LEDs have their basic characteristics. They are current devices with unique functions. They also have unique system of operation when they are in use. A look at their practical thermal performance is very vital if you must understand how they operate. This is exactly the major goal of this write-up. We’re going to be examining the practical thermal performance of LEDs and how it influences their usage in given applications.
The Mechanisms behind Thermal Shifts
A White LED usually consists of different components. It has a die that emits blue light. It also has a phosphor that converts part of the blue light into white light. The LED also has a silicone encapsulant that protects the die and the phosphor. There’s also a package that contains the whole parts of the LED on which the entire device is mounted. These parts actually contribute to the overall thermal performance of the LED. They also contribute to the thermal aging of the LED. Take for instance the die; there are many kinds of materials used in producing it since there are many manufacturers of LEDs. This influences the thermal performance of the LED involved. The die also has a maximum temperature beyond which it fails. There’s also a thermal run-way temperature at which some parts of the die may become hotter than other parts. This may cause the entire die element to fail.
Again, the wavelength of the emitted blue light usually shifts with thermal aging. The shifting may be small but then the phosphors normally absorb light in a very tight band of wavelengths. If there’s a small shift in the emission of wavelength, it can affect the ability of the phosphor to absorb light. This results in the decrease of efficacy with thermal aging. Actually, the phosphors are vital sources of temperature effects in LEDs. They do absorb a certain amount of wavelength which usually varies with the thermal excitation of the molecules. They also degrade with temperature as time goes on. Most phosphors that emit the red color are known for degrading temperature.
Meanwhile, the encapsulant of an LED is supposed to be strong mechanically. It also supposed to be optically clear. However, it usually has problem when it comes to being optically clear. It has a number of nice properties. It’s usually very cheap but it normally turns yellow as it gets older. However, silicone is now used in replacing the encapsulant. The silicone element accounts of the high brightness of LEDs. It’s known to be better than epoxy but it still remains a polymer. The silicone also turns yellow with time and after experiencing heat over time. This also affects the color of the emitted light. It can as well reduce the efficacy of the LED. When the LED color turns yellow, it’s an indication that other colors are being absorbed.
Electrical performance of LEDs with Temperature
Thermal performance change of LEDs with temperature is usually noticeable as their forward voltage drops. This usually emanates from the die but the forward voltage dropping varies from LED to LED since there are different manufacturers. If for instance you run an LED at a constant current, the device will continue to warm up while the forward voltage goes down with time. As this happens, the overall power of the LED will also begin to go down with temperature. This automatically leads to the reduction of the light output. In most cases, the efficacy of the LED will also begin to reduce. Even if the efficacy remains unaffected in some cases, the light will still continue to drop by the day.
Optical performance of LEDs with Temperature
Actually, the thermal effects on electrical performance of LEDs depend on the capacity of die. The optical effects generally concern all the basic components of the LED. Efficacy and brightness are usually the most commonly discussed effects. They normally decrease with increase in temperature. Again, the temperature also affects the light output even as the efficacy of the LED drops. The color of the light may change as the temperature keeps changing. There may also be a shift in the phosphor emission with temperature.
The thermal effects on LEDs can influence the life time of the devices. There’s a possibility of lumen degradation as the LEDs keep getting affected by several external and internal forces. Generally, there’s no way to estimate 70% lifetime of the LEDs. The only way to know the lifetime is to measure it. However, the measuring process can be very complex. Different manufacturers have their specific ways of measuring the LED lifetime.
Meanwhile, the lifetime of LEDs is actually different from that of other bulbs. For instance, an incandescent bulb has a lifetime of 1000 hours. After the bulb must have been used for 1000 hours, the filaments are likely to be broken. There may also be no more light output. A fluorescent tube has a lifetime of 8000 hours after which its filaments are broken while the light output is also gone. However, the case is quite different with LEDs. The lifetime of an LED is actually the time after which it has lost 30% of its initial light output. At such point, the LED light bulbs may not be burned out. They simply become dimmer. However, the overall lifetime of an LED when the device is completely dead and useless reaches up to hundreds of thousands of hours. An LED can stay up to 50,000 hours. In most cases, the lifetime is usually set by a number of catastrophic failures. These may include lightening strikes, bond wire breaking and other interior damages. When this happens the LED may become completely dead and useless.
From the above, you must have gathered vital pieces of information concerning the practical thermal performance of LEDs as it relates to temperature. It’s now very clear that LEDs are unique devices with lots of functions. You can still know more about them as you keep researching about their performance in the electric industry.