We probably wonder just how this little bead of acrylic smaller than a pea manages to radiate a visible beam of very intense light in many different colors of the spectrum. We must first categorize its placement in our lighting world.
Each Led uses a solid state technology in order to perform its feat. The color is dependent on the materials used. Some use GaAlAs(GaliumAluminumArsenide as junctured material. Some use a InGaAlP(IndiumGaliumAluminumPhosphor) combination. These are generally much more efficient than the former, though the specifics are not important for the moment.
Figure 1 shows the basics, but Led configurations are wide and varied. All that is required to power any given Led is a means to limit the current flow through that given lamp. This is accomplished using a simple resistor of proper value and power rating for any given design. In Fig.1 near bottom is schematic of LED circuit showing R1 connected to Anode of typical LED. For the sake of simplicity, if 10 volts is applied at point B and the LED shown drops a voltage of 2.0 volts @20 ma., then the value of R1 will be 400 Ohms. Of course, a common and standard value of 390 Ohms would be used. The power rating of the resistor R1 would be .160 Watts. 1/4 Watt would be used(Next higher standard value). At these current values, the life expectancy of the LED would be over 10 yrs. (at least 30+ times that of the widely used
incandescent light bulb).
Figure 2 shows how more than one Led can be used in the original single Led circuit of Figure 1 by just placing them in series and changing the value of resistor R1. Since we know that the current flowing through R1 will be the same, i.e. 20 ma., because LED1 and LED2 are in series, we can calculate the value of R1. Applying 10 volts at point B again, resistor Ri calculates out to be 300 Ohms. Here we can use 330 Ohms, another more readily available standard value. The power rating for R1 in this case again would be a 1/4 Watt value, since it would consume only .120 Watts. We are using 5mm Leds in the examples above, but Led diameters can varry from 2mm…or less to more than 10mm. The opperating designs currents are usually 20 ma. in general, though many of the more recent Led designs are set at 70 ma. and higher. These higher nominal
operating currents are due mainly from newer Led junction design. The Led itself would consume only .04 Watts, i.e., 40 milli-watts, a very small power consumption for a light bulb. Some of the more robust Leds on the market today are available in 1 Watt, 2 Watt, 3 Watt, 5 Watt and even higher. Of course, the package design is forever changing to accomodate this increase in power. The Led efficiency, the amount of lumens in light output per Watt consumed is increasing at a much greater pace than other lighting technologies to where it is hoped to reach 150 lumens/Watt by the year 2012. The incandescent is about 15 lumens/Watt and does not see any increase in the near future.