Factors causing LED white light decay

There is definitely some discrepancy between the data obtained by testing a single LED white light on an aging board and the data obtained by testing the LED white lights when they are assembled into a lamp and aged.

The size of this difference depends on the electrical parameters of the LED when it is working, the design of the lamp, and the environment in which the lamp is used.

First, choose what kind of LED white light.

This is very important. The quality of LED white light can be said to be a very important factor. For example, if the same Jingyuan 14mil white light segment chip is used as a representative, the LED white light encapsulated with ordinary epoxy resin base glue, white light glue and encapsulation glue, after a single light is lit in a 30-degree environment, the attenuation data is 70% after one thousand hours; if it is encapsulated with Class D low-attenuation glue, under the same aging environment, the light attenuation after one thousand hours is 45%; if it is encapsulated with Class C low-attenuation glue, under the same aging environment, the light attenuation after one thousand hours is 12%; if it is encapsulated with Class B low-attenuation glue, under the same aging environment, the light attenuation after one thousand hours is -3%; if it is encapsulated with Class A low-attenuation glue, under the same aging environment, the light attenuation after one thousand hours is -6%.

Why do different packaging processes lead to such big differences?

The main reason is that LED chips are afraid of heat. It is not a big deal if they are heated to over 100 degrees for a short period of time. However, the most worrying thing is that they are exposed to high temperatures for a long time, which will cause great damage to the LED chips.

Generally speaking, the thermal conductivity of ordinary epoxy resin is very small. Therefore, when the LED chip is lit, the LED chip emits heat, and the thermal conductivity of ordinary epoxy resin is limited. Therefore, when you measure the temperature of the LED bracket from the outside of the LED white light to be 45 degrees, the center temperature of the chip inside the LED white light may exceed 80 degrees. The temperature node of the LED is actually 80 degrees, so when the LED chip works at the temperature of the node, it is very tormented, which accelerates the aging of the LED white light.

When the LED chip is working, the center temperature reaches 100 degrees, and it can immediately conduct heat out through the bracket pins 98%, thereby reducing the damage caused by heat. Therefore, when the temperature of the LED white light bracket is 60 degrees, the center temperature of its chip may only be 61 degrees.

From the above data, we can see that the choice of packaging process for LED white lights directly determines the light decay of LED lamps.

Secondly, the working environment temperature of LED lamp beads.

According to the data of single LED white lamp aging, if only one LED white lamp is lit and the ambient temperature is 30 degrees, then the bracket temperature of the single LED white lamp will not exceed 45 degrees. At this time, the life of this LED will be ideal.

If 100 LED white lights are lit at the same time, and the interval between them is only 11.4mm, then the temperature of the brackets of the LED white lights around the light stack may not exceed 45 degrees, but the LED white lights in the middle of the light stack may reach a high temperature of 65 degrees. At this time, it is a test for the LED lamp beads. Then, in theory, the light decay of the LED white lights in the middle will be faster, while the light decay of the LED white lights around the light stack will be slower.

But if the LED lamp beads are more than 25mm apart, the heat they dissipate will not accumulate so much. At this time, the temperature of each LED white light bracket should be less than 50 degrees, which is more conducive to the normal operation of the LED.

If the LED works in a relatively cold environment, where the average temperature throughout the year may be only around 15 degrees or less, the lifespan of the LED will be longer.

Alternatively, when the LED is working, there is a small fan blowing next to it to help it dissipate heat, which is also very helpful for the life of the LED.

Anyway, everyone should know that LEDs are afraid of heat. The higher the temperature, the shorter the LED life, and the lower the temperature, the longer the LED life. The ideal operating temperature of LED is of course between minus 5 and zero degrees. But this is basically impossible.

Therefore, after we understand the ideal working parameters of LED lamp beads, we try to enhance the heat conduction and heat dissipation functions when designing lamps. Anyway, the lower the temperature, the longer the LED life.

Again, the working electrical parameters of LED lamp beads are designed.

According to the experimental results, the lower the driving current of the LED white light, the less heat it emits, and of course, the lower the brightness. According to the survey, in the design of LED solar lighting circuits, the driving current of the LED is generally only 5-10mA; for products with a large number of lamp beads, such as more than 500 or more, the driving current is generally only 10-15mA, and the driving current of general popular LED lighting applications is only 15-18mA, and very few people design the current to be more than 20mA.

The experimental results also show that under a driving current of 14mA, with a cover to prevent ventilation and an air temperature of 71 degrees inside, the low-fading product has a zero light decay after 1,000 hours and a 3% light decay after 2,000 hours. This means that this low-fading LED white light has reached its maximum limit in such an environment, and any greater limit would be a damage to it.

Because the aging board used for aging has no heat dissipation function, the heat generated by the LED when it is working basically cannot be conducted to the outside. This has been proved in the experiment. The air temperature inside the aging board has reached a high temperature of 101 degrees, and the surface temperature of the cover on the aging board is only 53 degrees, which is a difference of dozens of degrees. This shows that the designed plastic cover basically has no heat conduction and heat dissipation function. However, in general lamp design, the function of heat conduction and heat dissipation is taken into consideration. Therefore, in summary, the design of the working electrical parameters of the LED lamp beads should be based on the actual situation. If the heat conduction and heat dissipation function of the lamp is very good, it does not matter if the driving current of the LED white lamp is increased a little, because the heat generated by the LED lamp beads can be instantly exported to the outside, without damaging the LED, which is the best care for the LED. On the contrary, if the heat conduction and heat dissipation function of the lamp is so-so, it is best to design the circuit to be smaller so that it can release less heat.