energy-saving potential and long lifespan.
The luminous efficiency of LED devices has grown tenfold every decade, with GaN-based blue-green LEDs experiencing an even more dramatic increase—over 100 times in just ten years. This breakthrough has enabled full-color LED displays and made white-light LED illumination possible. As material growth and fabrication techniques have improved, LEDs have evolved from low-power indicators to high-power devices capable of driving large-scale applications such as traffic lights, car lighting, and digital billboards.
GaN-based power blue LEDs are considered the third generation of lighting sources, following incandescent and fluorescent lamps. They offer advantages such as high efficiency, long life, compact size, fast response time, durability, and environmental friendliness. These features make them highly promising for various lighting applications around the world.
At the heart of semiconductor lighting is the LED itself. Its working principle involves the recombination of electrons and holes in the active region of a pn junction under forward bias, converting electrical energy into light. Since the 1950s, LED wavelengths have expanded from infrared to visible and ultraviolet ranges. The wavelength of an LED is determined by the bandgap energy of the semiconductor material used. Gallium nitride-based materials, such as AIN, InN, and GaN, are direct bandgap semiconductors that cover a wide range of the spectrum, from visible to deep ultraviolet.
There are three primary methods to achieve white light in semiconductor lighting:
1. **RGB LED Mixing**: White light is created by combining red, green, and blue LEDs. This method allows for precise control over the color temperature and can produce an ideal white light spectrum. However, it requires complex driver circuits and high-performance LEDs, making it suitable for high-end applications.
2. **UV LED Phosphor Excitation**: Ultraviolet LEDs are used to excite trichromatic phosphors, which then emit white light. While promising, this approach currently faces challenges due to the lack of high-power UV LEDs and reliable phosphors.
3. **Blue LED Phosphor Excitation**: This is the most commonly used method today, where blue LEDs excite yellow phosphors to create white light. It offers high lumen efficiency and is widely adopted, despite a slightly lower color rendering index.
Each method has its own advantages and limitations, and the choice depends on the specific requirements of the lighting application. Unless otherwise specified, most discussions about semiconductor lighting refer to the blue LED and phosphor excitation technique.