LED has long been a new term for the public. We can trace it everywhere: in the morning, when the mobile phone clock rings, the LED has already started working. The LED that provides backlight for the mobile phone screen is LED; when the road tells us when to get off and when to let go of the clutch The red and green traffic lights are LEDs; the elevator floor lights that are pressed out by the office to reach the index finger are also LEDs; after entering the office to turn on the computer, we can start to surf the host and display the indicator light or LED. Now, LED negative The revolutionary task is to replace traditional halogen or fluorescent lamps and become a daily lighting tool.
LED light-emitting principle and electrical characteristics 1.1 LED light-emitting principle A solid-state semiconductor device capable of converting electrical energy into visible light. The most critical component of each LED lamp is a semiconductor "PN" junction, which is formed by a P-type semiconductor and an N-type semiconductor material connected by a certain process. When a proper current is passed through the junction, the electrons in the PN junction The holes recombine and emit energy in the form of photons, such as. The color of the light produced by the LED depends on the material from which the LED is made.
1.2 LED electrical characteristics LED volt-ampere characteristics: LED simple working circuit As shown, the "volt-ampere characteristic" of the LED is the characteristic of the current flowing through the PN junction of the chip as a function of the voltage applied across the PN junction, which is a measure of PN. An important sign of the pros and cons of making a knot. The complete LED "volt-ampere characteristic" contains both positive and negative characteristics.
Like ordinary rectifier diodes, LEDs also have unidirectional conductivity and non-linear characteristics, shown as the "volt-ampere characteristic curve" of the LED.
The LED "volt-ampere characteristic curve" can be divided into three regions of a forward characteristic region, a reverse characteristic region, and a reverse breakdown region.
1 Forward characteristic area: When the applied voltage of the LED is small, since the external electric field is not enough to overcome the resistance caused by the internal electric field to the carrier diffusion motion, the current of the LED is small, and the resistance of the LED is large. When the voltage across the LED exceeds a certain value (this value is usually referred to as the deadband voltage), the internal electric field is greatly weakened, the resistance of the LED becomes small, and the current increases rapidly (see point a in -6).
Is - reverse saturation current (A) q - electron charge, q = 1.602X10-19 k - Boltz constant, k = 1.38X10- / KT a thermodynamic temperature, at room temperature of 25 ° C, 2 reverse Characteristic area: The reverse current is the current that passes through the PN junction when the LED is applied with a reverse voltage. One of its characteristics is that as long as the applied reverse voltage is within a certain range, the reverse current does not substantially change with the reverse voltage (see section 0b). Therefore, the reverse current in this case is often called the reverse saturation current. . The smaller the reverse current, the better the unidirectional conductivity of the LED.
3 Reverse breakdown area: When the reverse voltage of the LED increases to a certain value, the reverse current increases sharply, and reverse breakdown occurs (see point c). This voltage value VB is called reverse breakdown. Voltage. The materials used for LEDs are different and the reverse breakdown voltage is different. As shown, the reverse breakdown voltage of the ALInGaPLED is 20V, while the reverse breakdown voltage of the InGaN LED is only 7V. TCV). AL丨nGaP.LED detection characteristic curve På›4LED actual ä»—-an characteristic curve + ED actual power consumption P is the working current If, that is, P=IfVp. To ensure safe operation of the LED, large allowable power dissipation.
The ED response time means that the response time of the LED lamp through a forward current is an important parameter. The response time of the LED lamp only needs 60 ns, and the white lamp needs 140200 ms to reach the set brightness.
Advantages of LED in Protecting Vision There are four indicators for determining whether a luminaire protects vision: illuminance, illuminance: the degree to which an object is illuminated, expressed in terms of luminous flux per unit area, in lux (Lux, lx), That is lm/m1. Illumination should not be too too, nor should it be too bright. Maintaining proper illumination is good for protecting vision and improving work efficiency. Different places have different requirements for contrast. See Table 1. Table 1. Requirements for different places of control. Study room, office living room bath, room dining, ladder garage, storage illuminance (lx) at night, with illuminance meter at the same level There are great advantages in improving the illumination of the LEDs installed by me.
The illuminance test of the lamp and the ordinary fluorescent lamp office can be used to obtain the illuminance (lx) average value of the LED lamp in the same position on the same plane as the date of the LED lamp and the ordinary fluorescent lamp. June 10 fluorescent lamp (6X40W) June On the 20th, the fluorescent lamp (6X40W) on June 30th, the fluorescent lamp (6X40W) passed the test, and the LED lamp is about 1.3 times of the ordinary fluorescent lamp under the condition that the power consumption is about 1/3 of the fluorescent lamp. Therefore, the use of LED lamps for indoor lighting can better improve the indoor illumination, and protect the vision and improve work efficiency.
Ultraviolet light: Ultraviolet light is a general term for radiation from 10 nm to 400 nm in the electromagnetic spectrum. Ultraviolet rays act on the eye, causing the conjunctiva and cornea, called the illuminating eye, and may also induce cataracts. It can be seen that controlling the ultraviolet intensity of the light source plays an important role in protecting vision. The white light of our daily use lamps has an ultraviolet intensity of 392mW/m2, an energy-saving lamp of 944mW/m2, an eye-protection lamp of 490mW/m2, and an LED of 0mW/m2, that is, no ultraviolet radiation.
Strobe: The frequency at which a light flashes. The reason for the strobe is that the alternating current we use alternates with time, so the traditional luminaire is not always lit, but alternates with alternating current. Flashing too often can cause eyeballs, holes and fatigue and injury. Among the commonly used lamps, the eye lamp strobe is 482 Hz, and the white lamp is 99.9 Hz. It can be known from the principle of LED that the LED lamp works under DC, so the LED lamp does not strobe.
Color: Color is another measure of whether a light protects vision. Since people are active in the sun for a long time, the light from the luminaire is closer to the sun, and the eyes will feel more comfortable. The color rendering index Ra is used to describe the extent to which the light source is close to sunlight. The color rendering index of the eye protection lamp is 70.5, and the color rendering index of the LED lamp is 91.4, which is second only to the white light 99.9. The LED indoor lighting economy is 3.1 than the conventional light source. The luminous efficiency of a more energy-efficient light source is an important indicator of whether a luminaire is energy efficient. The data shows that the efficacy of LED lights can reach 96LM/W, while our commonly used white and ordinary fluorescent lamps are 14.4LM/W and 30LM/W respectively, that is, a 15W LED lamp can emit 1440lm of luminous flux. If you use white light, you need 100W, and ordinary fluorescent light needs 48W. According to the calculation of 6 15W LED lights installed in each office, you can emit 8640lm light flux. If you use ordinary fluorescent light, you need 288W to achieve the same luminous flux. If the electricity bill is calculated at 0.62 yuan / kWh, 4 hours a day, to achieve the same luminous flux, the office electricity cost of the office using LED lights is 81.5 yuan per year, while that of ordinary fluorescent lamps is 260.7 yuan per year. It can be seen that LED lights have great advantages in energy saving.
Some experts have said that "if the national civilian electric lights can be used 50% to switch to LED lighting, the annual electricity savings is the sum of the three Gorges power stations."
3.2 Luminaire Lighting Cost Analysis When selecting a light source, it is scientific and comprehensive to consider the lighting cost. The lighting cost (COL) is the initial (investment) cost of the light source, the energy cost of the light source, and the labor required to replace the new lamp. Cost and other aspects.
Explain the life of the LED lamp. Since the principle of LED illumination is the composite illumination of free electrons and holes when the diode passes through low-voltage DC, unlike traditional lamps that emit light through high temperature or high voltage, the loss during operation will be small. In addition, the LED is completely encapsulated in the epoxy resin, and there is no loose part in the lamp body, so that the LED lamp is shockproof, waterproof and not easily damaged. Based on the above factors, the life of the LED is very high. According to the data, the service life of a single LED is usually up to 510,000 hours. If the life of an LED lamp is 100,000 hours and it is calculated for 4 hours per day, it can be used for nearly 70 years, and almost one new lamp is replaced. Therefore, the cost of replacing the luminaire can be neglected when analyzing the lighting cost of the LED lamp.
First, analyze the lighting costs of using both LED lights and ordinary fluorescent lights in office locations.
Table 3: LED lamp and fluorescent lamp lighting cost in office space Comparison lamp unit price (yuan) annual average electricity fee (yuan) annual replacement lamp cost (yuan) thirteen years lighting cost (yuan) fourteen years lighting cost (yuan) fluorescent lamp (40W The annual average electricity fee is 4h per day, the electricity fee is 0.62 yuan / Table 4 in the station library value room use LED lamp and fluorescent lamp lighting cost comparison lamp unit price (yuan) annual average electricity fee (yuan) annual replacement lamp cost (yuan) two years lighting cost (Yuan) Three-year lighting cost (yuan) Fluorescent lamp (40W) The annual average electricity cost is calculated by burning 12 hours per day and electricity cost 0.62 yuan/(kW.h).
It can be seen from the analysis in Table 3 that the lighting cost of each LED lamp in 14 years is lower than that of the fluorescent lamp, and the saving effect is not obvious.
Further analysis of the lighting costs of using LED lights and ordinary fluorescent lamps in the station library room.
As can be seen from Table 4, in places such as the station library value room where long-term lighting is required, the advantages of LED energy saving and durability will be more obvious. Each set of LEDs can save 87.4 yuan in lighting cost within three years, and the saving effect is more obvious. .
4 points to know that during the use of LED, the electro-optical conversion rate is close to 100%, which can indirectly reduce the emission of exhaust gas such as C2 and S2 in thermal power plants, reduce the pollution to the environment, and there is no extra ultraviolet light in the spectrum, therefore, and other Compared with light sources, LEDs are the most environmentally friendly.
Although the price of LED lamps is very high, the energy cost and maintenance cost are very low for places like long-term lighting such as the library value room. As the price of LEDs continues to decrease, the lighting cost will be much lower. For fluorescent lights.
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