In recent years, the LED lighting market has experienced significant growth due to several factors, with green legislation and environmental concerns being among the most influential. LEDs are far more energy-efficient than traditional light sources like incandescent bulbs and are more environmentally friendly than fluorescent lamps, as they contain no mercury. Additionally, they allow for adjustable color and brightness. As a result, LEDs have found widespread use in professional, industrial, and consumer applications. However, the design of solid-state lighting products involves complex, multidisciplinary challenges. This article will focus on the issue of heat dissipation and how thermal simulation can assist development teams in creating reliable, compact, and high-performance products (Figure 1).
Figure 1. Thermal simulation of a lamp and finished product (Photo: Future Facilities Limited)
In reality, the lifespan of LED lamps—typically ranging from 25,000 to 50,000 hours—is not always fully realized. The performance of solid-state lighting products can degrade over time, affecting parameters such as light output quality and quantity, lifetime, and color stability. These performance characteristics are closely tied to the internal temperature within the luminaire or replacement lamp. How effectively the design of the luminaire dissipates heat is directly related to the operating temperature.
Design Challenges
Two other key factors have also impacted the long-term reliability of LED lighting: aluminum electrolytic capacitors used for energy storage in LED drive circuits, and the market demand for more compact luminaires. In addition to mechanical components like fans, aluminum electrolytic capacitors often limit the useful life of many electronic circuits. These capacitors are electrochemical devices that gradually reform their alumina dielectric layer during normal operation, eventually drying out and leading to failure, especially at higher temperatures.
In professional applications, such as entertainment lighting, smaller fixtures are preferred for easier transport and use. In retrofit scenarios, from streetlights to household downlights, the size and shape must conform to existing standards. For directional illumination, it is common to integrate an electronic driver circuit, an LED emitter module, and a lens into the luminaire.
Adaptive Drive Circuit
The LED driver circuit needs to convert AC grid voltage into a low DC voltage to power the LEDs efficiently. Even though LEDs are efficient, they still generate heat, as do components in the driver circuit, particularly power transistors. If all heat-generating components are placed in a small space, the temperature can rise rapidly, potentially exceeding the maximum 100°C that the LED junction can withstand.
LED lamps present a challenge for designers to fit all these components within limited space while ensuring that the internal and external temperatures remain within acceptable limits. At this point, thermal simulation becomes essential, especially throughout the design process. Figure 2 shows an example of a chip module with effective heat dissipation under thermal simulation.
Figure 2. Thermal simulations show that these chip modules exhibit good thermal management characteristics. (Photo: Future Facilities Limited)
Benefits of Thermal Simulation
Traditionally, most design and development work relied on "rules of thumb" to estimate the thermal performance of components, PCBs, or entire systems. Since the design process is iterative, these estimates often required multiple revisions. Each change increased project time and cost and raised the risk of missing hotspots. Moreover, the accuracy of this method was relatively poor, often leading to over-designing thermal management solutions, which could increase product size and cost or even require unnecessary fans, reducing the mean time between failures (MTBF) of the final product.
Thermal simulation enables engineers to design smaller, more cost-effective, and longer-lasting products. It speeds up the iterative design process, allowing experimentation with various thermal management strategies and ultimately reducing time-to-market.
Simulate During Development
The earlier thermal simulation is performed in the design process, the lower the risk of major design changes due to potential thermal issues. Throughout the project, electronics, mechanical, and thermal engineers must collaborate to ensure that thermal simulation results are considered during design and that the impact of any design changes on thermal performance is fully understood. Figure 3 illustrates the interaction between team members with different expertise.
Figure 3. For thermal simulation to be valuable, engineers need to work together. (Photo: Future Facilities Limited)
At the beginning, a simple conceptual model—where all electronic components are represented as a concentrated thermal block—can be used to determine if the luminaire can be cooled within the specified limits (Figure 4). Information such as total power consumption, product size, heat sink size, and fan airflow is available at this stage.
Figure 4. (Photo: Future Facilities Limited)
In the next phase, when the initial product design is established, the thermal modeling tool requires detailed information such as:
- Component location on the PCB;
- Estimated power consumption of key components;
- Dimensions and outline of the lighting fixture housing.
After running the simulation, the temperature profile highlights areas where components may exceed their maximum allowable operating temperature.
Input Data Affects Results
The more accurate the input data, the more reliable the simulation results. Preliminary simulation results can guide PCB designers and mechanical engineers in making changes that improve the thermal performance of the luminaire. As the design evolves, this process repeats.
Before producing the prototype, the proposed final design should be simulated again. To ensure accurate simulation results, more detailed information is needed, including:
- Thermal models of the components, obtained from manufacturers;
- 3D CAD model of the luminaire housing, imported in standard industry formats;
- PCB design from EDA software, using industry-standard formats like IDF and IDX;
- Details of copper traces on the PCB layers;
- Material properties used in the luminaire;
- Latest engineering data on internal device power consumption.
Once the prototype is complete, the development team verifies the simulation's accuracy by measuring physical temperatures. When evaluating these data, it's important to consider the measurement equipment's accuracy, which may include thermocouples, on-chip sensors, or infrared sensors depending on the application.
Thermal Simulation Accuracy
Norbert Engelberts, a thermal design specialist at Optimal Thermal Solutions BV, used thermal simulation tools to develop a range of LED lighting projects. One project involved designing an LED lamp for the European market as a replacement for the 60W incandescent E27 A-type lamp. The goal was to achieve the lowest possible heat sink temperature with convection cooling to maximize lamp life. Thermal modeling was used to optimize the heat sink design, and the simulation was found to be within 5% of the measured temperature.
A similar level of accuracy was achieved when designing downlights. The goal was to find the smallest heat sink that could keep the LED junction temperature within 100°C. The difference between measured and simulated temperatures was only 4.6%.
Engelberts also applied thermal models in the development of streetlights. The challenge was to ensure effective thermal management within an IP66 sealed enclosure, whose size and shape were constrained by the dimensions of the conventional bulb it replaced. The weight of the lamp was critical, so the heat sink had to be minimized without compromising product life. From the initial design to the final version, the average temperature at each point in the lamp was reduced by 19%, with some points dropping by 35%. The final product was only 13% heavier than conventional luminaires but offered greater reliability and energy efficiency.
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