One trouble – led light sources are still too expensive. But talk about it below. Sure, the led sign everyone – those red and green lights, indicators that apply to any household appliances. But before recently, LEDs were thin and could not be lit in blue and white. Both problems were solved in 1990, and since then we can speak seriously about replacing traditional light sources ultraluminous LEDs. Now is the time to understand how the led, and why he is so good. In fact, it is the same semiconductor diode that is used in electrical circuits as a rectifier, but it is made not from silicon, and from special, so-called "direct-gap" semiconductors.
In general, the semiconductor can be imagined graphically as a two-storey house for electrons. Upper floor (called "conduction band") almost empty. The ground floor ("valence"), by contrast, is filled with e-mail to a refusal, but it may be free space (such "vacant positions" for the electrons in a scientific way are called holes). When an electron with a "top- floor "found a hole, ie, unoccupied space on the" ground floor ", then it becomes possible to" jump down "- a process known as recombination of electrons and holes. If the diode voltage is applied the correct polarity (Light-emitting diodes: from 2 to 4 V, depending on color), the electrons and holes will run towards each other and the recombination will occur in droves. Jumping from the "upper" floors on the "bottom", the electrons lose energy, this energy can be dissipated as heat (as occurs in silicon diodes), and may radiate in the form of light – and the latter is the principle of the LEDs.