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>> LED TECHNICAL INFORMATION CENTER

  • Advantages of LED Lighting over conventional lighting
  • Led Color
  • C.I.E. 1931 Chromaticity Diagram
  • Leds Applications
  • Future-"smart LED lighting" Power wireless networks
  • Future-OLED
  • Advantages of LED Lighting over conventional lighting
LEDs offer numerous benefits due to their mode of operation:

Energy Efficiency
LEDs are highly efficient. In traffic signal lights, a strong market for LEDs, a red traffic signal head that contains 196 LEDs draws 10W versus its incandescent counterpart that draws 150W. Various estimates of potential energy savings range from 82% to 93%. With the red signal operating about 50% of the day, the complete traffic signal unit is estimated to save 35-40%. It is estimated that replacing incandescent lamps in all of Americas some 260,000 traffic signals (red, green and yellow) could reduce energy consumption by nearly 2.5 billion kWh. At the end of 1997, more than 150,000 signals were retrofitted, almost all of them red.

In architectural applications, the greatest penetration of LEDs has been in exit signs, both new signs and retrofits. LED retrofit products, which come in various forms including light bars, panels and screw in LED lamps, typically draw 2-5W per sign, resulting in significant savings versus incandescent lamps with the bonus benefit of much longer life, which in turn reduces maintenance requirements. Some of these products are designed specifically for either on-face or two-face exit signs. Many new LED exit signs are also available, including edge-lit designs. LED products currently make up about 50% of the exit sign market. A study conducted by the Lighting Research Center in 1998 found that about 80% of new exit signs being sold in the U.S. utilize LEDs. Note that most retrofits are restricted to use in stencil-type signs versus panel-type signs.

Long Life
Some LEDs are projected to produce a long service life of about 100,000 hours. For this reason LEDs are ideal for hard-to-reach/maintain fixtures such as exit sign lighting and, combined with its durability, pathway lighting. This service life can be affected by the application and environmental factors, including heat and if being overdriven by the power supply.

Range of Colors
LEDs are available in a range of colors (see above), including white light. White light can also be produced through color mixing of red, blue and green LEDs. In addition, through the innovative combination of various-colored LEDs, dramatic color-changing effects can be produced from a single fixture through dynamic activation of various sets of LEDs. Manufacturers such as Color Kinetics offer fixtures that employ this principle. Color Kinetics offers track, theatrical, underwater, outdoor and other fixtures utilizing variable-intensity LEDs that can provide more than 16.7 million colors, including white light. These fixtures can be individually controlled via a PC, DMX controller or proprietary controller to generate effects including fixed color, color washing, cross fading, random color changing, strobing and variable strobing.

Dr. Nadarajah Narendran of the Lighting Research Center is doing some exciting research on the use of colored LEDs in retail display lighting. Preliminary research suggests that using colored LED background lighting combined with spot lighting on merchandise may improve energy efficiency and reduce maintenance costs while catching the eye of the consumer in a fresh manner.

No UV Emissions/Little Infrared
LEDs produce no UV radiation and little heat, making them ideal for illuminating objects, such as works of art, that are sensitive to UV light.

Durable
LEDs are highly rugged. They feature no filament that can be damaged due to shock and vibrations. They are subject to heat, however, and being overdriven by the power supply.

Small Size/Design Flexibility
A single LED is very small and produces little light overall. However, this weakness is actually its strength. LEDs can be combined in any shape to produce desired lumen packages as the design goals and economics permit. In addition, LEDs can be considered miniature light fixtures; distribution of light can be controlled by the LEDs epoxy lens, simplifying the construction of architectural fixtures designed to utilize LEDs. A controller can be connected to an LED fixture to selectively dim individual LEDs, resulting in the dynamic control of distribution, light output and color. Finally, DC power enables the unit to be easily adaptable to different power supplies.

Other Benefits
The other benefits of LEDs include:
  • Lights instantly
  • Can be easily dimmed
  • Silent operation
  • Low-voltage power supply (increased safety)
     Ó Lighting Design Lab
  • Led Color
A. Visible Color
LEDs are highly monochromatic, emitting a pure color in a narrow frequency range. The color emitted from an LED is identified by peak wavelength (lpk) and measured in nanometers (nm ).
Peak wavelength is a function of the LED chip material. Although process variations are 10 NM, the 565 to 600 NM wavelength spectral region is where the sensitivity level of the human eye is highest. Therefore, it is easier to perceive color variations in yellow and amber LEDs than other colors.

LEDs are made from gallium-based crystals that contain one or more additional materials such as phosphorous to produce a distinct color. Different LED chip technologies emit light in specific regions of the visible light spectrum and produce different intensity levels.

  Infrared LEDs
Wavelength (nm)
Color
Color Example
100-280
UV-C

280-320
UV-B

320-395
UV-A

395-430
Violet

430-450
Indigo

450-480
Blue

480-520
Blue-Green

520-555
Green

555-585
Yellow-Green

585-600
Yellow

600-615
Amber

615-625
Orange

625-640
Orange-Red

640-700
Red

700-770
Shortwave NIR

770-1100
Longwave NIR

>=1100
Infrared

The infrared band can be divided into Near Infrared (NIR) and Far Infrared (IR). Far infrared is the thermal infrared used to detect hot objects or see heat leaks in buildings, and is way beyond the range of LEDs. (NIR can be further divided into two bands, longwave and shortwave NIR, based on how film and CCD cameras react, which I'll get into elsewhere, elsewhen, and elsewhy.)
Infrared LEDs are sometimes called IREDs (Infra Red Emitting Diodes).
Ultraviolet LEDs
Ultraviolet light is divided into three bands: UV-A, which is fairly innocuous; UV-B, which causes sunburns; and UV-C, which kills things. Most UV-B and all UV-C from the sun is filtered out by the ozone layer, so we get very little of it naturally. LEDs emit UV-A.

400 nm is a pretty common wavelength for UV LEDs. This is right on the border between the violet and ultraviolet, so a significant portion of the light emitted is visible. For this reason 400 nm UV LEDs are sometimes rated in millicandela, even though as much as half of their energy is invisible. LEDs with lower wavelengths, such as 380nm, are usually not rated in millicandela, but in milliwatts.
 
Eye Protection
LEDs are very bright. DO NOT look directly into the LED light!! The light can be intense enough to injure human eyes.
B. White Light
When light from all parts of the visible spectrum overlap one another, the additive mixture of colors appears white. However, the eye does not require a mixture of all the colors of the spectrum to perceive white light. Primary colors from the upper, middle, and lower parts of the spectrum (red, green, and blue), when combined, appear white. To achieve this combination with LEDs requires a sophisticated electro-optical design to control the blend and diffusion of colors. Variations in LED color and intensity further complicate this process.

Presently it is possible to produce white light with a single LED using a phosphor layer (Yttrium Aluminum Garnet) on the surface of a blue (Gallium Nitride) chip. Although this technology produces various hues, white LEDs may be appropriate to illuminate opaque lenses or backlight legends. However, using colored LEDs to illuminate similarly colored lenses produces better visibility and overall appearance.


White light is a mixture of all the colors. Color Temperature is a measure of the relative amounts of red or blue - higher color temperatures have more blue. 

Color
Temperature Example 
2000K Gaslight 
2470K 15 watt incandescent bulb 
2565K 60 watt incandescent bulb 
2665K 100 watt incandescent bulb 
2755K 500 watt incandescent bulb 
2900K 500 watt Krypton bulb 
3100K Projector type filament bulb 
3250K Photo Flood 
3400K Halogen 
3900K Carbon arc 
4200K Moonlight 
4700K Industrial smog 
5100K Hazy weather 
5500K Sun 30° above horizon 
6100K Sun 50° above horizon 
6700K Electronic Flash 
7400K Overcast sky 
8300K Foggy weather 
30,000K Blue sky 

Remember that this is a measure of color, not brightness, so don't freak out because moonlight is "hotter" than a carbon arc! It just means that the color is bluer, that's all. 
White LEDs have a color temperature, but monochromatic LEDs do not. 
FDS
Intensity
LED light output varies with the type of chip, encapsulation, efficiency of individual wafer lots and other variables. Several LED manufacturers use terms such as "super-bright," and "ultra-bright" to describe LED intensity. Such terminology is entirely subjective, as there is no industry standard for LED brightness.
The amount of light emitted from an LED is quantified by a single point, on-axis luminous intensity value (Iv). LED intensity is specified in terms of millicandela (mcd). This on-axis measurement is not comparable to mean spherical candlepower (MSCP) values used to quantify the light produced by incandescent lamps.
Luminous intensity is roughly proportional to the amount of current (If) supplied to the LED. The greater the current, the higher the intensity. Of course, there are design limits. Generally, LEDs are designed to operate at 20 milliamps (mA).
However, operating current must be reduced relative to the amount of heat in the application. For example, 6-chip LEDs produce more heat than single-chip LEDs. 6-chip LEDs incorporate multiple wire bonds and junction points that are affected more by thermal stress than single-chip LEDs. Similarly, LEDs designed to operate at higher design voltages are subject to greater heat. LEDs are designed to provide long-life operation because of optimal design currents considering heat dissipation and other degradation factors.
 
  • C.I.E. 1931 Chromaticity Diagram

Chart is provided for an understanding of color relationships. RGB monitors and printed materials cannot reproduce the full gamut of the color spectrum as perceived in human vision. The color areas shown only depict rough categories and are not precise statements of color.

C.I.E

C.I.E
Resources from LEDtronics, Inc. &  Andrew T. Young
 
  • Leds Applications
Leds are the next generation of lighting, they could be used ANYWHERE!


With millions of existing products on the market, and more on the way each day, chances are LEDs are used in almost everyone. From indication lights, computer components, watches, medical devices, tanning equipment, the list goes on and on.

Sign Applications With LEDs
Full Color Video, Monochrome Message Boards, Traffic/VMS, Transportation - Passenger Information

Illumination With LEDs
Architectural Lighting, Signage (Channel Letters), Machine Vision, Retail Displays, Emergency Lighting (Exit Signs), Neon and bulb Replacement, Flashlights, Accent Lighting - Pathways, Marker Lights

Signal Application With LEDs
Traffic, Rail, Aviation, Tower Lights, Runway Lights, Emergency/Police Vehicle Lighting

Automotive Applications With LEDs
Instrument Panels & Switches, Courtesy Lighting, CHMSL, Rear Stop/Turn/Tai, Retrofits, New Turn/Tail/Marker Lights

Consumer Electronics & General Indication
Household appliances, VCR/ DVD/ Stereo/Audio/Video devices, Toys/Games Instrumentation, Security Equipment, Switches

Mobile Applications With LEDs
Mobile Phone, PDA's, Digital Cameras, Lap Tops, General Backlighting

Photo Sensor Applications With LEDs
Medical Instrumentation, Bar Code Readers, Color & Money Sensors, Encoders, Optical Switches, Fiber Optic Communication, View Application Detail, Click Here

  • Future-"smart LED lighting" Power wireless networks
October 7th, 2008

Future wireless networks could be powered by "smart LED lighting"
Posted by Sean Portnoy @ 6:17 am

Tags: Network, Light-emitting Diode, Wireless Networking, Wireless Network, Smart Lighting Engineering Research Center..., Wi-Fi, Wireless, Networking, Sean Portnoy


A light bulb went off in the head of researchers at Boston University about a new wireless networking technology, which was very appropriate considering that it involves, well, light bulbs. The Smart Lighting Engineering Research Center has been created to develop technology that would allow low-powered LED lights to transmit data to other devices.

FUTURE LEDS

Such a network could be a boon for home automation, since you could just replace existing lighting with new LED bulbs instead of having to outfit your house with new communications equipment. There are a couple of caveats, though, that mean this network will not be replacing your radio-based Wi-Fi one for many duties. For one thing, because light can not travel through walls and other obstacles, its range is extremely limited. Its throughput is also limited by todays standards, offering data rates between 1Mbps and 10Mbps, or what roughly what 802.11b networks can pump out.

And do not go tossing out your light bulbs just yet. According to the center, this new networking technology probably will not be available for another 10 years.

 
  • Future-OLED
OLEDs
Organic light-emitting diodes (OLEDs) represent another emerging technology that is still in the laboratory. If it can be made practical, it may make even more of a dramatic impact on how spaces are lighted than LEDs. In fact, it may one day replacing LEDs as an energy-efficient alternative for general lighting.

OLEDs are similar to electroluminescent lighting, in which a sheet of material is excited so that it emits light. An OLED light source is a thin, flexible sheet of material consisting of three layers, a polymer or sublimed molecular film sandwiched between two layers of electrodes, one of them transparent. Current passes through the material until it emits light through its transparent layer.

According to Uniax Corporation, in laboratory conditions, low-voltage OLED light sources can reach efficacies of 3-4 LPW. Unfortunately, such efforts produce too much heat and reduce the life of the light source. Manufacturers including Uniax, Philips Electronics NV, Photonics Spectra, Seiko Epson, Hoechst Innovative Display Technologies Inc., DuPont and Intel are all currently working on developing commercial OLED products.

What is interesting about this light source still in development is that it may challenge our very perception of lighting and architecture in the future. Lighting designers often try to integrate lighting hardware and architecture in a cohesive manner; with OLEDs, the architecture may be the lighting hardware. Sheets of material can be cut and placed like lighting wallpaper or integrated with building materials such as wood, glass and other materials, converting them into luminous surfaces.

The Next Step
Based on current lumen packages and the great potential for this light source to be adopted for more general lighting applications, the next step is for the fixture community to begin building more products designed to utilize LEDs as the primary or supplementary light source. Writes Andrew Bierman of the Lighting Research Center in the LRC white paper, LED: From Indicators to Illuminators?

There are many lighting applications that require only a few lumens, or tens of thousands of lumens, for which LEDs are ideal. In the past, most of the talk about LEDs has focused on efficiency. Now that the efficiencies have exceeded other light sources, future work should focus on packaging LEDs into useful products.
 
Lighting Design Lab
 
 

 

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