DOE Predicts LED Use and Energy Savings

In September the DOE issued, Energy Savings Forecast of Solid-State Lighting in General Illumination Applications (PDF, 116 pages), the latest edition of a biannual report which models the adoption of LEDs in the U.S. general-lighting market, along with associated energy savings, based on the full potential DOE has determined to be technically feasible over time. The new report projects that energy savings from LED lighting will top 5 quadrillion Btus (quads) annually by 2035. Among the key findings:

  • By 2035, LED lamps and luminaires are anticipated to occupy the majority of lighting installations for each of the niches examined, comprising 86% of installed stock across all categories (compared to only 6% in 2015).
  • Annual savings from LED lighting will be 5.1 quads in 2035, nearly equivalent to the total annual energy consumed by 45 million U.S. homes today, and representing a 75% reduction in energy consumption versus a no-LED scenario.
  • Most of the 5.1 quads of projected energy savings by 2035 will be attributable to two commercial lighting applications (linear and low/high-bay), one residential application (A-type), and one that crosses ­both residential and commercial (direc­tional). Connected lighting and other control technologies will be essential in achieving these savings, accounting for almost 2.3 quads of the total.
  • From 2015 to 2035, a total cumulative energy savings of 62 quads – equivalent to nearly $630 billion in avoided energy costs – is possible if the DOE SSL Program goals for LED efficacy and connected lighting are achieved.

Don’t have time for the full report?  Download the report summary.

DOE OLED Webinar Next Week

OLEDs are making inroads into the lighting marketplace but are not nearly as well understood as LEDs.  On July 28th the DOE will present a webinar on the current state and future of this lighting technology.  The DOE describes it as “This webinar will present highlights from a new DOE study that examines the state of available OLED products, and the technology and market hurdles that prevent wider use of OLEDs.”

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.

The Impact of Computer Usage on Academic Performance

For over a decade research has shown that allowing students to use computers to take notes in the classroom has negative effects, including a lower quality of notes and reduced information retention, as described here, here and here.  Even students who don’t use computers are so distracted by the screens of students who are that they are impacted, too, as described here.

Now researchers at MIT have the results of a randomized trial that they conducted with the United States Military Academy (West Point) that reinforces the finding of previous studies.  The study “prohibited computer devices in randomly selected classrooms of an introductory economics course at the United States Military Academy. Average final exam scores among students assigned to classrooms that allowed computers were 18 percent…lower than exam scores of students in classrooms that prohibited computers. Through the use of two separate treatment arms, we uncover evidence that this negative effect occurs in classrooms where laptops and tablets are permitted without restriction and in classrooms where students are only permitted to use tablets that must remain flat on the desk surface.” (emphasis mine)

I still don’t prohibit computers in my classroom, mostly because sometimes the easiest way to answer a question is to go online and show an application or a fixture cut sheet, and my students follow along to bookmark the sites.  However, I do make students aware of the pitfalls of computer use by including the above links in my syllabus.  Most of them seem to respond to the information by limiting their computer use and using a paper and pen.

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.