Measuring and Reporting LED Life

We’re putting the finishing touches on a lighting design and as we look at cut sheets we continue to be disappointed that many fixture manufacturers still don’t seem to understand the proper methods of measuring and reporting LED life. For example, an Edison Price cut sheet says that lamp life is “rated 50,000 hours based on L70/B50 criteria.  LM80 report by the LED manufacturer furnished upon request,” a USAI cut sheet says that life is “Based on IESNA LM80-2008 50,000 hours at 70% lumen maintenance (L70),” and a Lighting Services Inc. cut sheet just says “Tested to LM79 and LM80 Protocols” and then gives a life of 50,000 hours. Unfortunately, these statements don’t mean what the manufacturers suggest they mean. Let’s take a look.

Back in the early days of LEDs of lighting (say around 2005!) it was the wild west in terms of manufacturers reporting product life. The rated life of traditional lamps is the amount of time that passes until one-half of a sample set has burned out. LEDs don’t burn out, they just get dimmer and dimmer over time, so many LED manufacturers estimated the amount of time until an LED’s output had fallen to one-half and called that the LED’s life. This led to reported lifetimes of over 100,000 hours, which sounds great until you realize that at 100,000 hours the space you’re lighting is only half as bright as it was at the first hour. How many of our designs provide twice as much light on day one so that we can lose 50% of the light and still provide an acceptable light level? None! Clearly the industry needed another method of calculating life.

Eventually, the industry settled on a loss of 30% of output as the lifetime of an LED. This is in line with the Lamp Lumen Depreciation (LLD) factor applied to many CFL and HID lamps in illuminance calculations. The lifetime to 70% of initial light output is often abbreviated as L70. Many lighting designers have pointed out that a 30% loss of light is pretty poor performance and some manufacturers have responded by providing L80, and even L90, data (that is, the life until the LED has lost 10% of its initial brightness). All of this was a step in the right direction, but there was no standard method for taking the measurements to determine L70.

In 2008 the Illuminating Engineering Society stepped up to clarify things with LM-80-08 Approved Method: Measuring Lumen Maintenance of LED Light Sources. LM-80 (LM stands for Lumen Maintenance) specifies the test conditions and methods to be used to measure and report the lumen maintenance of an LED package. Data is collected every 1,000 hours for a minimum of 6,000 hours. Even accurately collected LM-80 data isn’t ideal, though. LM-80 is used to evaluate LED packages, not entire fixtures, so the conditions of the test (temperature, electrical characteristics of the driver, etc.) may, or may not, be similar to those in the assembled and installed fixture.

Importantly, LM-80 does not provide a method of extrapolating the 6,000 hours of data to predict future performance. As a result, any cut sheet saying that a 50,000 hour life is calculated according to LM-80 is misstating things unless the manufacturer has actually had the same LED packages under test. 50,000 hours translates to nearly six years, to that’s unlikely. LM-80 was revised in 2015 and is now the ANSI standard ANSI/IES LM-80-15 IES Approved Method: Measuring Luminous Flux and Color Maintenance of LED Packages, Arrays and Modules.

How do manufacturers calculate an LED’s life? They (should) use IES TM-21-11 Projecting Long Term Lumen Maintenance of LED Light Sources. TM-21 (TM stands for Technical Memorandum) describes a method for projecting the lumen maintenance of LEDs using the data collected during LM-80 testing. So, a cut sheet should say something like, “L70 life of 50,000 hours based on LM-80 testing data according to TM-21 protocol.”

The statements I quoted at the beginning leave wiggle room for the manufacturers to provide lifetimes that may, or may not, be calculated according to TM-21. TM-21 is the only standard we have that allows us to compare apples to apples, so omitting a statement about using TM-21 as the basis of lifetime calculation should make you suspicious about the reported life. It’s also important to understand that LM-80 is a testing procedure, and TM-21 is a calculation procedure. They are not tests. There’s no such thing as an LED that “passes” LM-80 or TM-21 (as some reps have tried to tell me). LM-80 and TM-21 produce information about the life of an LED that the designer uses to assess the appropriateness of a fixture.

Specifiers need to tell reps and manufacturers that LED life must be calculated according to TM-21. It’s the only way to be sure that the lifetimes of various fixtures are all calculated the same way so that we can make reasonable comparisons. They should also urge the IES to develop a procedure that tests a complete fixture: housing, power supply, and LEDs. That’s going to be the best estimate of the true life of an LED fixture. Yes it will take time, but we need accurate information that is calculated the same way across all manufacturers.

Why Hire A Designer?

We’ve had several people call this year to ask, “Why should I hire Studio T+L when the local sales rep/distributor has offered to do the work?” In one instance the caller was an interior designer we’ve worked with before who wanted help in explaining the role of a lighting designer to a client. In another, it was the client of an architect who was urging that we be brought on board as a theatre consultant. In all cases the owner was looking to save money, and saw adding another consultant to the design team as a potential waste of money. Nothing could be further from the truth.

Why Hire A Lighting Designer?
For starters, the local sales rep or distributor isn’t going to do the work of a lighting designer. She/he will suggest fixtures from the manufacturers that she/he represents. It will be up to the architect/interior designer/electrical engineer to determine if the suggested fixtures meet the project’s needs. What the rep or distributor won’t do is invest the time in meetings with the owner and design team to fully understand the project. The rep or distributor won’t develop a complete approach to the design that includes illumination levels, distribution, aesthetics, and controls. The rep or distributor won’t implement that design by selecting appropriate fixtures and controls, testing those selections through calculations or mockups, and creating the construction documentation. The rep or distributor won’t be available throughout construction to inspect the progress of the work, answer the contractor’s questions, focus the fixtures, and set levels in the control system.

Now, sales reps play a valuable role in acting as a liaison between the design community and the rep’s manufacturers. Distributors play a valuable role in procuring lighting equipment for the electrical contractor and delivering it to the site on time. To increase their sales, and their profit, they may offer assistance to architects, interior designers, electrical engineers, and owners, usually at no charge. That assistance may be useful, but no one should fool themselves into believing they are getting a fully developed design from someone who will participate in the project from start to finish. That’s what a professional lighting designer does, though, and is one of the reasons to hire one.

Why Hire A Theatre Consultant?
Theater consultants are hired for the same reasons as lighting designers, only more so, as we’ve written here. Designing a performing arts space requires extensive collaboration between the architect, owner, users, and theatre consultant, beginning with the very first meeting. The most obvious part of a theatre consultant’s work is designing and documenting the theatre’s special requirements – the form and layout of the theatre, space adjacencies, stage rigging, dimming and control, seating, etc. This work doesn’t happen in a vacuum. At Studio T+L we often say that design is as much a process as it is the product that is delivered at the end of that process. We listen carefully to the artists’ needs and desires, convey them to the design team in language they can understand, and advocate for those needs and desires throughout the design and construction process. We listen to the design and construction team and explain their needs and concerns to the artists. By assisting and guiding the collaboration we help to assure a successful project for everyone.

As in the lighting world, the local sales rep or distributor can’t and won’t design the project. Can they assist in a one-for-one replacement of old equipment? Absolutely. Can they sell the project a set of equipment (rigging, dimming, etc.)? Yes. But they will not, and cannot, provide impartial, wide ranging expertise from start to finish to develop, design, and build a fully thought out and integrated performing arts building. Those important services are only provided by a theatre consultant.

Edison Price “Light In Action”

A former student of mine who works for Edison Price Lighting is organizing a group of seminars they’re calling “Light In Action.”   It takes place here in NYC at EPL’s showroom and factory, and includes demonstrations of lighting techniques, discussions on the future of LEDs (led by a representative from Xicato) and dimming LEDs (led by a representative from eldoLED), as well as a factory tour.   Sounds fun, right?  There are six dates between now and the end of the year.  Visit EPL’s web site for more information.