White LED

Introduction

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 emerging.

Overview

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).

Another recent development of a blue color LED has led to RGB (Red Green Blue) white lighting as well as Phosphor on Blue to form white LEDs. The technique of Phosphor coating on Blue has shown that in the near future, white lighting from solid-state sources is a possibility, which has led to a lot of excitement.

Leds Vs Incandescent Lamps

For many applications, LED lamps are superior to incandescent lamps. Their efficiency is the most apparent in applications requiring colour. Unlike incandescent bulbs that give off the full spectrum of light in a spherical pattern, LEDs emit a focused beam of a single wavelength (colour) in only one direction, in a variety of angles. The composition of the materials in the semiconductor chip determines the wavelength and, therefore, the specific colour of the light. Lenses, reflectors and diffusers can be integrated into the package to achieve the desired spatial radiation characteristics. The beam patterns on the lamps change when we select different diffusers.

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.

Resistor As Current Limiter

The most common way to control LEDs is to add a resistor in series with the LED. The resistor acts to limit the current flow by causing a voltage drop across the resistor. You can use the internal resistance of the batteries themselves and this what is done for all the small flashlights that use 3 alkaline batteries. However, even with well-chosen values, the tolerances are sloppy. The solution is very inexpensive but has the problem of wasting a lot of power in the resistor. Power losses of 15% to 25% are typical.

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.