White LED

What Is Led?

LED stands for Light Emitting Diode. An LED is a semiconductor chip that converts electrical energy into light. The conversion of energy into light happens on the quantum level within the molecular makeup of the semiconductor chip. The process begins with the chip acting as a diode with two terminals, a P (Positive hole carrier) and N (Negative electron) region in its basic structure, which allow the chip to conduct in one direction for operation. In addition, there are added chemical layers called epitaxy layers that enhance the ability of the device to emit light (Photons).As electrical energy passes through the P and N regions of the LED, electrons move to higher energy levels called band gap potentials. To meet the conservation of energy law, the electron's excess energy, gained while moving energy levels, will then produce a photon that our eye will perceive as light. At this point, the band gap potentials equal the energy of the photon created when the electron that was moving energy levels comes back to the ground state.

True Efficacy Of Led Lamps

Light sources perform well when used in a suitable environment. The lumens per watt, the SI unit commonly used for measuring the total amount of light emitted by a light source per energy input, does not accurately reflect the true efficacy of LED light sources. An LED is a directional light source and emits little or no spherical light, whereas lumen-per-watt takes into account all light emissions, including spherical, from a light source and not just what is actually accomplishing the required illumination task.

Need for controlling

LEDs have a very steep voltage/current curve.  What this means is if we change the voltage by a small amount the current will change by a large amount.  This also means that LEDs need to be tightly controlled in order to achieve consistent results. LEDs need control circuitry in order to operate safely and efficiently. A sophisticated controller, using a switched-mode power supply will allow us to dim the LEDs to save power, and it will allow you to extract the maximum amount of energy from your battery. At the other end of the scale, we can simply not bother with any sort of current control - you might get away with it.

Reliability of white leds     

            

  The first and greatest contribution of the new white LEDs is their reliability.  These LED bulbs are solid state Light Emitting Diodes and have an expected lifetime of around 100,000 hours.  That's over 11 years of continuous operation.

Abstract

                  Once limited to simple status indicators, light emitting diodes (LEDs) are now widely used in backlighting, panel indication, decorative illumination, emergency lighting, animated signage, etc. LED lights for commercial and residential buildings are also emerged. It was the low light output and a lack of colour options that had limited the use of earlier LEDs. However, new LED materials and improved production processes have resulted in brighter LEDs in colours throughout the visible spectrum with efficacies greater than incandescent lamps. These brighter, more efficient and colourful LEDs are finding more and more lighting applications.

A Switching Regulator

A switching regulator, or switched-mode power supply (SMPS) can be thought of as a 'transformer' that converts one voltage to another with minimal losses. The series-pass transistor of Figure above is replaced by an SMPS module (Figure below) and, again, current feedback serves to maintain the voltage across the diodes at exactly the right point for safe operation.

Led Variations

Speaking of LED variations, it is probably worth taking a few moments to talk about the differences between individual LEDs.  If we make 50 identical parts on the same wafer, all 50 parts will be different.  In fact, we have to test each part to figure out what the part is.  In the case of white LEDs, the voltage curve, the efficiency and the color all vary from one LED to the next.  As a result vendors sort the parts into separate bins and sell them at different prices.  The best LEDs are the most expensive.

Computer control

Computer control may seem to be a bit of a gimmick but, if we do not trust a microprocessor-controlled lamp, then our designs will work without it. But if we do want some additional features, a small 'PIC' processor (from Arizona Microchip) makes it easy to add them.

Conclusion

However, given the remarkable technological innovation of the past few years, it is expected that market expansion will bring further improvements in LED luminous efficiency, and further cost reductions. The range of uses will surely continue to increase, not only for white LEDs but also for LEDs of other colors, within the context of saving energy and the need for thinner designs. The LED, the new "light" of the 21st century, will surely serve as a key technology for social infrastructure, such as traffic systems, as well as many industrial sectors, such as electronics and automobiles.