LED光源控制技术

Light-emitting diodes (LEDs) used for illumination are solid-state devices that produce light by passing electric current across layers of semiconductor chips that are housed in a reflector, which in turn is encased in an epoxy lens. The semiconductor material determines the wavelength and subsequent color of the light. The lens converts the LED into a multidirectional or unidirectional light source based on specification.

Traditionally used since the 1970s for indicators and numeric displays, colored LED technology has recently made inroads into a range of mainstream applications such as exit signs, traffic lights, task lights, accent lights, wall washing, signage, decorative lighting, display lighting, cove lights and other tight spaces, wall sconces, outdoor lighting, automobile lights, downlighting and custom lighting.

LEDs offer a number of benefits vs. traditional light sources, including small size, which increases flexibility with fixture designs and ability to light tight spaces; greater reliability, with no filaments or moving parts; greater energy efficiency, with 70 percent less energy being consumed; safer and environmentally friendly operation, with less waste and no mercury; color-changing; and increased quality, color and strength of light.

“LEDs are already an important technology because of their advantages -- life, controllability, both spatial and temporal, and the ability to create rugged, unique fixtures,” says Dr. Nadarajah Narendran, Director of Research, Lighting Research Center, Rensselaer Polytechnic Institute. Researchers like Dr. Narendran have been studying LEDs and promoting their technological development for years.

“While they still have limitations compared with the traditional light sources that everyone is used to seeing, LEDs are the latest rage in the illumination world because of their tremendous flexibility and potential for innovative solutions,” says Dr. Makarand “Chips” Chipalkatti, director of OSRAM North American LED Lamp Modules.

Colored LEDs currently dominate the exit sign market, are making inroads into the traffic signal market (with current penetration estimated at 15-20%), show significant promise for automobile lighting, and are being sold in a variety of consumer products such as flashlights and light wands. In commercial applications, colored LEDs, which can be combined in custom arrays, can also be controlled to produce dynamic color-changing effects for contour lighting, wall washing, accent lighting, signage, advertising, display, public space and “architainment” applications.
“With LEDs, colors can be dynamically controlled,” says Narendran. “For example, a dawn to dusk scene can be created in an office space, if needed. Similar scenes can be created for night shift workers. Quantus Airlines already has such a system in some of their aircraft.”

The first white light LED was developed in the mid 1990s, a blue indium gallium nitride (InGaN) LED with a phosphor that converts some of the light output into yellow, producing a cool, bluish-white light with a color temperature ranging from 4000K to 11000K. White light can also be produced by combining red, blue and green LEDs in an array, or using an LED that produces UV light that is converted into white light by an RGB phosphor, similar to a fluorescent lamp. Suitable applications include cove lighting, display lighting and undershelf lighting. To address the demands of illumination applications, LEDs have evolved to larger sizes and wattages, now including 3W and 5W units in addition to 1W, and with heat-sinking materials to dissipate heat and extend useful life. White LEDs have generated a lot of excitement as they continue to evolve towards a competitive alternative to popular general light sources.

Unfortunately, white LED technology is still too immature for prime time in many major general lighting applications due to light output, cost and color stability issues. While LEDs are approaching the light output of some low-wattage incandescent lamps (see Table 1) and becoming more efficacious (20-24 LPW for LEDs vs. 16 LPW for incandescent), the current cost per kilolumen is about $200 versus $0.40 for incandescent. However, experts such as Dr. Narendran predict that these roadblocks will be overcome within five to 10 years, including predictions that efficacy will reach 160 LPW and cost per thousand lumens will fall to $2.

“The popularity of LEDs will grow rapidly as scientists are able to make them brighter, while emitting a consistent white light,” says Dr. Chipalkatti of OSRAM.

Table 1. LED Light Output. Source: LightingResearchCenter, 2003

These predictions are believable when one considers the intensive research effort going into the LED technology race by such as organizations as the U.S. Department of Energy and partnerships between lamp and semiconductor companies, who are used to thinking in terms of six-month product cycles. In fact, by the time you read this article, the labs may already be raising the bar with new discoveries. LED light output, for example, has doubled every 18-24 months since 1970.

As the roadblocks are overcome, the lighting industry may experience a complete transformation in the future. Besides doubling the efficiency of standard lighting systems, the small size of LEDs provides new possibilities in fixture sizes and shapes, as well as color-changing. A related technology, organic LEDs (OLEDs), offers the possibilities of using “lighting wallpaper” cut to specification. OLEDs can also be integrated into architectural and room materials -- imagine a curtain by day that becomes a light source by night.

No other technology than LEDs and OLEDs, called “solid-state lighting” as a family, has such high energy-savings potential. Solid-state lighting has the potential to save enough energy to power the states of Arizona, Colorado and Mississippi and reduce the nation’s electric bill by nearly $100 billion over the next 20 years.

“It is becoming clear that LED technology will be key to the progress of lighting in coming years,” says Alan Marble, marketing manager for LED drivers for Advance Transformer.

Until that time, LEDs will continue to be used in thousands of applications around the world, already providing much of the lighting used in applications such as retail stores, casinos, museums, houses of worship, bridges, public spaces, restaurants and bars, hotels, building facades and other spaces. LEDs are being adopted because of the captivating color-changing effects they offer in addition to advertising claims of long service life. Fixture manufacturers are also beginning to incorporate LEDs into new designs either as a distinguishing accent or as a primary light source.

Perhaps the most dramatic contribution of LEDs to lighting so far, however, has actually not been the displacement of standard light sources, but the development of entirely new applications and creative possibilities.

Manufacturers of LEDs include Cree, Lumileds, Nichia and OSRAM Opto Semiconductors. Manufacturers of LED lighting systems include Color Kinetics, GELcore, Lumileds and OSRAM Opto Semiconductors. Manufacturers of LED drivers include Advance Transformer, Color Kinetics, Maxim, Microsemi, OSRAM SYLVANIA/OSRAM Opto Semiconductors, Rohm and Toshiba.

Although LED technology has made significant advances in recent years, relatively, its applications are not widespread. The Alliance for Solid-State Illumination Systems and Technologies (ASSIST) is working towards overcoming hurdles and identifying suitable applications for LED technology. ASSIST is a program formed by the LightingResearchCenter in collaboration with leading manufacturers and system benefit administration groups. OSRAM Opto Semiconductors, Gelcore, Nichia, Boeing Aircraft Co., the New York State Energy Research and Development Authority, and the California Energy Commission have currently signed up for the ASSIST program. (For more information about ASSIST, visit http://www.aboutlightingcontrols.org/click.php?url=www.lrc.rpi.edu/programs/solidstate/ASSISTHome.htm.)

Table 2.  Capabilities, advantages and things to
watch out for when choosing LED lighting products.

Dimming & Control

LEDs are low-voltage light sources. Individual LEDs used for illumination require 2-4V of direct current (DC) power and several hundred mA of current. As LEDs are connected in series in an array, higher voltage will be required. Changes in voltage can produce a disproportional change in current, which in turn can cause light output to vary. If current exceeds the manufacturer recommendations, the LED’s useful life can be shortened.

An LED lighting system consists of a power source, LED driver and the LEDs. The driver functions similarly to a fluorescent or HID ballast in that it regulates the current flowing through the LED. Some drivers are manufactured to operate specific LED devices or arrays, while others can operate most commonly available LEDs. Drivers can be dimmable and/or enable sequencing.

LEDs are easily dimmed by reduction in the forward current, pulse width modulation (PWM) via digital control, or more sophisticated methods. For PWM, the frequency must be as high as hundreds of thousands of modulations per second so that the LED appears to be continuously lighted without flicker. PWM is more popular.

LED lighting systems are easily integrated with circuits to control dimming and color change so as to enable the creation of intelligent lighting that responds to occupant presence or commands.

Color Changing. The color output of LED arrays can be controlled using a driver/module that enables sequencing. The sequencing module generates a preset sequence of colors, with the specifier able to control the speed of each sequence. Each LED in an LED lighting system can be individually controlled and programmed by interfacing with DMX digital controller, enabling thousands of LEDs to dynamically dim up or down to create a seemingly infinite spectrum of colors.

Dimming. LEDs can be dimmed over a wide range of light output, from 100 percent to less than five percent. Dimming does not result in a loss of efficiency. Dimming requires an LED dimming driver.

LED lighting systems with designated drivers can be integrated with any traditional 0-10V control device or system such as occupancy sensors, photocells, wallbox dimmers, remote controls, architectural and theatrical controls, and building automation and lighting control systems. LEDs can also work with the digital addressable lighting interface (DALI) protocol and in the future, may include wireless (RF) as a control option.

Lamp life is not affected by dimming, as is sometimes the case with frequently dimmed fluorescent lighting. In fact, dimming LEDs might even lengthen the useful life of LEDs, because dimming lowers operating temperatures inside the light source.

Dimming causes LEDs to experience a similar shift in spectral power distribution as an incandescent lamp, according to the LightingResearchCenter. However, if colored LEDs in an array are used to produce white light, the amount of shift, particularly higher with red and yellow LEDs, may produce an undesirable effect on the white light we are trying to produce.

LED Drivers and Systems

Advance Transformer. Advance announced the introduction of its Xitanium LED Driver Line in 2002. Xitanium drivers can support a wide variety of LED-driver applications, including general illumination and sign lighting as well as a variety of new construction and niche applications such as architectural and outdoor lighting, undercabinet lighting and retail display. All Xitanium products are backed by a five-year warranty.

According to Advance, Xitanium drivers are the industry’s first product line of LED power supplies designed specifically for lighting applications. All Xitanium units are designed for maximum versatility and will work with LEDs from any manufacturer. “We’ve designed Xitanium drivers to provide maximum flexibility to lighting designers,” says Marble, “giving them the freedom they need to fulfill the potential of this exciting new lighting technology and fully utilize the benefits of LEDs as a light source.”

A key feature of the Xitanium line is the compact size and light weight of the drivers, allowing them to be easily and unobtrusively incorporated in LED designs. The modular nature of the power package design gives designers versatility, permitting them to tailor drivers to specific application requirements. Each driver is rated for a 50,000-hour life, matching the rating for LEDs. Since these drivers are UL Class 2 and FCC Class B rated, they can be used in a variety of locations, with no special wiring routing requirements. A damp location option is available. Xitanium drivers are capable of operation at temperatures as low as minus 40oC, matching the low temperature at which LEDs themselves can operate, and as high as 60oC.

See Advance’s Xitanium line by clicking here:
http://www.aboutlightingcontrols.org/click.php?url=www.advancetransformer.com/xitanium/advance/products.html

Use Advance’s product selector to find the right driver for the application by clicking here:
http://www.aboutlightingcontrols.org/click.php?url=www.advancetransformer.com/xitanium/

advance/find_your_driver/find_your_driver_main.html

OSRAM. OSRAM Opto Semiconductors has announced the launch of its new LINEARlight Colormix LED dimmable lighting system. The system utilizes the new LINEARlight Colormix module in conjunction with the OPTOTRONIC LED power supply, OPTOTRONIC OTDIM electronically stabilized dimming module, and the powerful OSRAM LINEARlight Optic lens. All of the system building blocks can also be used individually for a variety of lighting applications.

The LINEARlight Colormix module provides dynamic control of colored illumination through the use of three chips inside each LED, with a viewing angle of 120° per LED. Each module (450mm) consists of 30 surface-mounted LEDs that can be subdivided into smaller units of LEDs, and can be expanded to include as many as 10 modules with one feed-in unit. The units generate little heat during continuous operation. These dynamic and flexible features enable the systems to be used in a widening range of large scale applications, including edge lighting, either transparent or diffused glass, illuminating facades and coves, and a number of other architectural features.
The LINEARlight Colormix LED Dimmable System utilizes:

? OSRAM OPTOTRONIC? LED power supply. Compact and electronically stabilized, the unit provides a wide range of input voltage from 100 to 240 VAC on single-phase AC power lines. Supplies are available in 10Vdc and 24VDC outputs and are protected against open and short circuiting, overloading and overheating. They are UL recognized and FCC compliant.

? OPTOTRONIC? OTDIM. This is a compact, electronically stabilized dimming module with a nominal output power of 50-watts at 10 VDCand 120-watts at 24 VDC. The unit provides for open and short circuiting, overloading and overheating protection. It is ideal for use in color mixing applications with LINEARlight Colormix as well as all other OSRAM LED modules.

? OSRAM LINEARlight Optic lens. This lens offers high optical efficiency and increases light intensity by reducing the viewing angle from 120° to 20° (colored LEDs) and 25° (white LEDs), effectively creating a uniformly illuminated, low profile, light strip.

“This new dynamic color control and dimming capability continues to expand current applications for LED-based lighting,” says Dr. Chipalkatti. “With this system and its building blocks, there are new opportunities to apply LED technology to escape route markers, border markers, stair markers, backlighting and many more.”

OSRAM SYLVANIA has also announced a series of LED lighting systems that include power supplies, LED modules and connectors. LED modules are often used for effect lighting, providing new accents in architecture. Effect lights bring color to gray facades, columns can be highlighted and strong signal effects can be produced. Marker lights are the ideal solution for marking walkways, steps, seating, and can be used in a wide range of applications in orientation and information lighting.

OSRAM SYLVANIA's Backlights are the building blocks for highly versatile backlight LED solutions for commercial signage. They can be separated into small units ready for installation. A unique innovation relates to the options in flexible modules that can adapt to contours of various 3-D surfaces and are also self-adhesive.

OSRAM SYLVANIA’s OT RGB control modules are compact PWM controllers for creating colored lighting solutions with LEDs. The OT RGB 3CH DIM allows color mixing by independently controlling three dimmable output channels. The OT RGB SEQUENCER generates a preset dynamic sequence of colors, allowing the user to control the speed of the sequence. Both modules are controlled by 0-10VDC control inputs.

To view OSRAM SYLVANIA’s LED power supplies and modules, click the link below, then in the lefthand column, click “Product Catalogs” until you see the product lines, which will include LED products.