A practical degradation based method to predict long-term moisture incursion and colour change in high power LEDs

The effect of relative humidity on LEDs and how the moisture incursion is associated to the color shift is studied. This paper proposes a different approach to describe the lumen degradation of LEDs due to the long-term effects of humidity. Using the lumen degradation data of different types of LEDs under varying conditions of relative humidity, a humidity based degradation model (HBDM) is developed. A practical estimation method from the degradation behaviour is proposed to quantitatively gauge the effect of moisture incursion by means of a humidity index. This index demonstrates a high correlation with the color shift indicated by the LED's yellow to blue output intensity ratio. Physical analyses of the LEDs provide a qualitative validation of the model, which provides good accuracy with longer periods of moisture exposure. The results demonstrate that the HBDM is an effective indicator to predict the extent of the long-term impact of humidity and associated relative color shift

LED Roadway Luminaires Evaluation - Final Report

This research explores whether LEDroadway luminaire technologies are a viable future solution to providing roadway lighting. Roadway lighting enhances highway safety and traffic flow during limited lighting conditions. The purpose of this evaluation study is to determine the feasibility of transitioning from standard high pressure sodium (HPS) roadway luminaire to LED roadway luminaire on the MoDOT maintained highway system. This study includes performance evaluations, a feasibility analysis and a potential transition replacement program

Prognostics and health management of light emitting diodes

Prognostics is an engineering process of diagnosing, predicting the remaining useful life and estimating the reliability of systems and products. Prognostics and Health Management (PHM) has emerged in the last decade as one of the most efficient approaches in failure prevention, reliability estimation and remaining useful life predictions of various engineering systems and products. Light Emitting Diodes (LEDs) are optoelectronic micro-devices that are now replacing traditional incandescent and fluorescent lighting, as they have many advantages including higher reliability, greater energy efficiency, long life time and faster switching speed. Even though LEDs have high reliability and long life time, manufacturers and lighting systems designers still need to assess the reliability of LED lighting systems and the failures in the LED. This research provides both experimental and theoretical results that demonstrate the use of prognostics and health monitoring techniques for high power LEDs subjected to harsh operating conditions. Data driven, model driven and fusion prognostics approaches are developed to monitor and identify LED failures, based on the requirement for the light output power. The approaches adopted in this work are validated and can be used to assess the life of an LED lighting system after their deployment based on the power of the light output emitted. The data driven techniques are only based on monitoring selected operational and performance indicators using sensors whereas the model driven technique is based on sensor data as well as on a developed empirical model. Fusion approach is also developed using the data driven and the model driven approaches to the LED. Real-time implementation of developed approaches are also investigated and discussed

Thermal management and humidity based prognostics of high-power LED packages

While Light Emitting Diodes (LEDs) hold much potential as the future of lighting, the high junction temperatures generated during usage result in higher than expected degradation rates and premature failures ahead of the expected lifetime. This problem is especially under-addressed under conditions of high humidity, where there has been limited studies and standards to manage humidity based usage. This research provides an analysis of the factors that contribute to high junction temperatures and suggests prognostic techniques to aid in LED thermal management, specifically under humidity stress. First, this research investigates the effects of current, temperature and humidity on the electrical-optical-thermal (EOT) properties. Temperature rises within an LED because of input stressors which cause heat to build up: the input current, the operating and ambient temperature, and the relative humidity of the environment. Not only is there an accumulation of heat due to these factors that alter the thermal properties, but the electrical and optical characteristics are changed as well. By uncovering specific configurations causing the EOT performance to degrade under stress, better thermal management techniques can be employed. Second, this research proceeds to quantitatively link the EOT performance degradation to the humidity causal factor. The recent proliferation of LED usage in regions with high humidity has not corresponded with sufficient studies and standards governing LED test and usage under the humidity stressor. This has led to indeterminate use and consequentially, a lack of understanding of humidity based failures. A novel humidity based degradation model (HBDM) is successfully developed to gauge the impact of the humidity stressor by means of an index which is shown to be an effective predictor of colour degradation. This prognostication of the colour shift by the HBDM provides both academia and industry not only with an indicator of the physical degradation but also an assessment of the LED yellow-blue colour rendering stability, a critical application criterion. Using the HBDM parameters as indicators of the state of the LED, the degradation study is expanded in the development of a Distance Measure approach to isolate degraded samples exceeding a specified multivariate boundary. The HBDM and Distance Measure approach serve as powerful prognostic techniques in overall LED thermal management

Assessment of LED Technology in Ornamental Post-Top Luminaires (Host Site: Sacramento, CA)

The DOE Municipal Solid-State Street Lighting Consortium has evaluated four different LED replacements for existing ornamental post-top street lights in Sacramento, California. The project team was composed of the City and its consultant, PNNL (representing the Consortium), and the Sacramento Municipal Utility District. Product selection was finalized in March 2011, yielding one complete luminaire replacement and three lamp-ballast retrofit kits. Computer simulations, field measurements, and laboratory testing were performed to compare the performance and cost-effectiveness of the LED products relative to the existing luminaire with 100 W high-pressure sodium lamp. After it was confirmed the LED products were not equivalent to HPS in terms of initial photopic illumination, the following parameters were scaled proportionally to enable equitable (albeit hypothetical) comparisons: light output, input wattage, and pricing. Four replacement scenarios were considered for each LED product, incorporating new IES guidance for mesopic multipliers and lumen maintenance extrapolation, but life cycle analysis indicated cost effectiveness was also unacceptable. Although LED efficacy and pricing continue to improve, this project serves as a timely and objective notice that LED technology may not be quite ready yet for such applications

Revision of the EU Green Public Procurement Criteria for Road Lighting and traffic signals

The EU GPP criteria for road lighting and traffic signals aim to address the key environmental impacts associated with the design, installation and operation of these systems. For road lighting, the criteria are broadly split into three parts: energy consumption, light pollution and durability aspects. From an LCA perspective, the main environmental impact was found to be related to energy consumption during the use phase. This impact can be reduced in a number of ways, by using luminaire and light source combinations with a high luminous efficacy, by dimming during periods of low road use and by selection of the lowest necessary light class for roads to prevent unnecessary over-lighting in the first place. Light pollution is another environmental impact of particular relevance to road lighting and traffic signals which is not well addressed by LCA methodologies. In order to reduce the potential for light pollution, EU GPP criteria are proposed based on upward and horizontal light output ratios. Furthermore, limits on Correlated Colour Temperature and blue light output are proposed in order to address concerns about annoyance and ecological light pollution respectively. The durability of light sources and fittings is not only important to environmental impacts but also to life cycle cost. Consequently, the EU GPP criteria set requirements for minimum warranties, ingress protection, control gear failure rates and reparability - in order to ensure that lighting equipment in winning tenders is of sufficient quality and able to deliver a prolonged service life. The implementation of these criteria should also help procurers understand better about aspects that should be considered in road lighting system design (e.g. maximum lighting level, dimming capability), the actual products they are procuring (requirements on provision of instructions and labelling), to keep accurate information about their infrastructure (requirement on asset labelling) and to monitor lighting system performance (requirements on metering and AECI). Overall, a good understanding of road lighting and traffic signal systems and the use of suitable technical specifications in Invitations to Tender should help ensure that the twin benefits of lower environmental impacts and lower life cycle costs for public authorities can be obtained.JRC.B.5-Circular Economy and Industrial Leadershi

Phytochrome Physiology and Plant Perception of Far-Red Photons

Photons are the primary energy source for most life on Earth, as they drive photosynthesis, a process that turns the CO2 in air into food. One crucial parameters for the optimization of growth is leaf area, which determines the ability of a plant to capture photons for photosynthesis. In order to gain access to photons in shaded environments, plants have evolved unique sensors, called photoreceptors, which respond to changes in the color and intensity of light. Far-red photons (photons at the edge of human vision that appear as dim red light) hold particular promise in regulating plant shape and photon capture. These photons are minimally absorbed by chlorophyll, and are thus enriched in the shade – making them a potent signal of the presence of shade. These photons have been shown to increase leaf area and stem elongation, which increase access to photons, and thus increase plant growth. Additionally, the lower energy of far-red photons make them particularly useful for reducing the massive requirement for electrical power in indoor agriculture. Here, I describes how far-red interacts with blue, green, and red photons to affect plant morphology. I compare traditional and newly developed models/metrics that predict the action of far-red through a photoreceptor called phytochrome. Additionally, I discuss their interactions with total photon intensity

Lighting Design with LEDs: An investigation of the information that lighting designers require and receive from the LED Supply Chain, and an empirical study on the implications of lighting design with the use of LEDs

Lighting Emitted Diodes (LEDs) are currently being used in advanced lighting designs, mainly in the leisure industry, due to the technological advantages that they offer. Nevertheless, there have been key problems related to the adoption of LEDs in contemporary lighting design schemes. These include the photometry and colorimetry of LEDs, the limited available standards against which to compare and evaluate LEDs, the inadequacy of uniform definitions, and also the lack or inconsistency of data in the LED supply chain. In light of the above, the thesis aims at examining the implications of using LEDs in the illumination of the leisure industry, given the latest technological advancements. To achieve this goal, the thesis defines the Supply Chain of the LED industry. It discusses the flow of information between LED manufacturers, LED module manufacturers, luminaire manufacturers, lighting designers and end users. It analyzes the kind of information that each of these groups expects and receives from the other groups of the Supply Chain, for different kinds of LED applications. The thesis also discusses the importance of data availability to meet different lighting parameters in LED applications. Finally, the thesis notes the necessity for standards that ensure quality, reliable and comparable data. And it also provides guidelines on various issues that need to be taken into account when designing with LEDs. The thesis adds value to the lighting community by addressing issues not covered by previous research. In fact, it puts the whole “puzzle” of the LED lighting industry together by analyzing its different “pieces”: the market of lighting products, lighting design, standards availability, and end user requirements in the leisure industry. The originality of this research is related to the fact that it discloses the flow of information within the lighting industry and the way that the available knowledge is handled and distributed. The novelty of the thesis is also related to the fact that it reveals how information and data availability influence the adoption of LED technology and the decision making in regard to LED products for different kinds of applications. Through that, the thesis contributes to the lighting community by setting the importance of ‘quality’ lighting parameters when designing with LEDs, and by developing guidelines on how to handle the very fast changing technology of LEDs