Principle of the LED
An LED is an abbreviation for light emitting bond, or "light emitting diode" in Chinese.
Unlike conventional incandescent, fluorescent and HID lamps, leds emit light in the form of a direct conversion from electricity to light.
From the discovery of this luminous phenomenon in 1907 to the development of blue LED needed for mixing white light in 1993, gradually attention has been paid to the use of light sources.
In recent years, with the improvement and development of technology, the white LED which achieves the same luminous efficiency has also come into use.
LED type and structure
LED luminescence principle is basically the same, but can be divided into:
1) cannonball LED
The cannonball structure is made by sealing the LED chip in the reflection cup of the lead holder, then sealing the resin mixed with phosphor powder, and finally forming by curing the resin.
2) surface patch type LED
An LED chip is inserted into a ceramic or resin molded base plate model and then sealed with a curing resin or silicone resin mixed with phosphor powder.
3) Chip on Board(COB)
The construction of multiple LED chips directly encapsulated on the substrate.
LED was first reported in 1907 as a solid substance that glows through an electric current, but was initially used only as an indicator.
In 1993, with the invention of blue light LED, the three primary color R, G and B light sources of LED were developed accordingly.
In 1996, yellow phosphor was added to blue LED to realize white LED.
Since then, through continuous technical improvement, an era of LED energy-saving lighting is coming.
Characteristics of the LED
Compared with traditional light source, LED has various characteristics, among which the biggest one is long life.
In addition, the LED chip is small and easy to control light, so the volume of lamps can be made very small, which can design lamps that cannot be designed before.
The LED is easy to start up without preheating.
Leds contain little radiation other than visible light and are suitable for lighting objects sensitive to heat and objects sensitive to ultraviolet light.
The existing light source is poor in shock resistance and impact resistance due to the use of glass lamp bodies.
Because the LED does not use glass tube, there is no risk of breakage. It is a reliable and safe lamp.
LED does not contain heavy metals such as mercury and chromium in fluorescent lamp, metal halide lamp, and does not pollute the environment.
The way white leds glow
1) combination of blue light LED and yellow phosphor
The three ways below are the most efficient.
The LED emits blue light and stimulates the phosphor to emit yellow light.
The deficiency of this method mainly lies in the relative shortage of red spectrum, but it has been improved continuously in recent years.
Toshiba products are mainly made in this way.
2) mixing of common primary colors (RGB)
Due to the lack of continuous distribution of the spectrum, the white light obtained by mixing the three primary colors will have an unnatural feeling when irradiating the object.
Therefore, it is generally not used in the lighting application of objects. It is mainly used in the display screen that directly sees the light source and the large image device.
3) the RGB phosphor is excited by ultraviolet LED
Similar to the general fluorescence of fluorescent tubes, high quality white light can be obtained, but the luminous efficiency is inadequate.
The life of the LED
As the LED is a solid light source, there is no problem of extinguishing due to the broken filament of the traditional light source.
However, due to the aging of materials used, the luminous flux will slowly decrease with the increase of lighting time.
LED life, according to the technical data of 134 white LED lighting lamps performance requirements formulated by Japan lighting equipment industry association in July 2005, "the LED life in the light source of general lighting lamps is 70% of the luminous flux and 70% of the time from the luminous intensity to the starting luminous intensity".
Toshiba conformed to this, using a unique evaluation technique to represent a life span of up to 70 per cent of the starting luminous flux.
The LED light color
LED is produced through the complex and sophisticated semiconductor manufacturing process, so the luminous flux and wavelength of the product in the current situation will have a certain range of fluctuation deviation due to the manufacturing process.
Furthermore, white LED is generated by mixing phosphors, and factors such as differences in coating amount of phosphors will result in poor consistency compared with traditional light sources.
Therefore, the product has deviation in light color and brightness because of different chip production and packaging time.
The published values of the catalog products such as luminous flux, color temperature and light distribution do not represent the guaranteed values, so a certain deviation should be considered.
Efficiency of LED lamps
When considering the economic efficiency of lighting lamps, not only the efficiency of light source, but also the electrical efficiency and optical efficiency of lighting lamps must be considered comprehensively.
LED is compared with all kinds of lamps with traditional light source, so comprehensive efficiency should be considered.
The heat of the LED lamp
Leds emit almost no infrared rays that emit heat, but they generate heat from themselves, lamps and power point lights.
The heat dissipation efficiency has a great influence on LED life.
So the installation and use of the product needs to refer to the specific product conditions in advance.