As we all know, the LCD screen light has a life limit, and the life of the backlight of a better industrial LCD screen can reach 50,000 hours, while the life of the backlight of an ordinary LCD screen is 15,000 hours. This backlight life refers to the process in which the backlight of the LCD screen gradually fades when the LCD screen works for 24 hours. There are actually two main factors in the backlighting of LED backlights for LCD displays:
1. The Quality Problems of The LCD LED Light Bar Itself:
① The quality of the LED crystal used is poor, and the brightness decays quickly
② There are some defects in the production process
2. Conditions of Use of The LCD Screen:
① LEDs are driven by constant current, and some LEDs are driven by voltage to attenuate.
② The drive current is greater than the rated drive condition. In fact, there are many reasons for the light decay of the led light bar, the key is the hot star problem. Although many manufacturers do not pay special attention to heat dissipation in secondary products, the degree of light attenuation of these secondary LED products will be higher than that of LED products that pay attention to heat dissipation after long-term use. The thermal resistance of the LED particle itself, the influence of the silver paste, the heat dissipation effect of the substrate, the colloid and the gold wire are all related to the light attenuation. Semiconductor materials have a very interesting property called carriers; there are two types of carriers: electrons, which are negatively charged, and holes, which are positively charged. The light-emitting principle of LCD is that two kinds of carriers can combine under certain conditions, and the released energy emits light in the form of photons. Therefore, according to different materials, the energy levels occupied by electrons and holes are different, that is, the relative energy level difference between electrons and holes determines the combined emission energy level of the two carriers, which can produce Photons of different energies, thereby controlling the wavelength, ie spectrum or color, of the light emitted by the LED. In most applications, LEDs are powered by DC.
It has the following characteristics:
1. Shunt bias characteristics: When the DC has sufficient positive voltage, the current of the LED rises rapidly. This inflowing current is called "shunt bias current", and the voltage across the LED is called "shunt bias voltage". High or low voltage ranges indicate abnormal quality, the shorter the wavelength/kloc-1 the higher the voltage.
2. Reverse bias characteristics: As the name suggests, it is to give LED a negative voltage, also called "leakage voltage". Generally speaking, different LED materials will have their own reasonable voltage values, and the reason for poor reverse voltage characteristics is electrostatic discharge, which can also be used to evaluate the quality of this LED. The main material of LED is pn junction, and thyristor is a commonly used control element in power electronics. When its thickness is uneven, the pn planes will be staggered, and the voltage difference at this time will be very different, which is the "thyristor effect". If the voltage difference is too large, it will indicate that the quality of this product is not very good, so it can also be used to measure LEDs. However, the quality of LEDs is generally not judged by the gate fluid effect, but by testing the VFD of the LED. VFD less than 0.1V is judged as qualified.
