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 Latest Research
The most recent projects are below. Find earlier projects in the SSL Completed Research Archives.
Applications Research and Demonstration
Standalone PV-LED Lighting for Aviation
The LRC conducted a study to understand the factors that affect the performance of standalone PV-LED lighting systems, especially how the charge controller affects total system performance.
Requirements for Runway Guard Lights 
The LRC conducted laboratory human factors experiments to determine the appropriate luminous intensity and other operating parameters of LEDs used in runway guard lights in order to provide acceptable visibility and safety.
Development of an Energy-Efficent, Ultra-thin LED Luminaire
The LRC explored a novel "ultra-thin" LED luminaire concept to replace downlight, accent, and wall-wash luminaires using incandescent and halogen technologies.
LED Blue Taxiway Luminaires
The LRC explored new luminaire designs and methods of transferring heat from the LED junction to the optics in order to minimize snow and ice buildup on blue airport taxiway luminaires.
Remote Airfield Lighting Systems
Many remote communities, such as those in Alaska, depend on air transport for business and emergency aid. Night landings at remote airfields are often dangerous. The LRC explored ways to help make night landings at remote airports safer and area communities more accessible.
LED Aviation Signal Brightness
LED signal lights have narrower spectral distributions than
incandescent (filtered and unfiltered) signals, resulting in more saturated
colors. Since color saturation increases the perception of brightness, the
Federal Aviation Administration (FAA) asked the LRC to develop a set of
“brightness correction factors” for white, green, and blue signal lights.
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.
Color and Optics
Redefining White Light Chromaticity Boundaries for Aviation
The LRC conducted a human factors investigation of the boundaries in chromaticity space that people perceive as white and recommended new aviation white boundaries that were independent of the color limitations of incandescent sources.
SPETM Technology for Mixed-Color LEDs
The LRC hypothesized that a new approach using SPETM optics with optical diffusers could improve the spatial color uniformity of mixed-color LED systems without sacrificing much efficiency.
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.
LED Performance, Reliability, and Life Prediction
Accelerated Life-test Method for LED Drivers
The LRC conducted a study to understand what factors influence the failure modes of standalone LED drivers, and to develop an accelerated test method to predict the useful life of an LED driver.
Optimizing Remote-phosphor LEDs with Optical Ray-tracing
LRC researchers developed a method to determine the MFP of a phosphor layer that can be used in optical ray-tracing analysis to obtain accurate results.
Extracting More Light From LEDs
An LED’s efficiency is limited by its inability to extract some of the light generated by the chip’s active layer. One reason for this light loss is the refractive index mismatch between the chip and the surrounding medium. The LRC conducted a two-part study: an optical ray-tracing analysis to understand what factors influence light extraction, and a laboratory study to quantify the refractive indices of commercial encapsulants.
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.
= Project sponsored by ASSIST
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