Q1: What is the difference between the lumen efficiency of a single LED and that of a lamp made of LED lights?
A: For a specific LED, there is a defined forward bias, such as IF=20mA forward current (corresponding VF ≈ 3.4V), and the measured radiation flux φ = 1.2lm, then the lumen effect of LED is η = 1.2LM × 1000/3.4V × 20mA = 1200/68≈17.6LM/W。 Obviously, for a single LED, for example, the applied electric power Pe=VF × IF, then the measured radiation flux at this power will be converted into lumens per watt, which is the lumen effect of a single LED.
However, as a lamp, no matter the power VF on the LEDPN junction in reality × What is IF? The electric power of the lamp is always the input port of the lamp. It includes the power consumption of the power supply department (such as voltage regulator, voltage stabilizer, AC rectifier to DC power supply department, etc.). The presence of a drive circuit in the lamp will cause its lumen efficiency to be lower than that of the single LED being tested. The greater the circuit consumption, the lower the lumen effect, so it is extremely important to find an efficient LED driver circuit.
Q2: What is the LED junction temperature? What effect does high junction temperature have on LED?
A: The LED base structure is a semiconductor PN junction. When the current flows through the LED device, the PN junction temperature will rise. Strictly speaking, the temperature of PN junction area is defined as the junction temperature of LED. Generally, because the device chip is very small, we can also take the LED chip temperature as the junction temperature. LED wall washing lamp price
When the PN junction temperature (such as shell temperature) increases, the ionization of impurities in the PN junction accelerates, and the intrinsic excitation accelerates. When the concentration of composite carriers generated by intrinsic excitation is much higher than the concentration of impurities, with the decrease of migration rate, the influence of the increase of the number of intrinsic carriers is more serious than that of the semiconductor resistivity transition, leading to internal quantum effect. The increase of temperature leads to the decrease of resistivity, leading to the decrease of VF under the same intermediate frequency conditions. The LED driven by IF constant current source has not been eliminated. The decrease of VF will increase the IF index. This process will double the LEDPN junction temperature, and eventually the temperature rise will span the large junction temperature, leading to the LEDPN off effect. This is a positive feedback malignant process. Price of outdoor wall washing lamp
The rise of temperature on the PN junction makes the photon emission process of the excited electron/hole recombination reaction in the semiconductor PN junction degenerate from the high energy level to the low energy level. This is because when the temperature on the PN junction increases, the amplitude of the semiconductor lattice increases, thus increasing the vibration energy. When the necessary value is exceeded, the electron/hole will exchange energy with the lattice atom (or ion), and transition from the excited state to the ground state, thus becoming a transition without photon radiation, and the optical function of the LED will decline.
In addition, the PN junction temperature can also trigger the ionization of impurities in the semiconductor impurity ions of the lattice field, causing the horizontal fission of ions, which tends to be stable under the influence of the PN junction temperature, which means that the lattice vibration changes its lattice symmetry, trigger energy levels, and electronic transition spectrum due to the influence of temperature, which is why the wavelength of LED light changes with the rise of the PN junction temperature.
In conclusion, the temperature rise of the LEN PN junction will lead to the transformation of its electrical, optical and thermal functions. Excessive temperature rise will also change the physical properties of LED packaging materials (such as epoxy resin, phosphor, etc.), leading to LED failure. Therefore, reducing the temperature rise of PN junction is the key point to use LED.
Q3: What is electrostatic comminution? What type of LED is easy to be damaged by static electricity and cause failure?
A: Electrostatic electricity is actually composed of charge accumulation. In daily life, especially in a dry climate, people will feel "electric shock" when touching doors and windows, which is the "discharge" of static electricity accumulated in doors and windows to a certain extent. For wool fabrics and nylon chemical fiber products, the static electricity accumulation voltage can be as high as 10000 volts. The voltage is very high, but the static electricity power is not large, which will not threaten life, but even life. However, some electronic equipment will cause the equipment to decline.