Category: Lamps

Measuring and Reporting LED Life

I’m putting the finishing touches on a lighting design and as I look at cut sheets I 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.

Somehow (sorry, I don’t know the history of this) 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.

IALD Responds To DOE Energy Conservation Program

As I posted in March, the Emerging Technologies Program of the DOE’s Building Technologies Office asked for pubic comments on extending the minimum efficacy of incandescent lamps used in general illumination applications, specifically:

  1. Incandescent lamps that currently do not have a suitable replacement lamp meeting or exceeding 45 lumens per watt (lm/W).
  2. Gaps in technology that impede (or would likely impede) the design, development and future sale lamps of greater than or equal to 45 lm/W.

On May 13th the IALD published their response. The broad outline of their comments are that, first, the proposed rule to increase efficacy to a minimum of 45 lm/W is almost irrelevant because “the market is already addressing the issue of energy savings from lighting.” They go on to note that according to a recent Commercial Buildings Energy Consumption Survey, the use of electricity for lighting fell by 46% between 2003 and 2012.   Second, there is little to be gained by requiring an increased efficacy for lamps that do not currently have a minimum due to the relatively low numbers of lamps involved. Third, the available technologies (primarily LEDs) do not adapt well to certain lamp types and exhibit a range of problems with dimming.

I support the IALD’s response. Quite frankly, with the low LPDs that are written into the various energy conservation codes, we’re already designing under very tight power budgets. The DOE’s proposal will have no effect on decreasing power consumption because it lags so far behind Standard 90.1 and the IECC.

MIT Creates Incandescent Lamp As Efficient as LEDs

Researchers at MIT and Purdue University have demonstrated an incandescent lamp with an efficacy of 6.6 percent, and with a potential efficacy as high as 40 percent. The paper was published in the April issue of Nature Nanotechnology. The demonstration compares favorably to current low efficacy fluorescent and LED lamps, while the upper limit is double the current maximum efficacy for fluorescents and LEDs.

The lamp uses a flat filament, rather than the coil of typical incandescent lamps, that is held between two plates of glass with a coating similar to a dichroic reflector, which the researchers call a photonic crystal. The plates permit visible light to pass through them, but reflect the infrared light back to the filament further heating it and producing more light. This idea has been with us for a while now, with most major lamp manufacturers producing some version of an IR halogen lamp. The main difference is that the new dichroic-like coating is much more efficient than the coatings currently in use and works at a much wider range of wavelengths and angles.

This is great news for those of us who haven’t bought into the idea that LEDs will make everyone happy, make all of our children above average, and help the country win the war. Between the low LPDs of the current versions of Standard 90.1 and other energy conservation codes, and the high efficacy of LEDs, most of us are compelled to use LEDs as the primary light source in many of our projects whether we want to or not. LEDs are great, but they’re not the best design choice for every application. As my students and readers of my book know, I regard energy efficiency as an important consideration in any lighting design, but not the primary goal. My first goal is to understand and deliver the desired look and feel of the space I’m lighting while providing appropriate light levels. My second goal is to explore the possible techniques and technologies that I can use to achieve my first goal. My third goal is to use the most energy efficient option from among the best options.

As a designer whose primary concern is the quality of the living/working/shopping environment I’m helping to create, I want to have as many tools at my disposal as possible, not just LEDs. At this point, it seems that lamp and fixture manufacturers are fully embracing the LED with very little attention paid to other light sources, with the possible exception of the OLED. If this experimental lamp becomes commercialized, we’d be able to use inexpensive, tried-and-true dimming technologies that deliver the performance we want without any of the problems associated with fluorescents and LEDs (flickering, flashing, dimming curves that are too flat or too steep, inability to dim smoothly to 0%, high cost, etc.).

This lamp wouldn’t be a solution for all lighting situations of course, in the same way that the LED isn’t a solution for all situations, but it would allow us to have true incandescent light in any application that called for it without running afoul of energy conservation codes.

DOE Seeks Information On High Efficiency General Service Lamps

The Emerging Technologies (ET) Program of the United States Department of Energy Building Technologies Office is seeking information from the public on incandescent lamps in general illumination applications.

The ET Program supports applied research and development for technologies and systems that contribute to reductions in building energy consumption and helps to enable cost-effective, energy-efficient technologies to be developed and introduced into the marketplace. The following are key areas of interest:

1. Incandescent lamps that currently do not have a suitable replacement lamp meeting or exceeding 45 lumens per watt (lm/W).
2. Gaps in technology that impede (or would likely impede) the design, development and future sale of greater than or equal to 45 lm/W replacement lighting products

You can download the Request For Information here.

GE To Stop Manufacturing CFLs By End Of 2016

In another example of LEDs growing dominance in the lighting industry, General Electric has announced that it is “breaking up” with CFL lamps, and that it will stop manufacturing and sales of spiral retrofit lamps in the U.S. by the end of this year.    According GE, CFLs and LEDs each accounted for about 15 percent of lamps sales last year.  The sales of LEDs are increasing and sales of CFLs are decreasing.

Who Needs A Lighting Designer? Museums and Galleries!

A few weeks ago I gave a three-hour seminar on lighting museums and galleries to the graduate students in an art curating program at a university here in New York. Condensing everything I’d like to say into less than three hours was tough. The two big questions were what to include and what to leave out. I started with a quick overview of how to think about light and lighting before moving on to basic vocabulary and some common lighting techniques. Then, since LEDs are clearly the future, even when lighting art, I moved on to an overview of both color temperature and color rendering. I talked about reference materials such as the IES Lighting Handbook, intensity and brightness ratios, and other considerations before we moved into their gallery space to use their track light system for some demonstrations.

After the whole affair a faculty member, who sat in on most of the seminar, said he had hoped I would have spent much more time talking about how to use track lights and less time on unimportant issues like design, color temperature, and color rendering (!). I was respectful, but stunned. Focusing track lights is so complex that it requires extensive demonstrations? Understanding that with LEDs the color qualities of the light vary widely, and can only be properly selected when they are understood is unimportant information? Uhh…NO. Or, as my 20 month old niece says, “no no no no.”

Yes, five or ten years ago the default light source in museums was an incandescent or halogen lamp. The color temperature difference was minor and the color rendering of both was excellent. That’s not true today. Look at the cut sheet for any museum grade track light and you’ll see that you have a choice of several color temperatures and CRI values. If ANYONE needs to understand the qualities of light that must be selected when using LED fixtures, if anyone needs to understand the affect that color temperature and CRI have on how colors are perceived, it’s certainly people involved in displaying and lighting art. To me, that means the curators of exhibits and the lighting designers they hire.

As I’ve discussed earlier, changing the color temperature of the light changes the color appearance of objects, as shown below.

Illuminated with Warm White Fluorescent Lamp
Illuminated with 3000 K light
Illuminated with Cool White Fluorescent Lamp
Illuminated with 4000 K light

The phenomenon of color consistency means that the shift in color appearance isn’t as great as one might expect or as these photos suggest, but the shifts are real. If you’ve ever bought a black garment only to discover later that it was actually dark blue you’ve experienced this shift. A similar thing happens when we compare a high CRI light source and a low CRI light source. If your work involves color perception this is basic and critical information.

Curators can be forgiven for not knowing much about this, but if they know nothing how can they collaborate with their lighting designer to show the art as they intend? Administrators and curators of museums and galleries – educate yourselves, then hire a lighting designer!

Use of LED Lamps To Improve Health

Today’s New York Times has an article on several manufacturers’ new LED products that are intended to improve wakefulness, sleep, focus, and other aspects of daily life and health. The article appears on both the business and technology pages, but not on the health page, and I think that’s appropriate.  Although there are testimonials by the consumers of some of these products, there’s no discussion about any peer reviewed science behind them.  In fact, about two-thirds of the way through the article the author finally gets to the fact that, “Researchers are still determining how spectrum and intensity of light affect the brain.”  So, the article is an uncritical look at new LED products that make health claims.  We shouldn’t rely only on the claims of the manufacturers, though – remember the claims of 100,000 hour lifetimes for LED lamps?

I’m not saying that we know nothing about how light affects us, because we know quite a bit.  The question is, “Do we know enough to properly and safely integrate that information into our design practice?” and there things become uncertain.  So, before accepting the claims of manufacturers, or making the same claims to clients, it’s important for designers to be up to date on the current state of research and to understand the strength of the findings, as well as how (and if) those findings can be folded into a design.

There are a few web sites that I find useful for keeping up to date.  The first is the Health and Vision page of the Lighting Research Center’s web site, which has links to many of their recently published research papers.  The second is the Research page of USAI Lighting’s web site.  This page provides links to a mix of newspaper articles and scholarly publications on a variety of topics connected to LED lighting.  The third is the Research page of the IES web site.  Finally, members if the IES can  download copies of Leucos, and non-members can purchase copies.

LEDs continue to revolutionize the lighting industry.  Most manufacturers have ended  research and development for incandescent and fluorescent products. OLEDs are increasing in efficacy and prices are dropping, while new technologies (such as light emitting plasma and quantum dots) are on the horizon or already here. To preserve their client’s money, the occupant’s health and safety, and their own reputations, designers need to make sure that they don’t get swept up in the possibilities that are marketed to them before the facts are in.

OLEDs Are Ready For Their Closeup

Last week I attended a webinar on the history, future, and application of OLEDs presented by Dietmar Thomas of Philips.  It was an interesting and informative hour that has just been posted online.  Perhaps the most surprising thing is that Philips sees commercial lighting fixtures lamped almost exclusively with LEDs and OLEDs as soon as 2020!  The webinar is worth the time.  Take a look.