Background

While there are several parameters that affect the lifetime of LED lights, it is the LED driver that is the main determining factor. LED drivers or power supplies are vital in providing the variable and highly adaptable range of lighting designs now offered. A poorly designed low quality LED driver can deliver fluctuating current, reduce the quality of light output, and result in flickering and stroboscopic effects.

Because tracking reliability is a challenge that engineers and maintenance managers face on a daily basis, it is easy to understand why questions about Mean Time Between Failure (MTBF) are among the most commonly asked by GRE Alpha customers. The purpose of this article is to help clarify that is it applies to the life span of our LED drivers and the decision-making process.

Defining Terms – Failure Metrics

MTBF has its roots in the aviation industry, where airplane failure can result in fatalities. According to an article by Jonathan Trout in Reliable Plant, "MTBF is a prediction of the time between the innate failure of a piece of machinery during normal operating hours." As it applies to LED drivers, MTBF is a statistical approximation of how long a population of drivers will operate before a failure can be expected. It is expressed in hours and does not represent how long a single unit will last. MTBF is therefore an excellent characteristic for determining how many replacement drivers would be needed to support, say 100 installed drivers. It is the inverse of the field failure rate (1/total field failure rate).

While tracking MTBF can help maximize uptime and keep disruptions to a minimum, it is important to understand that a product with a high MTBF will not necessarily last longer than a similar product. Other data needs to be considered, including function, usability, and the environment.

• Although there are a few different ways to calculate MTBF, one of the most common (and required by many government and commercial purchasing contracts) require a MIL-HDBK-217F prediction report.
• For some basic LED driver information, including life expectancy, you might find it helpful to visit the GRE Alpha website for common questions and answers about LED drivers/power supplies.

Another essential performance metric important in tracking is Mean Time To Failure (MTTF). MTTF represents the length of time that an item is expected to last in operation until it fails and can be useful in understanding the odds of a piece of hardware lasting for your desired period of time. 

• The key difference between MTBF and MTTF is that MTBF applies to repairable systems, while MTTF is for non-repairable equipment (think light bulbs, transistors, and fan belts which will function for a period time before failing permanently, and so only one failure in their lifetime).

The Importance of Reliable Data

The LED driver market is characterized by complex and dynamic design issues and volatile pricing. Understanding failure metrics will enable professionals to determine when a critical asset is most likely to fail with greater accuracy which helps in scheduling maintenance, inventory planning, and system design. Unfortunately, some unscrupulous suppliers remove or add all kinds of MTBF parameters to make their products look good. That's why buying by the lowest price can be risky.

To illustrate the solid performance you can expect from GRE Alpha drivers, here is a typical customer service exchange that explains how MTBF and lifetime are incorporated into our data:

Customer Question:
"According to your datasheets, MTBF for your LED drivers is consistently listed at 55,000 hours. Can you explain how that was calculated?"

GRE Alpha Answer:
We calculate our MTBFs based on actual testing and temperature measurements. The MTBF of our GRE Alpha SLD60, SLD120, and XLD200 series are all stated in our specifications as 55,000 hours (Full load @ 25°C Ambient, Based on MIL-217F)

While you can find claims of MTBF that are significantly higher, odds are high those numbers are based on no testing or thermal measurements in their LED Drivers.

Why Life Expectancy is a better indicator:

• Life Expectancy also starts with measuring a temperature within a driver or power supply. But it is then based on de-rating the internal components based on the actual measured temperatures when in use at full load.
• At the request of some of our customers, GRE started publishing Life Expectancy (or Lifetime) on our integrated drivers (those that are embedded in customer fixtures, such as our XLA and GLV series)
• To elaborate, Life Expectancy or Lifetime of a driver indicates the useful life of operating hours expected under specified normal operating conditions. It is the period of time between starting to use the driver and the beginning of the wear-out phase. This is determined by the life expectancy of components used in the assembly of the unit. The weakest component with the shortest life expectancy determines the life of the whole product. For drivers, electrolytic capacitors have the shortest life expectancy.
• The end product LED fixture introduces external heat, which is controlled by the customer's thermal design. This is more prevalent in Fixtures/Luminaires as opposed to linear rope lighting.
  
  You'll find an example of a GRE lifetime spec here, 2nd page, bottom table: grealpha.com/downloads/model/26/documents/GREalpha_XLA65.pdf

GRE Alpha understands the importance of reliability data in helping businesses run more efficiently and profitably, with minimal downtime and damage. We focus on providing exceptional performance, reliability, and usability by incorporating best-in-class power management technologies and usability features to enable seamless and efficient operation and management of LED lighting systems.

For more information about MTBF or other metrics, LED drivers, dimming modules, and accessories, or to speak with a GRE Alpha product expert, please visit the Enquiries page. We will be more than happy to help.