Ultrabright diode

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  • LED emitt light when they are directly polarized. When the LED conducts, the electrones pass through the N-type material conductive zone to the P-type material conductive zone. Since the semiconductors of theP-type material conductive zone have less energy in contrast to the semiconductors of the N-type material, the energy of the electrons is emitted in the form of light.

    The characteristic of the LED is the same as in ordinary p-n compounds with the difference in the voltage drop in the conductive regime at the large LED (typically 1.2 to 4.3 V). The wavelength of the light emitted depends on the width of the energy gap between the conductive zones of semiconductors of the N and P type.

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    The production of LED rapidly changed during the eighties when the highly efficient GaAlAs and ultrabright InGaAlP LED first appeared. All the primary colors (RGB) were available, now with the same or better reliability than the other technologies. Surface LEDs became available in one-color (including white), two-color (usually red and green), and tricolor forms. These highly efficient and ultrabright LEDs are used as backlighting for LCD panels, panels with different equipment, and in the interior for the LED information scroll boards. LEDs are also used as flashes for the mobile phone cameras.

    Although they look no different then the ordinary monochromatic LEDs, “ultrabright” diodes are characterized by the light emission which can be considered “white light”. (Figure 1) There are two technologies used to get “white light” from the LED. One way is to incorporate the red, green and blue body very close to one another in the same package (Figure 2) so proportional mix of light allows the human eye the sense of “white light”. In the image you can see that the green LEDs are most numerous because in production the green ones are of least quality.

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    In addition to the methods of production, the disadvantage of this solution is the high price. However, these LEDs are popular when the use of LCD panels is concerned because they allow the change of the background color.

    The cheaper approach is consisted of the phosphorus with the blue LED which absorbs a partition of the blue light and emitts secondary colours to the approximately white light. From the light spectrum we can see that the blue color is most common. (Figure 3). Some early white LED constructed with the mentioned procedure were used as lighting in mobile phones.

    By 2000 the ultrabright LEDs had a voltage drop of 4 to 4.2 V in the direct regime. Mobile phone manufacturers had to have a built-in DC-DC converter which would increase the voltage of the 3.6 V lithium batteries so as to enable LEDs to work in mobile phones. White LEDs are now produced with the voltage drop of 3 to 3.1 V, which allows mobile phone manufacturers to use the power for the LEDs directly from the battery.

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    The main reasons for using white ultrabright LEDs for object illumination are:

    • can be powered from a source of 5V
    • have high luminosity (typically over 4000 MCD)
    • low consumption
    • continuous operation of 100 000 hours (11 years)
    • angle of light from 15 to 45 degrees depending on the model
    • the built-in protection from
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