Two common methods utilized in LED illumination to achieve power conservation may include LED pulse driving and driver circuit multiplexing. It is also common to use both methods in conjunction with each other. Multiplexing simplifies overall circuitry and reduces the component count by strategically grouping the LED light anodes and cathodes together. Pulse driving delivers a series of short electrical pulses to illuminate the light emitting diode or array. To calculate desired power consumption, the engineer must first determine the duty cycle. To calculate duty cycle, simply divide the pulse width, or amount of time the LED illuminates, by the period, or the amount of time between pulses. The result conveniently expressed as a percentile, indicates how much power the LED lamp will consume while pulsed at this duty cycle. Consider a pulse width of 0.001 second and a period of 0.01 second. When divided, we get a duty cycle equial to 0.1 or 10%. At this duty cycle, the LEDs will consume only 10% of the power they normally would consume.
Power conservation techniques permit functionality while consuming less energy and providing continuous operation in battery operated or automotive applications. Many battery operated LED designs can benefit from this specialized circuitry. In simple terms, power conservation means that the LEDs will continue to operate, but consume only a small fraction of the power they normally would require. Benefits include extended battery life as well as decreased heat dissipation. As a disadvantage, the LED array may appear much dimmer than normal. For this reason, power conservation circuitry is not always a feasible solution in all LED lighting applications. LED indicator applications are the most common type of application to utilize this technology. Consider LED indicator lamps designed to provide human feedback about the status of an electrical system. When the system becomes active, the LED indicator lamps would turn off. When not in use, the LED illuminates as an indication or warning that operation has discontinued. If the device relied on a battery for power, and remained inoperative for several months, the LED would require sufficient power to illuminate over this period. This is an ideal scenario where power conservation circuitry can preserve battery life while providing LED illumination for an extended period.
The LED offers efficiency on many levels ranging from cost to power. With the proper circuitry and design, an LED array can operate at a higher than normal efficiency for special applications where constant operation is ideal. This concept takes advantage of the non-liner relationship between forward current and luminous output. Light emitting diode datasheet graphical data depicts how an LED can operate more efficiently at lower power settings. For example, an LED operating at 20 mA might provide a luminous output of 100%. The same LED can operate at half power, 10 mA, but provides a luminous output of 70%. This non-linear relationship demonstrates that a 50% reduction in power does not necessary result in a 50% reduction in luminous output. The same LED indicator lamps may be capable of operating at only 5 mA but may continue to produce a luminous output near 50%. Some applications do not always require 100% luminous output, and could benefit by operating at much lower power settings.
Digital lighting systems contain at least two general states, on and off. Appling the concept of power conservation allows a "partially on" state to substitute the off state. In other words, the LED illumination appears on or partially on, but never off. This function primarily serves as a form of continuous indicator lighting, in most LED applications. When LED indicator lamps operate at an extremely conservative power setting, they can usually continue to provide enough luminous output for basic visibility purposes. However, the extremely low drive current does not produce significant heat dissipation or cause battery depletion in battery operated lighting devices. One example of an LED device equipped with this dual functionality is the automotive taillight cluster equipped with special parking mode. In most vehicles, the taillights are inoperative while the vehicle is not in use. However, the LED taillights offer a constant marker mode by allowing a drastic reduction in forward drive current to only several milli-amperes. The LED taillight cluster will remain in the partially on state but will not draw enough current to deplete battery levels. This feature can serve primarily as a parking indicator to increase visibility of the parked vehicle. The safety feature can alert passing drivers while engaged in roadside parking situations.
A function requiring even less power can often increase visibility dramatically. As opposed to a state of steady operation, a pulsating LED array can remains on or partially on for only a fraction of a second. This function is extremely beneficial in battery dependant applications that require continuous operation. LED indicator lamps operating in strobe function consume much less power when compared to a state of continuous LED operation. Unlike traditional lighting systems, LEDs do not suffer from degradation due to a constant switching routine. The lifespan of an incandescent light bulb may suffer dramatically if the operation consisted of a continuous strobe or flash routine. The exact opposite is true with LED technology. Applying a pulsed signal to the LED will actually increase the overall LED lifespan. During strobe routines, a dramatic heat reduction promotes an extended LED lifespan. The strobe function is also very convenient for LED taillight applications equipped with a special parking mode.