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Applications and Demonstration
Lighting Supermarket Freezers with LEDs
The LRC conducted an 18-month field study to compare LED lighting with fluorescent lighting in supermarket freezer cases. The study included a survey of shoppers, an energy analysis, and a sales analysis.
Luminance Requirements for Commercial Signage
To better understand the requirements for LED lighted signage, the LRC investigated the luminance of backlighted, channel-letter signs.
Effects of Blue Light on the Sleep Quality of Older Adults 
Through a pilot field study, the LRC set out to demonstrate that exposure to blue light from LEDs, followed by darkness at bedtime, would create a light/dark pattern that the human circadian system would recognize and react to, allowing the elderly to sleep better at night.
Low-Profile LED Fixtures for Elevators
LEDs are an ideal solution for applications requiring small or low-profile light fixtures, but as a relatively untested technology, few manufacturers have been willing to produce them. The LRC developed and evaluated a low-profile LED light fixture for elevators that takes advantage of the lamp’s smaller size, durability, and potentially longer life.
LEDs: Saving Energy in Retail Windows
The LRC investigated the use of colored LEDs in retail display windows through a field study at a popular clothing store. The new window lighting with LEDs demonstrated an energy savings of up to 50 percent and improved shoppers' opinions over the typical bright-white, high-energy design.
Innovative Lighting Solutions for Senior Care Facilities
A new study from the LRC is showing how innovative lighting designs and advanced technologies, including LEDs, photosensors and occupancy sensors, can help seniors in long-term care facilities maintain independence and be more comfortable.
LEDs for Aircraft Passenger Reading Lights
LEDs have been used in niche aircraft lighting applications, such as "No smoking" and "Fasten seatbelt" signs, for quite some time. Recent technology advances have prompted aircraft manufacturers to consider LEDs for more general cabin lighting applications, such as the passenger reading light. However, the question remains whether white LEDs are ready for use in this application. This study investigated the performance of LED and traditional halogen passenger reading lights for compliance with current standards, performance characteristics, and user acceptance.
Evaluating White LEDs for Outdoor Lighting Application
Researchers are working to create white light sources that are suitable for outdoor applications such as signage and landscape lighting.
Evaluation of LEDs for Outdoor Signage Application
Outdoor signs commonly are constructed of neon and cold-cathode fluorescent lamps, but interest in using LEDs has been growing because of the potential for greater energy and maintenance savings and improved performance over current technologies. Presently, there are no standards for signage in terms of luminance, brightness uniformity, or life. Therefore, in order to determine the suitability of LEDs for this application, this study evaluated the performance of LEDs in outdoor signage and identified criteria for setting acceptance standards.
Refrigerated Display Case Lighting with LEDs
Using high-brightness LEDs in refrigerated display cases as a replacement for fluorescent lamps is the focus of this study. Solid-state lighting offers light with less heat.
Use of Colored Light in Display Lighting
Using solid-state lighting to provide color in retail display windows helps to attract potential customers. By using colored light on the display background, researchers discovered that they could reduce the percentage of light output of a high-energy accent light in the display without sacrificing visual appeal or the ability to see objects clearly.
Visual, Perceptual and Circadian
Effects of Dimming on High-power LEDs
Dimming provides not only aesthetic value, but is also an important feature in energy conservation with lighting. But dimming can change light source color and efficacy. The LRC investigated two dimming methods and how they affect the spectrum and luminous efficacy of red, green, blue, and white high-power LEDs.
Chromaticity Shifts in High-Power White LED Systems Due to Different Dimming Methods
Dimming is an essential functional and aesthetic requirement of many types of spaces. The growing interest in white LEDs for general lighting has led to more flexible means of dimming control for these devices. However, maintaining a fairly constant white color while dimming LED systems is a challenge. The objective of this study was to evaluate the chromaticity shift of high-power white LED systems under different dimming methods.
Developing Color Tolerance Criteria for White LEDs
How much color variation between similar white LEDs is acceptable? In this study, LRC researchers conducted a human factors experiment to develop color tolerance criteria for white LEDs. These criteria define at what points humans observe a just-noticeable color difference between LED light sources. This information was then used to establish a color-binning criteria for white LEDs.
Color and Brightness Discrimination of White LEDs
Little is known about the temporal characteristics of white LEDs on visual perception. Researchers are conducting experiments to gather chromaticity and luminance data of white LEDs over time, and testing subjective discrimination of color and brightness differences.
Optical Elements for Mixing Colored LEDs to Create White Light
This study focuses on evaluating several optical elements through computer software simulation to determine the proper mix of monochromatic LEDs to produce white light.
Characterizing Color Properties of LED-Based Reading Lights
The LRC conducted a human factors experiment to verify that when the CRI value is dramatically different for two RGB-mixed LED light
sources, human subject response for color appearance and preference of
objects lit by these sources will be almost the same.
Performance, Metrics and Test Methods
The Impact of Temperature and Phosphor Concentration on the Refractive Index of LED Encapsulants
This study explored the refractive indices of commercially available encapsulant materials used for LEDs and how those indices change as a function of temperature and the amount of YAG:Ce phosphor mixed within the encapsulant. By conducting such a study, one can select a suitable encapsulant for high-power LEDs in order to maximize light extraction.
Nanocrystal Quantum Dots for Use in White LED Lighting Systems
Semiconductor nanocrystals, known as quantum dots, may provide an alternative to phosphors when creating white light LEDs. Quantum dots behave like phosphors, but they can be tuned to radiate any color simply by changing the physical size of the dot. In this study, LRC researchers characterized the photometric and optical characteristics of cadmium selenide (CdSe) quantum dots as a first step toward identifying methods to incorporate these nanocrystals in white LED systems.
Characterizing the Thermal Resistance Coefficient of LEDs
The accuracy of measuring LED junction temperature—a strong predictor of LED performance and life—depends upon the value of the LED's thermal resistance coefficient. But this value can change under different conditions. The LRC explored changes in the thermal resistance of LEDs as a function of power, ambient temperature, heat sink size, and orientation.
Improving White LED Efficiency Through Scattered Photon Extraction (SPETM)
LRC researchers have developed a new method of extracting more light from white LED packages: Scattered Photon Extraction (SPETM). SPE significantly increases the light output and luminous efficacy of white LEDs, up to 80 lm/W.
High-Efficiency, Nitride-Based Solid-State Lighting
Researchers at the University of California at Santa Barbara and the Lighting Research Center spent three years developing a high luminous efficacy white solid-state light source, through a U.S. Department of Energy project.
Benchmarking High-Flux LEDs: A Life Test
For any fixture and lamp, life is an issue. How long will a lamp continue to shine? At what point is its quality and quantity of light output no longer acceptable? Will the color stay constant? Although high-power LEDs generally perform better than previous types, each type and color of LED can perform differently. The LRC studied how LED characteristics change over time under various operating conditions.
Solar-powered LED Lighting for Buildings
The LRC evaluated the system efficiencies of different types of solar-power systems for lighting buildings and the potential for LEDs to be used in solar-powered general lighting applications.
Non-contact Method for Determining Junction Temperature in White LEDs
This study investigated a non-contact method of determining the junction temperature of phosphor-converted white LEDs as a first step toward determining the useful life of systems using white LEDs.
Performance Characteristics of High-Power LEDs
A laboratory experiment was conducted to investigate the performance characteristics of currently available high-power LEDs under various drive conditions and ambient temperatures. Light output degradation and color shift properties as a function of time were measured for five types of commercial high-power LEDs.
Performance Characteristics of Light Emitting Diodes
LED packages feature performance characteristics that often vary widely. Designing an LED luminaire involves designing a product with proper drive circuits and heat sinks to ensure quality performance. This project examines performance characteristics in solid-state light sources.
Projecting the Useful Life of LED Lighting Systems
Lighting systems employing LEDs have grown quite popular. However, their increasing usage raises questions regarding the long-term performance of LED systems. This study explored system-appropriate methods for measuring junction temperature, a primary cause of LED degradation, which could then be used to quickly determine the degradation rates of these lighting systems.
Color Rendering Index (CRI) for LED Light Sources
LED light sources are presenting challenges to researchers evaluating their color rendering characteristics. Luminous efficacy, color rendering index (CRI), and life are the three most commonly used metrics to evaluate a light source. Yet, studies show that with LED-based sources, CRI is not a good predictor of color preference. Researchers are working to devise a more reliable metric.
Determining Contrast Sensitivity Functions for LEDs
LEDs are quickly becoming the choice for many lighting applications that require monochromatic light. However, one potential problem with LED-based lighting systems is uneven luminance patterns. A uniform luminance distribution is important in some applications, such as backlighted signage. The objective of this study was to develop a family of contrast sensitivity functions for high-brightness LEDs that could be used to evaluate the luminance uniformity of backlighted signage.
= Project sponsored by ASSIST
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