Reliability Of Light Research Articles

Light at night disrupts trophic interactions and population growth of lady beetles and pea aphids.

Natural variation in light has historically correlated with seasonality, providing an honest cue to organisms with seasonal life history cycles. However, with the onset of widespread light at night (LAN), the reliability of light as a cue has decreased in polluted areas, making its timing or intensity potentially clash with temperature trends. These clashing cues may influence biological systems on multiple levels. Yet, a few studies have connected behavioral underpinnings and larger community-level processes, resulting in a knowledge gap bridging individual-, population-, and community-level responses to mismatched cues. We experimentally investigated impacts of cool temperature and LAN on a lady beetle-aphid-fava system to test how light and temperature influenced aphid population growth and their underlying behavioral drivers. We used Coccinella septempunctata and Coleomegilla maculata beetles to understand the interaction of the environment and predation on pea aphid (Acyrthosiphon pisum) population growth. Aphids and their predators reacted differently to variation in light and temperature, influencing the strength of aphid-driven and predator-driven dynamics in the different conditions. We observed evidence of aphid-driven dynamics in the cool, light conditions where aphids excel and exhibited strong anti-predator behavior. In contrast, we found stronger predator-driven dynamics in warm conditions where lady beetle predatory success was higher. Overall, we found that LAN has context-dependent effects on insect communities due to the varied responses each player has to its environment.

Impact of Solar Light and Electricity on the Quality and Timeliness of Maternity Care: A Stepped-Wedge Cluster-Randomized Trial in Uganda.

We evaluated the impact of solar light installation in Ugandan maternity facilities on implementation processes, reliability of light, and quality of intrapartum care. We conducted a stepped-wedge cluster-randomized trial of the We Care Solar Suitcase, a complete solar electric system providing lighting and power for charging phones and small medical devices, in 30 rural Ugandan maternity facilities with unreliable lighting. Facilities were randomly assigned to receive the intervention in the first or second sequence in a 1:1 ratio. We collected data from June 2018 to April 2019. The intervention was installed in September 2018 (first sequence) and in December 2018 (second sequence). The primary effectiveness outcomes were a 20-item and a 36-item index of quality of intrapartum care, a 6-item index of delays in care provision, and the percentage of deliveries with bright light, satisfactory light, and adequate light. We observed 1,118 births across 30 facilities. The intervention was successfully installed in 100% of facilities. After installation, the intervention was used in 83% of nighttime deliveries. Before the intervention, providers on average performed 42% of essential care actions and accumulated 76 minutes of delays during nighttime deliveries. After installation, quality increased by 4 percentage points (95% confidence interval [CI]=1,8) and delays in care decreased by 10 minutes (95% CI=-16,-3), with the largest impacts on infection control, prevention of postpartum hemorrhage, and newborn care practices. One year after the end of the trial, 90% of facilities had LED lights in operation and 60% of facilities had all components in operation. Reliable light is an important driver of timely and adequate health care. Policy makers should invest in renewable energy systems for health facilities; however, even when reliable lighting is present, quality of care may remain low without a broader approach to quality improvements.

Analysis On Thermal Behaviour Of The Sink And Die Area With Different Thermal Interface Material For High Power Light Emitting Diodes

Its self-heating process directly affects the optical performance and reliability of light – emitting diodes (LEDs). It is important to disperse the generated heat from LED to surrounding atmosphere and keep the LED light performances same as declared by the manufacturer. Thermal interface material (TIM) is applied in between sink and source to reduce contact resistance at the junction between substrate and heat sink interface of the LED modules. This paper provides an assessment on ‘thermal interface materials’. Here different TIM materials used and the performance and problems of these commercial interface materials are discussed. From this study, one can calculate the temperature distribution in the sink area for different types of TIM materials under thermal conductivity perspective and be able to find the capability of dissipation of heat at the end surfaces of heat sinks, and design their system as well. In another process, TIMs with different thickness and input drive currents for the COB-based LED are investigated by using COMSOL simulation software. The results show that the junction temperature of the LED luminaire increases and reduce the lifetime when the input drive current and thickness of the TIM layers increase.

Research of reliability of light emitting diodes to mechanical and climatic loads

Research of reliability of light emitting diodes to mechanical and climatic loads

Shedding light on quality of care: a study protocol for a randomized trial evaluating the impact of the Solar Suitcase in rural health facilities on maternal and newborn care quality in Uganda

BackgroundContinued progress in reducing maternal and newborn morbidity and mortality in low-income countries requires a renewed focus on quality of delivery care. Reliable electricity and lighting is a cornerstone of a well-equipped health system, but most primary maternity care facilities in sub-Saharan Africa are either not connected to the electrical grid or suffer frequent blackouts. Lack of reliable electricity and light in maternity facilities may contribute to poor quality of both routine and emergency obstetric and newborn care, by hindering infection control, increasing delays in providing care, and reducing health worker morale. The “Solar Suitcase” is a solar electric system designed specifically for maternity care facilities in low-resource environments. The purpose of this trial is to evaluate the impact of the Solar Suitcase on reliability of light, quality of obstetric and newborn care, and health worker satisfaction.MethodsWe are conducting a study with 30 maternity care facilities in rural Uganda that lack access to a reliable, bright light source. The study is a stepped wedge cluster randomized controlled trial. Study facilities are identified according to predefined eligibility criteria, and randomized by blocking on baseline covariates. The intervention is a “Solar Suitcase”, a complete solar electric system that provides essential lighting and power for charging phones and small medical devices. The primary outcomes are the reliability and quality of light during intrapartum care, the process quality of obstetric and newborn care, and health worker satisfaction. Outcomes will be assessed via direct clinical observation by trained enumerators (estimated n = 1980 birth observations), as well as interviews with health workers and facility managers. Lighting and blackouts will be captured through direct observation and via light sensors installed in facilities.DiscussionA key feature of a high quality health system is appropriate infrastructure, including reliable, bright lighting and electricity. Rigorous evidence on the role of a reliable light source in maternal and newborn care is needed to accelerate the “electrification” of maternity facilities across sub-Saharan Africa. This study will be the first to rigorously assess the extent to which reliable light is an important driver of the quality of care experienced by women and newborns.Trial registrationClinicalTrials.gov: NCT03589625 (July 18, 2018); socialscienceregistry.org: AEARCTR-0003078 (dated June 16, 2018).

Methodology for Solder-Joint Lifetime Prediction of LED-Based PCB Assemblies

A solder-joint crack due to thermal fatigue affects the reliability of light emitting diode assemblies. A new methodology is presented for the solder-joint lifetime estimation under a wide range of working conditions. The proposed method is based on the combination of reliability design of experiments, computer aided structural analysis validated by thermal-cycling experiments, and surface response modeling.

LED Heat Dissipation Analysis Using Composite Based Cylindrical Slug

The optical efficacy and reliability of light emitting diode is extensively influenced by the operating junction temperature of the LED. Therefore, the evaluation of junction temperature is significant. This paper reports a simulation analysis on the heat dissipation of single chip LED package with based material, copper diamond (Cu/Dia) cylindrical heat slug.Ansys version 11 was utilized as the simulation platform. The junction temperature and stress of the LED chip under natural convection condition were evaluated with varied input power of 0.1 W, 0.5 W and 1 W. Results indicated the maximum junction temperature of LED chip was attained at input power of 1 W.

Experimental and Numerical Investigation of a Microjet-Based Cooling System for High Power LEDs

The optical extraction efficiency and reliability of light emitting diodes (LEDs) relies heavily on successful thermal management due to their inherit dependence on the low junction temperature of LED chips. In this paper, a microjet-based cooling system is proposed for the thermal management of high power LEDs. Experimental and numerical investigations on such an active cooling system were conducted. Thermocouples were packaged with LED chips to conduct an online measurement of the temperature and evaluate the cooling performance of the proposed system. The experimental results demonstrate that the microjet-based cooling system has good cooling performance. For a 2 × 2 LED chip array, when the input power is 5.6 W and the environmental temperature is 28°C, the temperature of the 2 × 2 LED chip array reaches 72°C within 2 minutes and continues to increase sharply if no active cooling technique is applied. By using the proposed cooling system to cool the LEDs, however, the maximum LED temperature measured by thermocouples will remain stable at about 36.7°C, when the flow rate of the micropump is 9.7 mL/s. With consideration of the experimental difficulty, a numerical investigation was conducted on flow and temperature distribution in the microjet device. The feasibility of the numerical model was proven by comparison with experimental results. The numerical results showed that at a flow rate of 3.2 mL/s, the heat transfer coefficient of the impinging jets in the proposed system was about 5523 W/m2·K, and the pressure drop in the microjet device was about 1368 Pa.

Noise as a representation for reliability of light emitting diode

Through the research of the internal structure of Light Emitting Diode (LED), we discovered that the interface trap density and diffusion current ratio are key factors determining the performance of LED, and they are also closely related to the reliability of LED. Among the many kinds of internal noises in LED, low-fre quency 1/f noise describes the interfoce trap density and diffuse current ratio effectively. Based on the mechanism of carrier number fluctuation and carrier mo bility fluctuation of 1/f noise, we put forward the electrical model and 1/f noi se model of LED. We also measured the electrical noise of the device over a wide range of current. Experimental results agree well with the proposed model. Usin g the experimental data, the relationship between noise and the performance and reliability of LED is established. It is proved that the larger the noise magnit ude, the nearer the current exponent is to 2, leading to the degradation of devi ce reliability and significant rise in device invalidation rate.

Internal Mechanical Stresses and Conductivity Mechanisms of p-n-InAsPSb/InAs-Heterostructures

ABSTRACTInfluence of internal mechanical stresses (IMS) and dislocations on conductivity mechanisms and reliability of light emitting diode (LED) and laser InAsPSb/InAs double heterostructures has been investigated. It was shown that the presence of lattice mismatch of layers at p-n-heteroboundaries changes LED conductivity mechanisms the same way as longterm working challenges by current. It was determined that LED degradation has barrier character and is followed by appearance and growth of tunnel current components with power dependence of current from voltage. Reliability and external quantum efficiency decrease with growth of lattice mismatch.