With the development of optoelectronic technology and biological science, artificial light sources are increasingly used in garden landscape lighting. The urban garden lighting landscape is the city's bright business card, with a very impactful visual art and cultural expression. Through the expression and interpretation of the garden lighting language, it not only the sublation, refinement and sublimation of the daytime landscape, but also the beauty of the natural landscape and the human landscape itself, but also the beauty of interpretation, interpretation and emphasis of the lighting language. At the same time, through the garden lighting, the public can also enjoy the garden night scene of “like the sky and the worldâ€, which is of great significance for cultivating the people to love nature, love life and love the cultural connotation and spirit of the city.
In recent years, LED has been developed as a garden landscape lighting source product for urban landscape lighting projects, but there are not many related scientific reports. The author starts with the basic principle of LED, introduces its basic principles and characteristics, and makes forward-looking prospects for the sustainable promotion and application of LED in garden landscape lighting, aiming to provide a reference for the industry to better promote and use LED. .
1 LED basics
The history of light source development is the progress of human civilization. In 1879, the incandescent lamp invented by Edison marked the beginning of the use of electric light source. Its development has experienced incandescent lamp (1879), halogen lamp (1959), high pressure sodium lamp (1961), metal. Halide lamp (1962), the red LED lamp was introduced in 1969, and then LED as a new energy-saving, environmentally friendly green light source product has brought unlimited hope to the 21st century light source market.
LED (Light Emitting Diode) is a special semiconductor that emits light and emits light. It is a semiconductor solid-state light-emitting device. The light source is only used for backlighting of various product displays. With the development of materials and technologies, LEDs can directly emit red, yellow, blue, green, cyan, orange, purple, and white light.
1.1 LED basic principles
The LED uses a solid semiconductor chip as a light-emitting material. When a forward voltage is applied to both ends, carriers in the semiconductor recombine to cause photon emission to generate light. Its luminescence mechanism is that the terminal voltage of the PN junction constitutes a certain barrier. When the forward bias voltage is applied, the barrier decreases, and the majority carriers in the P and N regions diffuse toward each other. Since the electron mobility is much larger than the hole mobility, a large amount of electrons diffuse into the P region, which constitutes injection of minority carriers in the P region. These electrons recombine with the holes on the valence band, and the energy obtained during recombination is released as light energy. This is the principle of PN junction illumination.
1.2 LED light source features
Compared with the ordinary light source, it has many superior features: First, the use of low-voltage Power Supply, the supply voltage is 6 ~ 24V, depending on the product, it is a safer than the use of high-voltage power supply, especially suitable In public places. Second, the energy consumption is small, and the energy consumption is reduced by 80% compared with the incandescent lamp with the same light effect. Third, the color is adjustable, changing the current can change color, and the light-emitting diode can conveniently adjust the energy band structure and band gap of the material through chemical modification method to realize multi-color light emission of red, yellow, green and blue. For example, a red LED with a small current can change to orange, yellow, and finally green as the current increases. Fourth, it is highly adaptable, small in size and light in weight. Each unit LED chip is a square of 3 to 5 mm, so it can be prepared into various shapes and suitable for a variable environment. Fifth, it has good stability and long service life. 100,000 h, the light decay is the initial 50%. Sixth, the response time is short, and the response time of the incandescent lamp is millisecond. The response time of the LED lamp is in the order of nanoseconds. Seven is low-carbon and environmentally friendly, with little pollution to the environment, and the product has no harmful metal mercury.
1.3 LED basic characteristics
1.3.1 LED electrical characteristics
The brightness of the LED is proportional to the current through the LED, ie the greater the current flowing through the LED over its current limit parameter, the higher its luminance. However, green light, blue light and white light will saturate under high current conditions, which not only greatly reduces the luminous efficiency, but also shortens the service life.
1.3.2 LED optical characteristics
The optical characteristics of LEDs are mainly considered from several indicators: first, luminous intensity, second, total luminous flux, third, spectral characteristics, chromaticity coordinates, dominant wavelength, fourth, spatial distribution of luminous intensity and total luminous flux, and fifth, luminous intensity. LEDs provide monochromatic light with a large half-width. Since the energy gap of a semiconductor decreases with increasing temperature, the peak wavelength emitted by it increases with temperature. The LED luminance L is approximately proportional to the forward current. As the current increases, the luminance of the light also increases approximately. In addition, the luminance of the light is also related to the ambient temperature. When the ambient temperature is high, the composite efficiency is lowered and the luminous intensity is decreased.