LED Technology

The LED Lighting Revolution

Evolving light-emitting diode (LED) technology is enabling brand new uses for LEDs. See how they've gone from simple indicator lights to illumination.

Most typical LEDs are designed to operate with no more than 30 to 60 mW of electrical power. This is because the first LEDs were inefficient light emitters, so the first applications were as indicator lights, not as illuminating lights. And billions of LED lamps are still used as indicators. Just look around your office or home and you'll find dozens.

Around 1999, Lumileds introduced power LEDs capable of continuous use at one watt. These LEDs used much larger semiconductor chip sizes to handle the larger power inputs. The semiconductor chips were mounted onto metal slugs to allow for heat removal that is created at the LED chip junction.

These "power LEDs" began an explosive technology leap towards establishing the LED lighting revolution. One of the key advantages of LED-based lighting is its high efficiency, as measured by its light output per unit of power input (lumens per watt, or lm/W). White LEDs (RGB types) quickly matched and overtook the efficiency of standard incandescent lighting systems. In 2002, Lumileds made five-watt LEDs available with a luminous efficacy of 18 to 22 lumens per watt. A conventional 60 to 100 watt incandescent light bulb produces around 15 lm/W, and standard fluorescent lights produce up to 100 lm/W.

In September 2003, a new type of blue LED was demonstrated by Cree, Inc. to provide 24 mW at 20 mA. The addition of a special phosphor coating produced a packaged white light giving 65 lumens per watt at 20 mA, becoming the brightest white LED commercially available at the time, and more than four times as efficient as a standard incandescent bulb. In 2006, Cree demonstrated a prototype with a record white LED luminous efficacy of 131 lm/W at 20 mA. The highest efficiency high-power white LED is claimed by Philips Lumileds with a luminous efficacy of 115 lm/W at 350 mA, pulling this LED even with standard fluorescent lights.

Seoul Semiconductor has plans for 135 lm/W by 2007 and 145 lm/W by 2008, which would be approaching an order of magnitude improvement over standard incandescent and better even than standard fluorescents. Nichia Corp. has developed a white light LED with luminous efficacy of 150 lm/W at a forward current of 20 mA.

High-power (> 1 W) LEDs are necessary for practical general lighting applications. Typical operating currents for these devices begin at 350 mA.

Why LEDs Make Better Lights

Longest Life

First off, LED lamps last much longer than incandescent, fluorescent or halide lamps. After 11 continuous years of use, the LED is still working, although the light output would typically be at 50 percent of its starting light output. The incandescent will typically fail catastrophically after three months of continuous use and the fluorescent will fail catastrophically after 35 months of continuous operation.

The long life of the LED means it can be designed into a lamp without concern for replacement as the LED will outlive nearly any application it will go into. This reduces — or even eliminates — maintenance costs associated with re-lamping or replacing bulbs.

Most Efficient Light Source

Secondly, LEDs emit light in a half-spherical pattern as opposed to incandescent bulbs, which emit light in a full-spherical pattern — much of the incandescent's light is therefore lost before it gets to the target. Adding a lens (light director) to an LED changes the light pattern so that it is focused on the target.

As seen in the Cree diagrams, the fixture efficacy of the LED (including driving and heat losses) is 72 percent better than the incandescent and 24 percent better than the compact fluorescent lamp (CFL). And the LED starts out with four to five times the lumens/watt of the incandescent. The LED lighting solution provides over 5X higher in-fixture light efficacy than the incandescent and over 50 percent better than the CFL.

Most Environmentally Friendly Light Source

The LED light will consume less than 10 watts of power compared to the 60 watts for the incandescent for the same light output. As 29 percent of the total electric power consumed in the United States is for lighting, LEDs offer a dramatic way to reduce our nation's power consumption.

In addition, unlike other light sources, LEDs contain no mercury and emit no ultraviolet rays or infrared heat.

Converting High-Efficiency, High-Power LEDs Into Solid State Lighting Products

The LED itself is the key ingredient to building a solid state light, but the advantages of the LED will be lost if the design is not done properly. Properly means that the following design issues are managed with a high degree of engineering skill: thermal management, lens design, and electrical driving.

Thermal Management

The heat created in the LED must be transferred out of the LED into a heat sink and then to the ambient as efficiently as possible. The path the heat follows must provide the lowest possible resistance. (The resistance is measured in °C/watt.) Creating the lowest value resistance path from the LED junction to the ambient at an economic cost is a challenging task that requires considerable engineering knowledge and creativity.

Lens Design

The goal of lens design is to maximize the number of photons emitted from the LED chip to be directed at the target area (the area the light is to illuminate). There are a wide variety of approaches to designing a lens system. A lens can be complicated or simple, expensive or cheap. Understanding the trade-offs in lens performance versus cost is critical to designing the most cost-effective system. Efficient lens systems allow the light to use fewer LEDs and therefore less power, but the cost of the lens system needs to relate to the reduction in LEDs and power consumption.

Electrical Driving

LEDs are light emitting diodes and they need to be driven as diodes. This means they must be driven by constant current sources. High-power LEDs typically operate at quite low voltages, 3-4 volts. And, they operate most efficiently when they are driven by DC (direct current). Today nearly all lighting systems are driven by power from the mains at 110-120 V_AC (alternating current). There is a growing number of applications for landscape lighting that are driven at 12 V_AC by the utilization of a transformer that takes the mains down to 12 V_AC. Adapting LED lighting modules to the available driving systems requires special circuits between the mains and the LED. These circuits will in many cases be designed for an individual LED light and incorporated in the module. In other applications, the LED lights may be driven from power supplies that are connected to multiple LED lights. Efficient, well-engineered driving circuits are critical to LED lighting performance, reliability and cost.

OptoElectronix Turns LED Components Into LED Lighting Modules

With expert skills in these three key areas, thermal management, lens design, and electrical driving, OptoElectronix is uniquely positioned to design and manufacture modules that incorporate all areas — these modules are today known as light engines.

Light engines are LED modules designed for specific LED lighting applications. They are the "bulbs," ready to drop into a lighting fixture and go to work.

But the LED "bulbs" are tailored to the lighting application and optimized for cost efficiency for that application. Because many lighting applications are very similar, OptoElectronix offers standard light engines. For lighting applications that are unique, we also offer custom light engines.