The customs will conduct spot checks on the import and export goods of SMD LED, conduct cross testing on the import and export goods of SMD LED, and conduct black and white testing on the import and export of SMD LED. There are 19 locations in China.
What are the working principles of light emitting diodes? Light emitting diodes are made of III-IV group compounds, such as GaAs (arsenide tube), GaP (phosphide), GaAsP (phosphorus arsenide tube) and other semiconductors, and their core is the PN junction. Therefore, it has the I-N characteristics of a general P-N junction, namely forward conduction, reverse cutoff, and breakdown characteristics. In addition, under certain conditions, it also has luminescent properties. Under forward voltage, electrons are injected into the P region from the N region, and holes are injected into the N region from the P region. A portion of the minority carriers (minority carriers) entering the other region combine with the majority carriers (multi carriers) to emit light, as shown in Figure 1.
When purchasing a new LED bead, attention should be paid to the following points: 1. When the power is turned on, the LED emits an alarm light under the forward current. A small number of charge carriers (minority carriers) will be triggered by different conditions of electronic vibration, causing rapid breakdown under the forward current and causing an electrical effect. When the capacitance is weak or prosperous under the action of an electric field, the operating frequency will decrease significantly. Under the action of an electric field, the composite power density will sharply decrease, Instead of high-frequency maps.
According to the characteristics of the light emitting surface of the light emitting tube, it can be divided into circular lamps, square lamps, rectangular lamps, surface light emitting tubes, lateral tubes, surface mounted microtubes, etc.
Circular lights are divided into diameters φ 2mm φ 44mm φ 5mm φ 8mm φ 10mm and φ 20mm, etc. Foreign countries usually φ 3mm LED labeled T-1; hold φ 5mm is denoted as T-1 (3/4); hold φ The 44mm mark is T-1 (1/4). The angular distribution of circular luminous intensity can be estimated from the size of the half value angle. There are three categories based on the angular distribution of luminous intensity.
● High directionality. Generally, it is a pointed epoxy packaging or a packaging with a metal reflection cavity, without adding a scattering agent. The half value angle is 5 ° -20 ° or less, which has high directionality and can be used as a local lighting source or combined with a light detector to form an automatic detection system.
● Scattering type. This is an indicator light with a larger viewing angle, with a half value angle of 45 °~90 ° or greater, and a larger amount of scattering agent