LEDs are inherently reliable, but harsh applications can put solid-state lighting at risk. This article will explain how to choose the right protective material to improve the life and performance of the LED. With the booming LED and solid-state lighting industries, product developers are applying technology to harsh environments. Now let's discuss the need to protect LEDs and circuit components in harsh environments such as marine applications. Coatings and other protection technologies can extend the life and performance of solid state lighting systems. With the rapid development of the LED market, the right product choice is the key to ensuring LED performance and longevity. In this article, we will highlight the use of LEDs in a variety of environments and how to take appropriate protection in these environments. The development process must ensure reliability while ensuring good optical performance of the solid state lighting system (Figure 1). Figure 1. Diffusion (UR5635) and transparent (UR5634) polyurethane resins offer significant differences in optical performance in solid state lighting systems. LED applications are becoming more diverse; design requirements, location or product capabilities can prove that the challenges faced by LED designers are constantly changing. Like most electronic devices, LEDs perform well until external influences begin to degrade their performance. These effects can include electrostatic attraction from dust, moisture or corrosive environments, chemical or gas contamination, and many other possibilities. Therefore, careful consideration must be given to the end use environment to ensure that the right product can be selected. Opportunity and application The development of LED lighting is attributed to the superiority of LEDs in terms of adaptability, longevity and efficiency over conventional lighting forms. Therefore, it is easy to understand why LED lighting is widely used in a wide range of applications, including household lights, industrial lighting for factories, marine ambient lighting, and architectural lighting and design. Comparing the environmental conditions in standard architectural lighting applications with the marine environment can help us understand the underlying causes of LED degradation. In architectural lighting applications, the LED itself may be covered due to the design of the lighting unit, or the orientation of the LED is such that it may only be exposed to general changes in ambient temperature and humidity. In a marine environment, LED lights may be splashed or soaked by salt water. In addition, in all cases, most of the life of the lamp is working in a salt spray environment. High salt conditions can cause corrosion of printed circuit boards (PCBs), which can degrade performance faster than normal humidity changes. Typically, both conformal coatings and encapsulating resins provide a high level of protection in these environments. Protection option The conformal coating is the first protection we discussed. The coating is typically a thin lacquer that conforms to the outline of the PCB, providing good protection without significantly increasing the weight or volume of the board. They are typically 25-75 microns thick and can be easily used by spraying or dipping techniques. In order to protect the top of the LED, the coating used must have good transparency and remain clear throughout the life of the product in the desired environment. If used outdoors, the coating may need to have good UV stability. Therefore, the best type of conformal coating is based on an acrylic chemical that provides clarity and color stability as well as excellent moisture and salt spray protection. Figure 2 depicts a salt spray test in which an acrylic coating provides excellent protection. Figure 2. Coatings based on different chemical matrices provide varying degrees of performance when exposed to salt spray testing. Typically, the acrylic conformal coating is a solvent based product in which the solvent used is a liquid carrier on which the resin film is deposited. The solvent used is a volatile organic compound (VOC). Since this solvent only exists on the LED for a few minutes during the application phase, this is not a long-standing problem for most systems. In some cases, LED manufacturers have specific requirements for the use of VOC-containing products and other specific chemicals, which are listed in the LED Handbook. In general, chemical compatibility checks help to determine if a solvent-based conformal coating is suitable for a particular LED. Color temperature problem In addition to considering the effect of the coating on the LED, it is also necessary to understand the effect of the coating on the color temperature. Figure 3 depicts the correlated color temperature (CCT) bands that are common in LED illumination. The change in color temperature over time, also known as color maintenance, has been a problem when considering the type of protective medium. It is understood that no matter what material is placed directly on the LED crystal, it will cause interaction, resulting in color temperature shift. Figure 3. The LED is in some typical color temperature bands. CCT changes typically range from warm temperatures to cooler temperatures and vary between different LED types and color temperament bands. In addition, it will vary depending on the protective material applied. This is another area where acrylic conformal coatings have advantages over other chemical materials and product types. Figure 4 depicts a typical color temperature shift for a warm white LED. In order to highlight possible changes in color temperature, it has included different thicknesses and curing mechanisms to highlight possible variations in color temperature. The red line indicates the color temperature boundary of the particular type of LED used; that is, when the LED is purchased, its color temperature may be anywhere between these lines. Figure 4. The color temperature shift depends on the coating thickness and cure time. The thin and thick coatings referred to in Figure 4 represent the minimum and maximum thickness levels of the conformal coating, i.e., 25 and 75 microns. By applying such a film, the color temperature shift is minimized and can be controlled within the boundaries given by the LED manufacturer. Ideally, conformal coatings can be used in all LED applications because of the ease of application of the conformal coating, the small impact on the volume and weight of the lighting unit, the versatility of use, and the effect on color temperature shift. However, it is well known that a solution is usually not available for all applications. As mentioned earlier, conformal coatings provide excellent levels of protection in wet and salt spray environments, but conformal coatings do not provide the highest level of protection in environments where water is often immersed in water, chemical splashes, and corrosive gases. In this case, we recommend considering the sealing resin to provide a higher level of protection. Sealing resin Sealing resins also come in many different chemical types, including epoxy, polyurethane and silicone. In general, epoxy resins provide stronger protection in terms of mechanical impact, but they are not as flexible as other chemicals, which can cause problems during thermal cycling. In addition, standard epoxy systems do not provide clarity and color stability for other systems. Silicone does have excellent transparency and performs well at extreme temperatures, while polyurethane resins provide good flexibility, transparency and high levels of protection in harsh environments. Figure 5 shows the difference in transparency of the three resin chemistries by examining the color difference of the resin after exposure to UV for 1000 hours, thereby highlighting the stability of each resin under outdoor conditions. In this figure, silicone and polyurethane resins are clearly superior to standard epoxy systems. Figure 5. Resin chemistry has different effects on color temperature after exposure to UV for 1000 hours. Environmental exposure Comparing the performance of various products in harsh environments, it also allows users to select products based on end-use conditions. For example, Figure 6 illustrates the effect of a corrosive gas environment on acrylic conformal coatings, polyurethane resins, and silicones. By exposing the three to a mixed gas environment, the percentage of luminous flux of the LED is checked. These results clearly illustrate the importance of choosing the right product for the environment. Although the conformal coating does not deteriorate in the corrosive atmosphere, the surface insulation resistance does not deteriorate, but for the LED, it does not adequately protect the LED because it allows the gas to pass through the thin coating and penetrate the LED, thereby over time. Performance is reduced. Figure 6. Different coating types can cause degradation of optical efficiency when exposed to corrosive gases. The silicone resin also had a similar effect; however, in this case, although the protective layer was rather thick (2 mm vs. 50 microns), the gas was able to pass through the resin and affect the LED. When you compare the results of silicone and polyurethane materials, it is clear that the performance of the two chemical types is different because silicone resins are permeable to gases, while polyurethane resins of the same thickness do not. In this case, optically clear polyurethane resins, such as Electrolube UR5634, are the most suitable protective material for preventing corrosive gases from affecting the LED. Polyurethane resins are considered to be suitable resins for protecting LEDs in many different environments. In addition, they can be retrofitted to provide additional advantages, such as a coloring system, to cover the PCB but not exceed the height of the LED. This resin is used for PCB protection, not only to make the surface pleasing, but also to improve the performance of the lighting fixture by reflecting light out of the PCB and increasing the light output. There is also a special resin used to diffuse the light from the LED. Resins such as Electrolube UR5635 offer two solutions: protection from the surrounding environment and the diffusion of light, so it may not be necessary to purchase a heat shield and cap. Protective material formula It is clear that the sealing resin provides a high level of protection in a range of environments and can be adapted to the application by selecting a chemical type or by formulating a specific resin. However, in the previous section, we discussed that the film conformal coating has little effect on color temperature. When comparing the thickness of the conformal coating with the sealing resin, it is clear that the increased level of protection of the resin is due in part to the fact that it can achieve more coating. The resin can be increased by a depth of 1-2 mm or more, but this depth will also have an effect on the observed color temperature level. Figure 7 shows a typical color temperature shift for LEDs with different thicknesses of polyurethane resin. Clearly, thickness is directly related to the degree of color temperature shift, so this is another important consideration when choosing the right protective material. We know that color temperature shifts will occur, but the repeatability of the LED offset is taken into account. If the offset persists, you can rethink the original LED color temperature. Figure 7. The color temperature varies to varying degrees depending on the thickness of the coating. This article discusses various considerations needed to select LED system protection. Evaluating the environment is critical to the successful selection of the product, both in terms of end-use performance and applicability of the manufacturing process. Conformal coatings are not only easy to use, they fit into the design, but also have excellent levels of protection in wet and salt spray environments. Due to their low thickness, they also have little effect on color temperature. When the conditions become more challenging, it is recommended to switch to a sealing resin. In this case, the choice between chemical types will be determined by the end use conditions and the specific environmental impact. In addition, the thickness of the resin to be added should be considered to ensure adequate protection while minimizing the effects on color temperature changes. (Compile: LEDinside James) If you need to reprint, you need to authorize E-Mail on this website. And indicate "from LEDinside", unauthorized reprint, broken chapters and other acts, this website will be held legally responsible! E-Mail: For more information, please follow LEDinside's official website () or search for WeChat public account (LEDinside). Switcher,Video Switcher,Camera Switcher,Live Stream Switcher Dongguan Tuojun Electronic Technology Co., Ltd , https://www.fibercablessupplier.com