Thankfully LED lights last much longer than the old incandescent bulbs. And even after many hours of lighting, an LED lamp does not simply burn out. Instead, an LED ages with time and its luminosity slowly decreases. This effect is known as degradation or decrease in luminous flux. Here you can find out why LEDs get darker over time.
Do LED lamps get darker over time?
We have become used to a long lifespan of 50,000 hours and more with LED luminaires and light sources. The old incandescent and halogen lamps, on the other hand, broke down after just a few thousand hours. At the end of the life expectancy the filament breaks and the lamp remains dark. Such a sudden defect cannot occur with LEDs. Nevertheless, there are also signs of ageing here, which are called as follows:
- Loss of brightness
- Luminous flux decrease
After purchasing an LED lamp usually has the brightness specified by the manufacturer. Over time, the luminosity slowly decreases and the lamp becomes darker. By the way, this effect also occurs with old incandescent and halogen lamps and especially with energy-saving lamps.
The decrease in LED luminosity is not linear. The luminous flux decreases very slowly in the beginning and decreases faster and faster with time. However, this is an extremely slow process over the entire lifespan. The decrease in luminous flux will therefore not be noticed in practice.
Why do LEDs lose their luminosity?
An LED lamp consists of several components. These include a small power supply, an LED driver and the LEDs themselves. The loss of brightness is mainly due to the structure of the light emitting diode. Minimal impurities in the semiconductor crystal of the LED chip cause material changes over time.
This process progresses slowly due to the heating of the LED each time it is switched on and during the lighting time. An increased ambient temperature or a mounting position with insufficient cooling accelerates the process. The technical term for this aging process is degradation.
What means LED degradation?
The term degradation in connection with LED lighting describes the decrease in luminous flux over the course of a lifetime. The luminous flux slowly decreases due to material changes in the LED chip and clouding of the optics. Degradation is therefore an ageing process in which an LED lamp loses its brightness over time and slowly becomes darker.
How is degradation measured?
In order to determine the percentage decrease in luminous flux of an LED illuminant, the luminous flux must be measured both when new and at the end of the specified lifespan. A comparison of both values shows the difference and provides information about the degradation.
The luminous flux of a light source can be measured using an integrating sphere and a photometer. However, the long life of an LED lamp poses a problem for a real measurement. One would have to wait many years until the real aging of the lamp occurs. For this reason, LED lamps are artificially aged so that more reliable results on the decrease in luminous flux can be obtained more quickly.
Is the degradation indicated?
The nominal lifespan must be specified by the LED manufacturers on the packaging. This does not apply to degradation. However, more and more manufacturers are now stating the reduction in luminous flux on the packaging or in the data sheet. There you will find additional information such as L70 or L80.
With a stated lifespan of 30,000 hours, for example, L70 means a 30% reduction in luminous flux. With L80, the luminosity is only reduced by 20%.
What does this decrease mean in practice?
For many consumers, the drop in luminous flux of LED luminaires and light sources is unknown. Most people suspect that an LED lamp will fail abruptly after the specified life expectancy, similar to its predecessors. Of course, a sudden defect cannot be ruled out with LEDs either. The cause is usually a fault in the electronics. This has nothing to do with LED degradation.
Since the aging process takes place extremely slowly over many thousands of hours, one will not notice the decrease in luminous flux in practice. Even a loss of brightness of 30% would not be noticeable. The difference would only be noticeable if an aged and a new identical LED light source were directly compared.
Now you know the decrease in luminous flux of LED lamps known as degradation. LEDs slowly lose their brightness during the time they light up. The usual loss of luminosity of 30% sounds dramatic at first. Even if the lamp actually gets darker over time, you will hardly notice the process in practice. A gradual loss of brightness is always better than a sudden failure.