Light decay is a common issue in the LED industry which often causes headaches. What is the relationship between LED light decay and the lifespan of LED chips, and how can we solve the problem of led light decay?
The figure indicates a correlation between LED light decay and junction temperature. The junction temperature refers to the semiconductor PN junction, and a higher temperature causes earlier light decay, resulting in a shorter lifespan. The figure shows that at a junction temperature of 105 degrees, the brightness decreases to 70% in only 10,000 hours, while at 95 degrees, it takes 20,000 hours. By reducing the junction temperature to 75 degrees, the lifespan can be extended to 50,000 hours, and even more to 90,000 hours at 65 degrees. Therefore, In order to increase the longevity of LEDs, it is necessary to reduce the junction temperature.
What is LED decay?
LED decay refers to the gradual decrease in the brightness or luminous flux output of an LED over time. This happens due to several factors such as the quality of the LED chip, operating temperature, current, and system design. The reduction in brightness can affect the performance of the LED and ultimately decrease its lifespan. Regular maintenance and care are crucial to minimizing the impact of LED decay and maintaining the optimal performance of the LED.
What is the effect of LED decay?
The effect of LED decay is reduced light output and shorter lifespan of the LED lights. It can also lead to increased energy consumption as the lights need to be replaced more frequently. This can be a significant issue for businesses and individuals that rely on LED lighting for their daily operations, as it can result in increased costs and decreased productivity. Therefore, it is important to take steps to prevent LED decay and ensure that LED lights continue to shine bright for years to come. Finally found a better way is to see the picture.
The figure indicates a correlation between LED light decay and its junction temperature. The junction temperature refers to the semiconductor PN junction, and a higher temperature causes earlier light decay, resulting in a shorter lifespan. The figure shows that at a junction temperature of 105 degrees, the brightness decreases to 70% in only 10,000 hours, while at 95 degrees, it takes 20,000 hours. By reducing the junction temperature to 75 degrees, the lifespan can be extended to 50,000 hours, and even more to 90,000 hours at 65 degrees. Therefore, In order to increase the longevity of LEDs, it is necessary to reduce the junction temperature.
How can we prolong the life of LED?
So when we buy LED lamps and lanterns (all not specifically LED spotlights), we must see if their thermal design is good. From the figure can be concluded that the key to extending its life is to reduce its junction temperature.
To extend the lifespan of LEDs, one can focus on the following points:
Importance of Thermal Design
Why Good Thermal Design is Crucial for LED Lamps and Lanterns? Inadequate thermal design can lead to high operating temperatures, which accelerate LED decay and reduce lifespan. Therefore, it is important to choose LED lamps and lanterns with good thermal design.
Relationship between Junction Temperature and LED Decay
Junction temperature, which is the temperature of the LED semiconductor PN junction, plays a crucial role in LED decay. The higher the junction temperature, the shorter the LED lifespan.
Reduce Junction Temperature
To extend the lifespan of LED lamps and lanterns, it is crucial to reduce the junction temperature. This can be achieved by having a good heat sink to dissipate the heat generated by the LED.
Importance of Choosing the Right Heat Sink
There are various types of heat sinks available in the market, but not all are effective in dissipating heat from LED lamps and lanterns. Choosing the right heat sink is crucial to ensuring optimal thermal management.
Challenges in Measuring Junction Temperature
Measuring the junction temperature can be challenging, as it requires specialized equipment and knowledge. However, understanding the junction temperature can help in comparing the effectiveness of different heat sinks and predicting LED lifespan.
Regular Maintenance and Care
Apart from good thermal design and heat dissipation, regular maintenance and care can also prolong the lifespan of LED lamps and lanterns. This includes cleaning the LED system and promptly replacing faulty components.
While designing a heat sink is beyond the scope of this discussion, it is important to consider the effectiveness of various heat sinks in dissipating heat. Measuring the junction temperature can also help determine the expected lifespan of the LED with the use of a particular heat sink. Therefore, it is crucial to have a reliable method of measuring the junction temperature for accurate comparison and analysis of heat sink performance.
How to measure the LED junction temperature?
There are several methods for measuring the LED junction temperature, including thermocouples, resistance temperature detectors (RTDs), and infrared cameras. Thermocouples and RTDs are invasive methods that require direct contact with the LED, while infrared cameras are non-invasive and can measure the temperature remotely. However, each method has its own advantages and disadvantages, and the choice of method depends on the specific application and requirements.
Junction temperature looks like a temperature measurement problem, but to measure the junction temperature inside the LED, you can’t take a thermometer or thermocouple and put it into the PN junction to measure its temperature. Of course, its shell temperature can still be measured with a thermocouple, and then according to the given thermal resistance Rjc (junction to shell), you can deduce its junction temperature.
But the heat sink is installed after the problem is complicated again. As the general LED is soldered to the aluminum substrate, the aluminum substrate is mounted in the heat sink, if only the heat sink shell temperature can be measured, in order to deduce the junction temperature, you need to know a large number of thermal resistance values. Including Rjc (junction to the shell), Rcm (between the shell to the aluminum substrate should actually also contain a thin film printed version of the thermal resistance), Rms (aluminum substrate to the heat sink), Rsa (heat sink to the air), as long as one of the data is not accurate, it will affect the accuracy of the test.
The following figure gives a schematic of each thermal resistance from the LED to the heat sink. Many of these thermal resistances are combined, making their accuracy even more limited. This means that the accuracy of the junction temperature has to be inferred from the measured heat sink surface temperature is even worse.
The good thing is that there is an indirect way to measure temperature – measuring voltage. So, which voltage is related to the junction temperature? And what does this relationship look like? First, the LED voltammetric characteristics.
Temperature coefficient of LED voltammetric characteristics
We know that LED is a semiconductor diode, and like all diodes a voltammetric characteristic, the same as all semiconductor diodes, this voltammetric characteristic has a temperature characteristic. This voltammetric characteristic is shifted to the left when the temperature rises. The temperature characteristics of the voltammetric characteristics of LEDs are plotted in the figure.
Assuming that the LED is powered by Io constant current, the voltage is V1 when the junction temperature is T1, and when the junction temperature increases to T2, the whole voltammetric characteristic shifts left, the current Io remains unchanged, and the voltage becomes V2. These two voltage differences are removed by the temperature, and the temperature coefficient can be obtained, expressed in mV/oC. For ordinary silicon diodes, this temperature coefficient is about -2mV/oC. But most LEDs are not made of silicon, so their temperature coefficient also has to be determined separately. Fortunately, most of the data sheets of various LED manufacturers give its temperature coefficient.
How to predict the life span of LED Lighting
Based on the junction temperature extrapolation life seems to be a very simple matter, just look at the curve in Figure 1 to know the life of the junction temperature corresponding to 95 degrees, LED can get 20,000 hours. The biggest problem is that the LED lamp heat sink cooling efficiency over time, cooling efficiency declining. Also due to the strong outdoor UV, LED life is also shorter. Ultraviolet light in the encapsulation of epoxy resin aging process mainly plays a huge role, if the use of silica gel can be improved. UV light in the phosphor aging process will also produce some bad effects but is not very serious. However, this method is used to relatively compare the heat dissipation effect of the two heat sinks is more effective. Obviously, the smaller the left shift of the voltammetric characteristics of the heat sink, the better the heat dissipation. In addition, there is still some accuracy in predicting the life of indoor LED lamps.
In conclusion, understanding LED decay is essential for ensuring the longevity and optimal performance of LED lighting. Implementing the ten tips we have outlined in this article can help you reduce the rate of LED decay and extend the lifespan of your LED lighting fixtures. By following these tips, you can save money, reduce energy consumption, and maintain a comfortable and safe environment for your home or workplace.
Remember to choose high-quality LEDs, install them correctly, and maintain them regularly to ensure that they continue to operate efficiently and effectively. By taking these steps, you can not only save money and reduce energy waste but also contribute to a more sustainable future. We hope this article has provided you with useful insights and practical tips for managing LED decay and optimizing your LED lighting system.