LED and lifetime: What do you need to know?

In this blog, we provide you with all the necessary knowledge about LED and lifetime. At the bottom of the blog you can also watch an exciting video on the subject.

Extraordinary longevity

Traditional light sources such as halogen lamps, incandescent bulbs and fluorescent tubes all have the same problem: short lifespan. This is a challenge for anyone who uses these light sources for lighting, as having to replace the bulbs or tubes frequently can cause problems.

This challenge can largely be solved by using LEDs instead of these traditional light sources. LEDs are known to have a superior lifespan, with a general life expectancy of 50,000 hours.

What should you pay attention to in terms of LED lifetime?

It is important to remember that the lifespan of LEDs is partly dependent on things other than the lifetime capacity of the LED itself. Thus, there are several external factors that must be taken into account.

Keep in mind that the LED, i.e. the light source, and the driver, i.e. the transformer, are part of a single system and are therefore interdependent. Therefore, it is necessary to look at which driver is used, as a shorter lifespan of the driver can cause problems for the LED's lifespan.

In addition, the temperature at the location where the LED is installed should also be taken into account. For example, if the product is placed in a sauna, the lifespan will be shorter than if it is installed in a cold room. Normally, the lifetime is based on a room temperature of 25 degrees, which is a normal temperature in an office, for example.

Furthermore, it is important to remember that LEDs, like all other technical devices, gradually lose their performance over time. This means that LEDs do not perform optimally throughout their lifetime, despite the fact that they continue to function.

In this context, it is relevant to get acquainted with different standards that are important to focus on when using LED lighting.

Standard for luminous flux

Luminous flux standards measure how much light is emitted by the light source in a given period of time, and this is what is referred to as LED lifetime.

LED lifetime can be defined as the operational time period during which an LED will maintain a certain percentage of its original luminous flux. Thus, lifetime is measured in the context of selected percentage of the original luminous flux of the LED, and lifetime is described as LP. LP can be called a durability or duration measure of lifetime. Thus, an example would be L70, which means that it is measured when the luminous flux has dropped to 70% of the original luminous flux.

As an example, one of the most common standards for the deterioration or weakening of luminous flux, i.e. light, over time is used:

The L70 standard: Measuring an LED according to this standard tells us how many hours the light source can shine before its luminous flux has dropped to 70% of its original luminous flux.

For example, a light source may be measured at L70 after 50,000 hours, whereby we can deduce that the luminous flux of the light source has dropped to 70% of its original luminous flux after it has been on for 50,000 hours. It is important to note that from the time the LED is installed and for the next 50,000 hours, the luminous flux gradually decreases to 70% of its original level. However, this does not mean that the LED stops glowing after 50,000 hours, just that it only glows at a maximum of 70% of its original power. This percentage will then gradually decrease for the rest of the LED's lifetime.

Below is a graph illustrating the L70 standard for an old metal halide lamp. Luminous light sources span a wide range of types. These include metal halide lamps, fluorescent tubes and LED light sources. What they all have in common is that the brightness fades over time.

Standard for average lifespan

The LED average lifetime standard measures the average lifetime of a specific LED model statistically measured based on test trials performed on a large number of samples of the LED model.

The average lifetime can be defined as the lifetime that can be attributed to a particular LED model based on statistical measurements, thereby deriving a median operational lifetime of the model.

It is the task of the LED model manufacturer to specify this average lifetime and to define a failure rate. The unit of measurement for average lifetime is Bp and is measured in hours, where p stands for percent.

As an example, B10 can be used to illustrate average lifespan:

The B10 standard: If an LED model is measured according to this standard, we will know what percentage of LED models have technical faults that cause it to fail to light for a set number of hours. For example, a model may be measured to have B10 at 30,000 hours, whereby it can be deduced that only 10% of the tested products failed within the first 30,000 hours.

Error rate standards

LP and Bp in combination can show how many of the products' luminous flux for a specific LED model has dropped a certain percentage after a certain number of hours. To set up an example, L70 B20 can be used:

L70 B20: B2o is an expression of the failure rate and shows a 20% failure rate of the products at a certain number of hours, e.g. 50,000 hours. L70 B20 means that the luminous flux of the LED model has decreased by 30% after 50,000 hours and a maximum of 20% of the measured products are defective.

The TM-21 test method

With this test method, consumers can obtain long-term lifetime information for LED light sources. The method is based on two steps:

The LED light source is tested with L80.

The data is compared with already collected measurement data so that valid lifetime projections can be made. These projections also take into account external factors such as temperature.

TM-21 is a demanding and comprehensive measurement method. The method requires the specific LED model to be tested for 6,000 hours, after which the lifetime can be reported under TM21. The complexity and scope of the method means that not many manufacturers offer products that have been tested via this method, but at Lumega we use this method to give our customers the best possible lifetime projection of our products for the benefit of our customers.

Video about LED and lifetime