Conventional LEDs have been used for indication and display applications for several decades. The inherent benefits of LED technology are well-known and documented, and include, maintenance and power savings, as well as performance features that are taken for granted by electronics-savvy consumers such as durability, reliability, longer life span, and consistent color and brightness levels. These benefits, combined with society’s growing environmental concerns and subsequent demand for green, energy-efficient products, have continued to drive the development of LEDs for challenging new industries and markets, such as general illumination for commercial and residential buildings. With the escalating demand for solid-state lighting, LED manufacturers are motivated to develop high-lumen LEDs while LED lighting companies are working hard to integrate the latest technology into retrofit packages and luminaries. However, new perspectives may be necessary for people to adopt LED technology as an illumination source in new installations, or incorporate LED technology in existing light fixtures.
Are LEDs suitable for commercial and residential lighting applications?
LEDs are arguably the most energy-efficient light source available. Case in point, LEDs have created upwards of 80 percent energy savings in the traffic signal industry. However, in this application, the LEDs had two natural advantages:
1. LEDs are monochromatic, so almost all of the light generated is used. In contrast, the white light generated by an incandescent bulb needs to transmit through a colored filter. Light outside of the frequency of the colored lens is wasted.
2. LEDs are directional, so almost all of the light generated was emitted towards the lens. In contrast, light from an incandescent bulb needed to be reflected toward the lens, resulting in loss of efficiency.
Commercial and residential lighting applications stand to gain similar, if not more, energy-savings by converting to LEDs. However, most applications are not as straight-forward as stuffing a PC board with a bunch of directional red, amber or green LEDs. LED light fixtures and retrofit packages have to be designed to distribute the directional light generated by the LED over wide areas. Moreover, white LED technology, while continuously improving, does not yet have the optical color and brightness that consumers have become accustomed to with incandescent lights. However, the power savings can be significant, for example, in California the energy commission has adopted efficiency standards for residential and commercial buildings. These standards, Title 24, have accelerated development of LED illumination technology.
Why LEDs are not in your house?
Unlike incandescent bulbs, high-power LEDs cannot be simply plugged into a wall socket . Several companies are working to overcome the technological and economic challenges by developing LED light fixtures and retrofit LED lighting products using high-power LEDs. Thermal management, complex drive circuitry, optics, and packaging are challenging hurdles for developers to contend with. There are also educational barriers to overcome in the development of commercial LED illumination products. Getting users to adopt new types of fixtures, understand the illumination characteristics of LEDs, choose the appropriate viewing angle for a given application, select the appropriate intensity for a given application, and understand the limitations of LED color temperatures are pivotal to developing the market for LED technology in commercial and residential lighting.
For the past couple of centuries, traditional luminaries have consisted of a light bulb and lamp socket that enables consumers to continually replace bulbs that have burned out. Whether it is an incandescent, compact fluorescent or fluorescent light bulb, it will simply screw or drop into an industry-standard socket and the luminary will continue to be operational. A few LED lighting companies have developed high-flux LED bulbs that retrofit into existing sockets ; but this approach is less than ideal. For example, a traditional light bulb socket provides a very poor thermal path for cooling an LED light source. Incandescent light bulbs are basically heaters that produces visible light, and the socket it is screwed into is designed to protect the lamp base and wiring from that heat. With high-power LEDs, most of the wattage consumed is converted to heat and, if it can’t be dissipated through the lamp socket , will dramatically shorten the LED life.
Complex Drive Circuitry
To protect the LED from degradation factors, such as heat and voltage spikes, the drive circuitry design is critical. Ideally, LED circuit designs should be tailored to the specifics of the application because mechanical and economic constraints make it difficult to design a “catch-all” circuit. Most LED indication or lighting designs operate from a high voltage AC power source. Since LEDs are DC-driven, utilizing a specific AC to DC power supply to achieve a DC source voltage is often the most cost-efficient and reliable LED lighting solution. To ensure efficient LED operation, DC-to-DC LED driver circuitry may also be required in conjunction with the primary power supply. In addition to providing the necessary power and protection from current fluctuations, LED drive circuitry also generates heat – adding to the thermal management challenge. And, generally, the greater the volume of light that is required, the more LEDs are needed, leading to more complex the circuitry, packaging challenges, higher heat flux, etc.
Optics: Illumination Angle
LEDs are extremely energy-efficient from an illumination efficacy standpoint, i.e., lumens per watt. Upwards of 95 percent of the light can be directed at the target area of illumination whereas a typical incandescent bulb may be only 60 percent effective. In other words, a lot of the light produced by an incandescent bulb does not go to the intended target. Incandescent bulbs require reflectors, louvers, and/or diffusers to compensate for unnecessary light. Fluorescent bulbs are more energy-efficient than incandescents, but the ballast may consume up to 20 percent of the electrical energy going into the fixture. Retrofitting LED technology in traditional luminaries is tricky because most fixtures are designed to overcome the limitations of traditional spherical light output. Reflectors, cones, masks, shades and diffusers help bend, redirect, or shield the light emitted from incandescent, fluorescent and halogen sources, but it creates unnecessary physical barriers for implementing LED technology. Designing specific forward-fit LED-based luminaries can produce several times foot-candles on a given area per watt than other traditional incandescent bulb technologies. Because of the directional illumination pattern that LEDs provide the light can be directed to the specific area that needs to be illuminated.
Optics: Light Color
Over the years, fluorescent bulb manufacturers had some challenges getting users to accept the white color produced by fluorescent technology. Because of the limitations of phosphor technology, the fluorescent industry introduced subjective terms such as “cool white” or “warm white” to draw comparisons to incandescent white. Not coincidentally, white LED manufacturers face the same challenges since white LED technology is based on phosphor energy. To put things in quantitative perspective, LED manufactures have referred to Color Rendering Index (CRI) which is a measurement of a light source’s ability to render colors accurately. The higher the CRI, the more natural the colors appear, with natural sunlight having a CRI of 100. However, this may not be the best metric for comparing light sources. Originally developed in 1964, this index is based on color models with broad spectral distributions. White LEDs are narrow-band sources. Color Temperature may be a more suitable tool for comparison because it is a less subjective measure, based on degrees Kelvin. Presently there are several white emitters to choose from in the 3,200 degree-Kelvin and 5,500 degree-Kelving range. No matter how the color is measured, LED manufactures have made great strides to match the warm white glow of an incandescent bulb with high-quality LEDs due to the tremendous demand for incandescent white tones.
Users have come to understand the brightness of incandescent and fluorescent light bulbs in terms of watts; however a watt is technically the unit of electrical power used by the lamp during its operation. Consumers know from experience how much light a 40, 60, or 100 watt light bulb will produce. The same cannot be said for LED assemblies, as LED lamps are generally designed to meet the specific targeted illumination requirements of a given application. For example, it is possible to compare an LED equivalent to a 50 watt MR16 bulb as this type of lamp is used as a directional light source. However, a typical 60 watt incandescent bulb produces a spherical light pattern. An LED lamp that could provide equivalent light in all directions would be tricky to design in the same mechanical envelope. With present technology, multiple LED emitters and/or secondary optics would be required to achieve a 360-degree illumination pattern.
But the bigger issue is, the light intensity benchmark for an LED lamp is not the watt. Traditional LEDs used for simple status indication and displays come in small epoxy packages and their light output is measured in candelas because this is a measurement of direct-view luminous intensity. With the recent development of high-power LEDs for illumination purposes, the lux or lumen (one lux is equal to one lumen per square meter) is a more suitable unit of measurement to compare the LED light output to traditional sources because we are more concerned about the volume of light rather than the directional intensity.
These terms are certainly known in the LED and lighting industry, but not by the general commercial and residential consumer. And the question is how willing is the consumer to learn new terminology and understand their lighting needs?
High quality monochromatic LEDs can provide 70% of their original lumen output at 100,000 hours if designed properly. White LEDs degrade faster because the degradation rate of the phosphor, but if properly thermally-managed, can provide upwards of 50,000 hours of operation. In addition, experienced LED lighting designers understand how electrical or thermal deficiencies in the overall solid-state light design can cause catastrophic failure or accelerated degradation and develop robust designs accordingly.
Market demand will continue to drive understanding, and ultimately, standardization of LED form factors for commercial and residential lighting. Adopting application-specific solid-state designs will enable LED designers to provide customers with green benefits and a redefinition of maintenance standards that are measured in years rather than hours. It is only a matter of time.