(1) Performance degradation of phosphors at higher temperatures While there is limited information on the direct relationship between phosphor excitation efficiency in LEDs and temperature, it is well established that temperature significantly impacts the performance and lifespan of phosphors. Manufacturers have conducted tests showing that at 60°C, the excitation efficiency of phosphors decreases by approximately 2%, but this reduction is reversible once the temperature returns to normal. However, this effect is temporary, and long-term exposure to high temperatures can lead to irreversible performance loss, which accumulates over time. In practice, users often observe that white LEDs become brighter after a certain period of use. This phenomenon is commonly seen in low-power LEDs within 1,000 hours of operation, where the luminous flux may even exceed the initial value. Some products from mid-2008 were close to or had already reached 1,000 hours of operation. For low-power packaged LEDs, this condition can last up to 2,000 hours. The cause of this behavior could be attributed to several factors: A: The interaction between the phosphor and the encapsulant may temporarily reduce performance, only to restore it under initial thermal conditions. B: Alternatively, the combination of phosphor and encapsulant might enhance performance. C: The blue LED chip itself may show improved performance during the early stages of operation. Experiments have shown that the luminous flux of white LEDs initially increases and then stabilizes or declines. This trend has been observed across different manufacturers using the same red LED chips, making it difficult to determine whether the issue stems from the phosphor or the packaging materials and process. In life tests of low-power blue LEDs, a similar phenomenon occurs—luminous flux increases in the early stages. As shown in Figure 2, the luminous flux generally rises within about 200 hours, while for plug-in white LEDs, it takes around 100 hours. This suggests that the phosphor's performance may initially improve before degrading over time. After the initial boost in light output, the situation becomes less favorable. For low-power white LEDs, the luminous flux increase is short-lived, and performance begins to decline afterward. High-power white LEDs typically experience an initial increase in luminous flux within 100 hours, followed by instability until around 6,000 hours. Over time, some products show significant fluctuations, and after 6,000 hours, the luminous flux steadily decreases. Most high-power white LED products reach the end of their useful life (with 50% light decay) within 15,000 to 20,000 hours. (2) Rapid decline of blue LED itself Compared to other types of LEDs, blue LEDs have the shortest lifespan. Low-power plug-in blue LEDs typically last between 7,000 and 10,000 hours under 20mA current. In contrast, low-power red LEDs can operate for 8,000 hours at 50mA without noticeable light degradation. Despite consuming 1.8 times more power than blue LEDs, red LEDs maintain stable performance. Yellow and green LEDs also have much longer lifespans, often exceeding 10,000 hours. Therefore, the inherent limitations of blue LED chips contribute to the shorter lifespan of white LEDs that rely on them. From a material perspective, blue and green LEDs are made with different epitaxial structures on sapphire substrates. Although the thermal conductivity of the substrates is similar, the epitaxial structure determines how well the chip can withstand heat. Improving this structure should be a key focus for future advancements. Until significant improvements in the epitaxial material are achieved, efforts have focused on enhancing thermal management by replacing the substrate with a more thermally conductive material. (3) Poor thermal conductivity of LED package base materials Plug-in type low-power LEDs typically use iron as the chip mounting bracket. Iron has poor thermal conductivity, and the small cross-sectional area of the leads further increases thermal resistance. Even with a piranha bracket, the issue of limited thermal dissipation remains. These material and structural choices result in lower thermal performance in low-power packages. The primary cause of light degradation in white LEDs is heat. Therefore, all materials involved in the thermal path of the LED should be carefully considered. As discussed earlier, the base material is a major factor. Other components, such as the solid adhesive, powder glue, and protective lens (encapsulant), also play a role. It has been found that silver paste used for crystal mounting results in a longer lifespan compared to epoxy resin, although the initial luminous flux is nearly one-third lower. On the other hand, epoxy resin-based powders offer higher initial brightness (about 25% higher) but a shorter lifespan than silica gel. (4) The effect of ultraviolet radiation on LED UV radiation primarily affects the chip material, phosphors, and encapsulants. Among these, the encapsulant is most vulnerable. LEDs are not designed to withstand direct sunlight, and any UV light that enters the LED is usually diffused. As a result, the impact of UV on the chip and phosphor is relatively mild.
Solenoid Pump is a type of fluid transfer device that uses a solenoid to create a magnetic field that moves a plunger or diaphragm to pump fluids.DYX has both DC solenoid pump and AC Solenoid Pump. DC solenoid pump,DC solenoid water pump,cleaning solenoid pump,mini solenoid water pump,mini solenoid pump Shenzhen DYX Technology Co.,Limited , https://www.dyxpump.com
The main difference between DC solenoid pump and AC solenoid pump is the power source they use. DC solenoid pumps run on direct current, while AC solenoid pumps run on alternating current.
DC solenoid pumps are commonly used in applications where a low voltage power source is available, such as in battery-operated equipment or vehicles. They are also known for their efficient operation and ability to provide consistent flow rates.
AC solenoid pumps, on the other hand, are typically used in applications where a higher voltage power source is available, such as in industrial settings. They are known for their ability to handle high flow rates and provide reliable performance over long periods of time.
Overall, the choice between a DC solenoid pump and an AC solenoid pump will depend on the specific application and power source available.