(ORDO NEWS) — Once upon a time there was a boy who was well versed in how the world works: he could, for example, tell why the sky is blue, how a helicopter flies, and where a cat got kittens from. He also knew how the LED lamp works. Inside it, the boy said, is a crystal, on different halves of which there are many charge carriers: on the one hand, electrons, and on the other, holes (conventional particles, with which physicists denote the absence of an electron).
Electrons and holes are attracted to each other, therefore, a “wall” of electrons is formed at the interface on one side, and holes on the other. The boundary between them is called the electron-hole, or pn-junction.
When a voltage is applied to such a crystal, electrons and holes disappear, leaving behind only light (this process is called carrier recombination). As long as the current flows and the charge carriers recombine and emit light, the light is on.
Unlike an incandescent lamp, an LED lamp in theory only shines, but does not heat: this is the nature of the pn junction. It is believed that LED lamps do not heat up more than 40 – 70 degrees. The boy who knew everything in the world, and knew it like the back of his hand. Therefore, I decided to gently touch the LED light with these very fingers …
But he left out one thing. The electron-hole junction really emits only light, but the semiconductor crystal itself also heats up, and quite strongly – sometimes up to 125 – 150 degrees. It is heated by the internal resistance of the semiconductor crystal through which the current runs.
If the diode is small, the heat goes away through the contacts that connect the crystal to the current source. It is more difficult with large diodes: heat from them must be additionally diverted to an air radiator, the role of which can be played by any piece of iron.
The mounting plate with the crystal is placed on the radiator, as a rule, with the help of heat-conducting glue. The quality of the heat sink directly affects the temperature of the diode lamp: if the glue is bad, there is little of it, or it is unevenly distributed over the plate, the heat of the crystal will go not to the radiator, but into the air, and heat the lens under which the crystal is hidden – that is, in fact, the light bulb.
By pressing your fingers to an object that is even heated to 100 degrees, you can easily get a painful burn. Our boy was lucky, his burns were gone in just two days. Now he looks with disbelief even at those household appliances about which he knows a lot. Because theory is theory, and practice is a completely different matter.
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