As a new type of green lighting, LED lamps are energy-saving, environmentally friendly and long-lived, and are highly respected by customers. But the problem of LED decay is another problem that LED lamps have to face. Uninterrupted light decay has seriously affected the use of LED lamps.
For now, the light decay of white LEDs on the market may be one of the primary issues when marching into civilian lighting. What causes the light attenuation of LEDs? Generally speaking, there are two main factors for the light attenuation of LEDs:
I. Quality problems of LED products:
1. The adopted LED chip is not in good health, and the brightness decays faster.
2. There are defects in the production process, and the LED chip heat cannot be well derived from the PIN pin, resulting in excessively high LED chip temperature and increased chip attenuation.
II. The conditions of use:
1. The LED is driven by a constant current, and some LEDs are driven by voltage to cause the LED to decay.
2. The drive current is greater than the rated drive conditions.
In fact, there are many reasons for the decay of LED products. The most critical issue is the problem of heat. Although many manufacturers do not pay special attention to the problem of heat dissipation in secondary products, the long-term use of these secondary LED products will pay more attention to heat dissipation than there are. LED products are higher. The thermal resistance of the LED chip itself, the influence of the silver glue, the heat dissipation effect of the substrate, and the colloid and gold wire are also related to the light attenuation.
III. Three factors affecting the quality of LED lamps
1. Choosing what kinds of LED white lights
The quality of LED white light is a very important factor. To give some examples, the same crystal 14mil white light segment chip as the representative, the LED white lamp is packed with the ordinary epoxy resin-made base, white light glue and package glue. A single lighting in a 30 degree environment shows its attenuation data for the luminous maintenance rate of 70% after a thousand hours.
If using the Class D low-decay glue package, in the same aging environment, its luminous attenuation per thousand hour is 45%.
If using the Class C low-decay glue package, in the same aging environment, its luminous attenuation per thousand hour is 12%.
If using the Class B low-decay glue package, in the same aging environment, its luminous attenuation per thousand hour is 3%.
If using the Class A low-decay glue package, in the same aging environment, its luminous attenuation per thousand hour is 6%.
2. Considering the working temperature of LEDs chips
According to the aging data of the single LED white lamp, if only one LED white light works and its ambient temperature is 30 degree, then the temperature of the bracket when the single LED white light works will not more than 45 degrees. At this time, the life of this LED will be very ideal.
If there are 100 LED white lights working at the same time, the interval between them is only 11.4mm, then the temperature of the bracket around the white LED lights may not exceed 45 degrees, but those lamps in the middle of the light pile may reach a high temperature of 65 degrees. At this time, it will be a hard test for the LEDs chips because those LED white lamps gathered in the middle will theoretically have a faster light decay, while the lights around the pile will have a slower light decay.
As we know, LED is afraid of heat. The higher the temperature, the shorter the LED lifespan, while the lower the temperature, the longer the LED lifespan. So the ideal operating temperature of LEDs should be between minus 5 and 0 degrees. But that’s basically impossible in practice.
Therefore, we should strengthen the thermal function in the design of the lamps as the lower the temperature, the longer the LED lifespan.
3. Considering the electrical parameters of LEDs chips
According to the experimental results, the lower the driving current, the smaller the heat emitted and the lower the brightness. Basing on the survey, the LED solar lighting circuit design, the driving current of LED lamps is generally only 5-10mA, and if the number of lams is over 500 or more, its driving current is generally only 10-15mA. However, the driver current of general LED application is only 15-18mA, few people design the current to more than 20mA.
The experimental results also show that under 14mA driver current, and the lid impervious to the wind, the air temperature inside reaches 71 degrees, low-decay products, zero light attenuation in 1000 hours, and 3% in 2000 hours, which means that the use of this low-decay LED white lamp has reached its maximum in such an environment and then a major is a damage to it if over its maximum.
Because the aging plate does not have heat dissipation function, so the heat generated by the LED when it works is basically is not transmitted to the outside, especially the experiments proved this point. The air temperature inside the aging plate has reached a high temperature of 101 degrees, while the surface temperature of the lid on the aging plate is only 53 degrees, which is a difference of several tens of degrees. This shows that the designed plastic lid basically does not have thermal cooling function. However, in the design of general lamps, it should consider the function of heat conduction and heat dissipation.
Therefore, in summary, the design of working electrical parameters of the LED chips should be based on the actual situation. If the heat conduction function of the lamp is very good, it does not matter if the driving current of the LED lamp increased a little, because the heat generated by the LED lamp can be exported to the outside, which does not damage the LED lamp. On the contrary, if the thermal cooling function of the lamp is sloppy, it is best to design the circuit to be smaller and let is release less heat.