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Keeping Your LED Lights Bright: Understanding and Preventing Light Decay

LiGHT DEgAY

LED lamps and lanterns are a new modern energy-saving light source product because of their relatively low energy consumption of common light sources, long life, more soft light and environmental protection, which most consumers respect. Light decay is a serious problem that LED lamps and lanterns have to face, which seriously affects the service life of LED lamps and lanterns. In this article, KingOrnan engineers will take you to a comprehensive understanding of the various aspects of light decay.

Keeping Your LED Lights Bright: Understanding and Preventing Light Decay

What is light decay

As we all know, the light intensity of LEDs will drop as the chip’s junction temperature rises and the light efficiency decreases, an inherent physical characteristic of semiconductors that changes with temperature. Considered as light decay. Light decay refers to the light source due to a long working temperature exceeding the limit value and the light intensity to restore the initial value of irreversible damage phenomenon called light decay. That is the LED light source in the specified time without loss of luminous flux (initial light intensity) and loss of luminous flux (attenuation and non-recoverable light intensity) of the ratio.

The Chinese state has not yet developed the definition of LED light decay and general standards. Still, some standards can be referred to GB/T24823-2009 requires LED module performance requirements specified luminous flux maintenance rate is at the ignition point 3000h, the luminous flux maintenance rate should be not less than 92% only trial indoor lamps and lanterns of a product, the U.S. Energy Star LM-80 regulations 6000H, luminous flux maintenance rate ≥ 94.1% otherwise considered a failure.

What are the main causes of light failure of LED light sources?

Main causes of light failure of LED light sources?

There are two main factors:

First, the quality of the LED product itself.

  • LED chip material is not good; the brightness decay faster.
  • Defects in the production process, LED chip heat dissipation can not be good from the PIN pin export, resulting in high LED chip temperature so that the chip attenuation increases.

Second, the use of the conditions of the problem.

  • LED for the constant current drive, some LEDs use unstable voltage drive, causing the LED attenuation too fast.
  • The drive current is greater than the rated driving conditions.

How to solve the lamp light decay?

How to solve the lamp light decay?

We need to understand the way of heat dissipation from lamps and lanterns; can minimize the problem of light decay. Before discussing the heat dissipation of LED lamps and lanterns, we must first understand junction temperature. The so-called junction temperature is the semiconductor chip (wafer, die) PN junction working temperature; the higher the junction temperature, the earlier the light failure. If the junction temperature of 105 degrees, brightness is down to 70% of the life of only 10,000 hours; at 95 degrees, there are 20,000 hours, while the junction temperature is reduced to 75 degrees, the life of 50,000 hours, 65 degrees when the life can extend more to 90,000 hours. So the key to extending the life is reducing the junction temperature; there are three optimization aspects:

1. The choice of LED beads potting adhesive

For example, the same Epistar 14mil white section chip as a representative, with standard epoxy resin to do the base glue and white glue and packaging glue package out of the LED white light, a single light in the 30-degree environment, a thousand hours later, the attenuation data for light decay 70%; if the D class low decay glue package, in the same ageing environment, a thousand hours of light decay 45%; if the C class low decay glue package, in Under the same ageing environment, the thousand-hour light failure is 12%; if B class low decay glue package, under the same ageing environment, the thousand-hour light failure is -3%; if A class low decay glue, under the same ageing environment, the thousand-hour light failure is -6%.

2. LED lighting design optimization

According to the data of single LED bead ageing, if only one LED bead is lit to work while it is in the ambient temperature of 30 degrees, then the single LED bead working bracket temperature will not exceed 45 degrees. The life of this LED will be ideal at this time. If there are 100 LED beads working at the same time, and the interval between them is only 11.4mm, then the holder temperature of the LED beads around the stack may not exceed 45 degrees, but those LED beads in the middle of the stack may reach a high temperature of 65 degrees. This time theoretically, light decay will be faster, while light decay will be slower with the LED beads around the lamp stack. We design the lamps and lanterns as far as possible, strengthening the thermal conductivity and heat dissipation function. The lower the temperature, the smaller the LED lamps and lanterns’ light decay.

3. LED lamp beads electrical parameters design optimization

According to the experimental results of LED in the case of lower drive current, the less heat emitted, the smaller the brightness. LED solar lamps and lanterns circuit design, for example, the LED drive current is generally only 5-10mA; for the number of lamps and lanterns used with large products such as up to 500 or more, or more, the drive current is generally only 10-15mA. The available LED application lamps and lanterns drive a current is only 15-18mA; very few people design a current of 20mA or more.

Experimental results also show that in the 14mA drive current and add the cover is not ventilated, the air temperature inside to 71 degrees of the environment, a thousand hours of light decay for zero, and 2000 hours of light decay for 3%, which shows that this low decay LED lamp beads in such an environment have reached its maximum limit. Then a large is damage to it.

Therefore, the design of the working electrical parameters of LED lamp beads should be based on the actual situation; if the lamps and lanterns of thermal conductivity and heat dissipation function are very good, LED lamp beads drive current to increase a little is okay, because the heat generated by the LED lamp beads work instantly can be exported to the outside, no damage to the LED. On the contrary, if the thermal conductivity of the lamps and lanterns is not good, the circuit current should be designed to be smaller so that it puts less heat out.

How to systematically identify the LED lamps and lanterns' heat dissipation light failure?

How to systematically identify the LED lamps and lanterns' heat dissipation light failure?

The general LED junction temperature rises, and the luminous flux will drop. Then, we need to measure the illumination changes in the same location; we can invert the junction temperature changes, and the specific approach is:

  1. Choose a place not disturbed by external light, preferably at night, and turn off other lights.
  2. Cold on the light, immediately measure the illuminance of a location, and write down the reading at this time for the “cold illuminance”.
  3. Keep the lamps and illuminance meter position unchanged; lamps continue to work.
  4. Half an hour later, read the illuminance value here, and write down the reading as “hot illuminance”.
  5. If the two values are about the same (10-15%), then the heat dissipation system of this luminaire is good.
  6. The lamp cooling system is questionable if the two values are very far apart (more than 20%).

In addition, we can not just look at the cost to conclude that the radiator is good or bad; we have to choose the most cost-effective, rather than the best of everything, summarized as follows.

  1. Hand touch radiator is very hot, certainly not good, hand touch radiator is not hot, not necessarily good.
  2. In the case of good design, the same weight, which surfaces area is large, which heat dissipation is good.
  3. The same surface area, which weight is heavy, and which heat dissipation is good (the same material).
  4. Radiator fins are not the more; the better, the denser.

If you want to understand the LED power supply fully, please check: Take you to know the LED power supply

Conclusion:

In summary, understanding and preventing light decay in LED luminaires is critical to improving the life of LED luminaires. While light fade is an unavoidable problem, Light Decay can minimize by optimizing the choice of LED bead potting compound and the design of LED lighting. As the industry’s leading commercial lighting brand, Kingornan is committed to providing high-quality LED lighting products to minimize light fade issues and ensure the longest life of LED luminaires. This allows consumers to enjoy bright and long-lasting lighting and contributes to a sustainable future.

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