Ultra-bright led is a new type of led whose brightness is nearly 100 times higher than the general led led. Its shell is colorless transparent resin package, and its emitting body itself can emit a certain wavelength of light, thus presenting a certain color. Ultra-bright led is widely used in outdoor billboards, electronic displays, traffic lights, signs, car taillights, LCD backlight, etc.
Compared with traditional lighting, ultra-bright led has the following advantages: 1) long life, reliable and durable, very low maintenance cost. Led can be used continuously for 105h, which is 100 times longer than ordinary incandescent bulb. 2) the high efficiency can reach 201m/w. It is expected to reach 501m/w by 2005. The spectrum of led is almost entirely concentrated in the visible frequency band. Its luminous efficiency can reach 80% ~ 90%. 3) bright, light color pure 12-inch red traffic lights, for example, it USES a low of 140 w incandescent lamp as light source, light efficiency of 2000 lm Bai Guangjing red filter, optical loss of 90%, only 2001 m of red light, and in lumileds lighting company USES 18 red lamp, led light source design, including circuit loss, only 14 w power consumption, can have the same luminous efficacy; 4) lighting fast car signal light is an important field of led light source application. Due to the fast response speed of led (ns class), the installation of high level led brake light on the car can reduce the occurrence of rear-end collision accidents. In recent years, high-lit leds have been used in near-light lighting in cars, such as audi a86.o of Germany, the yak concept car introduced by fioravanti of Italy at the 2003 Geneva auto show, and the model u introduced by ford of the United States at the Detroit auto show. Although ultra-bright led has many advantages, it still has the following disadvantages at present: 1) the power of single led in the market is generally below 5w, and there is no more high-power led, which is the biggest bottleneck for led to become the first choice of lighting. 2) need to strictly control the temperature of the led is a semiconductor material, as well as ordinary diode has a p-n junction, due to highlight the power of diode is relatively large, so the same as the power semiconductor devices, the need to consider the heat dissipation problem, junction temperature is too high will directly affect the service life of the led, and increases the led light failure, severe cases will led burn out; 3) high price in addition to low power, price is the main factor that makes it difficult for led to become lighting. Although led has been recognized by most people and is well regarded by most people, its high price is difficult to be accepted by consumers. At present, single yellow led is about o. 6 yuan/piece, green and blue single led in 1. About 8 yuan per led, the price of white led reaches 2.2 ~ 5.5 yuan per led; If dozens of single leds are combined, the cost will increase greatly. For example, if an led is installed in a lawn lamp, its unit price will be several times that of a general lawn lamp. In order to become the mainstream lighting source in the future, led must develop towards the direction of great lumens, so that the cost may be reduced and the market may break through.
Hpwa-xh00 is an ultra-bright led by lumileds lighting company. This paper takes it as an example to analyze the characteristics of ultra-bright led. FIG. 1 shows the relationship curve between forward voltage drop (vf) and forward current (if). It can be seen from the curve that when the forward voltage exceeds a certain threshold value (about 2v), that is, the commonly said conducting voltage, it can be approximately considered that if is proportional to vf. Table 1 shows the current electrical characteristics of the main ultra-bright leds. As can be seen from table 1, the highest if of ultra-bright led can reach 1a, while vf is usually 3 ~ 4v. As led light characteristics are usually described as a function of current, not a function of voltage, luminous flux (phi v) and if relationship curve is shown in figure 2, therefore, the use of constant current source drive can better control the brightness. In addition, it can be seen from table 1 that the range of positive pressure drop of led is relatively large (the maximum can be more than 1v). As can be seen from the vf-if curve in figure 1, a small change of vf will cause a large change, and if will cause a large change in brightness. Therefore, the constant voltage source drive can not guarantee the led brightness consistency, and affect the led reliability, life and light decay. Therefore, ultra-bright leds are usually driven by constant current sources. FIG. 3 is hpwa-xh00 led temperature and luminous flux (phi v) relation curve, as shown in FIG. 3, luminous flux and temperature are inversely proportional, the luminous flux at 85℃ is half of 25℃, and the time output at 40℃ is 1 of 25℃. Eight times. The change of temperature also has a certain influence on the wavelength of LFD. Therefore, good heat dissipation is the guarantee of constant brightness of led.