Proc. SPIE. 10378, Sixteenth International Conference on Solid State Lighting and LED-based Illumination Systems
KEYWORDS: Optical components, Light emitting diodes, LED lighting, Solid state lighting, Manufacturing, 3D printing, Additive manufacturing, Printing, Light sources and illumination, Solid state electronics
Low energy use and reduced maintenance have made the LED, a solid-state light (SSL) source, the preferred technology for many lighting applications. With the explosion of products in the marketplace and subsequent price erosion, manufacturers are looking for lower cost materials and manufacturing methods. 3-D printing, also known as additive manufacturing, could be a potential solution. Recently, manufacturers in the automotive, aerospace, and medical industries have embraced 3-D printing for manufacturing parts and systems. This could pave the way for the lighting industry to produce lower cost, custom lighting systems that are 3-D printed on-site to achieve on-time and on-demand manufacturing. One unique aspect of LED fixture manufacturing is that it requires thermo-mechanical, electrical, and optical components. The goal of our investigation was to understand if current 3-D printing technologies and materials can be used to manufacture functional thermo-mechanical, electrical, and optical components for SSL fixtures. We printed heat sink components and electrical traces using an FFF-type 3-D printer with different filaments. The results showed that the printed heat sinks achieved higher thermal conductivity values compared to components made with plastic materials. For electrical traces, graphene-infused PLA showed low resistivity but it is much higher than bulk copper resistivity. For optics, SLA-printed optical components showed that print resolution, print orientation, and postprocessing affect light transmission and light scatter properties. Overall, 3-D printing offers an opportunity for mass customization of SSL fixtures and changing architectural lighting practice, but several challenges in terms of process and materials still have to be overcome.
The concept of connected lighting systems using LED lighting for the creation of intelligent buildings is becoming
attractive to building owners and managers. In this application, the two most important parameters include power
demand and the remaining useful life of the LED fixtures. The first enables energy-efficient buildings and the second
helps building managers schedule maintenance services. The failure of an LED lighting system can be parametric (such
as lumen depreciation) or catastrophic (such as complete cessation of light). Catastrophic failures in LED lighting
systems can create serious consequences in safety critical and emergency applications. Therefore, both failure
mechanisms must be considered and the shorter of the two must be used as the failure time. Furthermore, because of
significant variation between the useful lives of similar products, it is difficult to accurately predict the life of LED
systems. Real-time data gathering and analysis of key operating parameters of LED systems can enable the accurate
estimation of the useful life of a lighting system. This paper demonstrates the use of a data-driven method (Euclidean
distance) to monitor the performance of an LED lighting system and predict its time to failure.
Recently, light-emitting diode (LED) lighting systems have become popular due to their increased system performance.
LED lighting system performance is affected by heat; therefore, it is important to know the temperature of a target
surface or bulk medium in the LED system. In-situ temperature measurements of a surface or bulk medium using
intrusive methods cause measurement errors. Typically, thermocouples are used in these applications to measure the
temperatures of the various components in an LED system. This practice leads to significant errors, specifically when
measuring surfaces with high-luminous exitance.
In the experimental study presented in this paper, an infrared camera was used as an alternative to temperature probes in
measuring LED surfaces with high-luminous exitance. Infrared thermography is a promising method because it does not
respond to the visible radiation spectrum in the range of 0.38 to 0.78 micrometers. Usually, infrared thermography
equipment is designed to operate either in the 3 to 5 micrometer or the 7 to 14 micrometer wavelength bands. To
characterize the LED primary lens, the surface emissivity of the LED phosphor surface, the temperature dependence of
the surface emissivity, the temperature of the target surface compared to the surrounding temperature, the field of view
of the target, and the aim angle to the target surface need to be investigated, because these factors could contribute
towards experimental errors. In this study, the effects of the above-stated parameters on the accuracy of the measured
surface temperature were analyzed and reported.
This study investigated the capability of a mathematical model in estimating the phosphor layer heat transfer of an LED system. The focus was on determining the temperature distribution based on light propagation in the phosphor layer. The mathematical model was built upon past work by Kang et al. and solved numerically with heat generation and transfer incorporated into the model. The model light propagation and heat generation was compared with past research and then used to simulate an experimental study in order to evaluate the solution from the present model and compare it with the temperature measurements of the experimental study. The solution to the temperature distribution using the mathematical model had good agreement with the experimentally measured temperature values using an IR thermal imaging camera. Then the model was used to predict the temperature distribution in the phosphor layer under different heat transfer conditions to provide insight that is difficult to observe in experimental studies due to practical limitations.
The objective of this study was to understand how optical and thermal performances are impacted in a remote phosphor LED (light-emitting diode) system when the phosphor plate thickness and phosphor concentration change with a fixed amount of a commonly used YAG:Ce phosphor. In the first part of this two-part study, an optical raytracing analysis was carried out to quantify the optical power and the color properties as a function of remote phosphor plate thickness, and a laboratory experiment was conducted to verify the results obtained from the raytracing analysis and also to examine the phosphor temperature variation due to thickness change.
Radiant power emitted by high power light-emitting diodes (LEDs) have been steadily increasing over the past decade. High radiation, especially short wavelength, can increase the temperature and negatively affect the primary lens performance of high-power LEDs. In this regards, assessment of lens temperature during operation is important. Past studies have shown large errors when thermocouples are used for measuring temperature in high radiant flux environments. Therefore, the objective of this study was to understand the problem in using thermocouples to measure LED lens surface temperature and to find a solution to improving the measurement accuracy. A laboratory study was conducted to better understand the issue. Results showed that most of the error is due to absorption of visible radiant energy by the thermocouple. In this study, the measurements made using an infrared (IR) thermal imaging system were used as the reference temperature because the IR imaging system is unaffected by radiant flux in the visible range. After studying the thermocouple wire metallurgy and its radiation absorption properties, a suitable material was identified to shield the thermocouple from visible radiation. Additionally, a silicone elastomer was used to maintain the thermal interface between the lens surface and the thermocouple junction bead. With these precautions, the lens temperature measurements made using the J-type thermocouple and the IR imaging system matched very well.
Generally in a white light-emitting diode (LED), a phosphor slurry is placed around the semiconductor chip or the phosphor is conformally coated over the chip to covert the narrowband, short-wavelength radiation to a broadband white light. Over the past few years, the remote-phosphor method has provided significant improvement in overall system efficiency by reducing the photons absorbed by the LED chip and reducing the phosphor quenching effects. However, increased light output and smaller light engine requirements are causing high radiant energy density on the remotephosphor plates, thus heating the phosphor layer. The phosphor layer temperature rise increases when the phosphor material conversion efficiency decreases. Phosphor layer heating can negatively affect performance in terms of luminous efficacy, color shift, and life. In such cases, the performance of remote-phosphor LED lighting systems can be improved by suitable thermal management to reduce the temperature of the phosphor layer. To verify this hypothesis and to understand the factors that influence the reduction in temperature, a phosphor layer was embedded in a perforated metal heatsink to remove the heat; the parameters that influence the effectiveness of heat extraction were then studied. These parameters included the heatsink-to-phosphor layer interface area and the thermal conductivity of the heatsink. The temperature of the remote-phosphor surface was measured using IR thermography. The results showed that when the heat conduction area of the heatsink increased, the phosphor layer temperature decreased, but at the same time the overall light output of the remote phosphor light engine used in this study decreased due to light absorption by the metal areas.