LRC Responds to AMA on LEDs

You may remember that in June of last year the American Medical Association (AMA) released a report called “Human and Environmental Effects of Light Emitting Diode (LED) Community Lighting.” The report made some noise in the general press because it supported the idea that blue light from blue-pump white LEDs contribute to disability glare and retinal damage.

In the lighting community there was a considerable amount of frustration and anger over the report for several reasons. First, there were quite a few references cited that were either hearsay, such as a New York Times article about Brooklyn residents who didn’t like their new LED street lights, or were irrelevant, such as several articles about the effect of skyglow on nesting turtles. The other reason was that there was not a single lighting designer or researcher on the panel. Overall, it was a poorly researched paper that didn’t deserve the attention it received.

Shortly after it was issued, the Lighting Research Center at RPI issued a response paper. On March 15 the authors of that paper held a webinar to further address the AMA report. A video of that webinar is now available. If you’ve got an hour, take a look.

The key takeaways regarding the hazard of blue light from LEDs and the report are:

  1. The criteria of blue light hazard for retinal damage is much more than just color temperature, and includes the source size, intensity per unit area on the retina, and SPD of the light source.
  2. Disability glare is not a function of light source SPD, as the AMA paper suggests, although discomfort glare is. Short wavelengths increase discomfort glare.
  3. Color temperature is the wrong measurement to determine whether or not a light source will affect the circadian system and melatonin production because color temperature does not provide complete SPD information.       For example, some 3,000 K LEDs can have a greater impact than 4,000 K LEDs.
  4. The criteria of blue light hazard for circadian disruption from a light source include – the intensity, duration of exposure, timing of exposure, and SPD.

Street Lighting and Blue Light Information from the Department of Energy

News stories generated by the American Medical Association’s (AMA) community guidance on street lighting has elevated the topic of LED street lighting and its potential effects on health and the environment in the public’s mind. Discussions of these issues have many misperceptions and mischaracterizations of the technical information, and the difference between what has and hasn’t been scientifically established is often blurred.

DOE has assembled a variety of resources on the topic, to provide accurate, in-depth information that clarifies the current state of scientific understanding.

Source: Street Lighting and Blue Light | Department of Energy

Lighting For Plant Health

I have a current project with a green wall, aka living wall, and other greenery in the space. I’ve been given conflicting information about the lighting requirements I need to meet are and how to measure them, so I did some research. This isn’t definitive, but here’s what I’ve found.

First of all, the measurement units that we’re all familiar with don’t apply to horticulture because the average plant’s response to light is very different from that of the human visual system. We know that the human eye response curve is V(λ) (pronounced vee lambda) which is shown in Figure 1. Our response to electromagnetic energy falls between 380 and 770 nm, with a peak response at 555 nm. In order to measure light the way the human visual system perceived it, V(λ) is folded into the definition of the lumen, the footcandle, etc.

Figure 1 V(λ)

Plants, however, have a response curve called the photosynthesis action spectrum, shown in Figure 2. The wavelengths of light that are absorbed and used by plants are below 520 nm and above 610 nm [i], which roughly equates to the blue and red range of the visible spectrum. Plants need a great deal of red light, a far amount of blue light, and little or no green light.

photosynthetically active spectrum

Figure 2 Average photosynthesis action spectrum of chlorophyll [ii]

So, we can’t talk about the amount of light delivered to plants in a useful way if we’re using lumens and footcandles. The measurement of light for plant health is Photosynthetically Active Radiation (PAR) [iii]. There are PAR calibrated light meters, and digital tools to convert lux/footcandle readings to PAR. Other common measurements are also not relevant to horticulture.

  • Color temperature is a numerical indication of the warmth or coolness of white light, but warmth or coolness are aesthetic criteria and are not relevant in light for plant health.
  • CRI is an indicator of how well a light source allows us to see colors when compared to a reference light source. The response of the human visual system to light is built-in to the CRI calculation. Again, for plant health we are not concerned with seeing the colors of the plants so this metric is not relevant.

 

What kind of light should we provide? Incandescent light has an appropriate balance of red and blue light for plant health, as shown in Figure 3. The power consumption will be high. Fortunately, power consumed by the lighting for plant health is exempt from the energy conservation codes. However, with their short life and high power consumption incandescents are, overall, a poor choice.

Incandescent SPD

Figure 3 SPD for incandescent light of 2800 K, 3000 K, and 3200 K [iv]

High color temperature metal halide lamps have been the horticulture light source of choice for a long time because their SPD provides an appropriate balance of red and blue light (Figure 4). While metal halide lamps are being replaced by LEDs in many applications, I expect they will be available for at least the next decade. For my project, these fixtures would only to be used during the green wall’s growth period in the morning before the space opens to the public. A second set of fixtures with warmer light will be used when the space is open so that I could light the wall in a way that is in balance with the rest of the space during operating hours.

Metal Halide SPD

Figure 4 SPD for a 4200 K metal halide [v]

One of the exciting features of LEDs is that they permit fine-tuning of the emitted spectrum. With LEDs it is possible to create a light source that closely follows the photosynthesis action spectra. This has been shown to “improve factors such as yield, flavor, color, plant growth, and flowering as well as pest and pathogen management and control.”[[vi] The impact has been studied, and results so far have been positive, for leaf lettuce [vii], cucumbers [viii], and tomatoes [ix], among others. At least one study has noted, however, has “concluded that the response of plants to the applied light is individual and depends on the species,” [x]

Therefore, an alternative to metal halide fixtures is multi-colored LED fixtures. Since multi-colored LED fixtures allow users to control the brightness of each color individually one could opt for a fixture with a Red, Blue, White (RBW), a Red, Red, Blue, White (RRBW), or a Red, Blue, Blue, White (RBBW) set of LEDs. This would permit one fixture to provide light for health and accent light. One possible result of a RBW fixture is shown in Figure 5. This is a much better match to the photosynthesis action spectra than incandescent, metal halide, or white LEDs.

Figure 5 Possible RBW LED produced SPD

For the time being, the people responsible for the greenery have asked me to stay with the tried and true metal halide lamps.  In the near future, as metal halide lamps become rarer, and as LEDs become more common in horticulture, I expect we’ll be changing over to LEDs.

 

References

[i] Yingchao Xu, Yongxiao Chang, Guanyu Chen, Hongyi Lin, The Research On LED Supplementary Lighting System For Plants, Optik – International Journal for Light and Electron Optics, Volume 127, Issue 18, September 2016, Pages 7193-7201, ISSN 0030-4026, http://dx.doi.org/10.1016/j.ijleo.2016.05.056.

[ii] The Science of Food Production, http://www.bbc.co.uk/education/guides/z23ggk7/revision/2.

[iii] Torres, Ariana P., Lopez, Roberto G., Measuring Daily Light Integral in a Greenhouse, Department of Horticulture and Landscape Architecture, Purdue University, https://www.extension.purdue.edu/extmedia/ho/ho-238-w.pdf

[iv] Livingston, Jason, Designing Light: The Art, Science, and Practice of Architectural Lighting, Hoboken: John Wiley and Sons, 2014.

[v] TM-30-15 Advanced Calculator, Illuminating Engineering Society, New York: Illuminating Engineering Society, 2015.

[vi] Davis, Philip A. and Burns, Claire, Photobiology In Protected Horticulture, Food and Energy Security 2016: 5(4): 223-238. http://onlinelibrary.wiley.com/doi/10.1002/fes3.97/full

[vii] Filippos Bantis, Theoharis Ouzounis, Kalliopi Radoglou, Artificial LED Lighting Enhances Growth Characteristics And Total Phenolic Content Of Ocimum Basilicum, But Variably Affects Transplant success, Scientia Horticulturae, Volume 198, 26 January 2016, Pages 277-283, ISSN 0304-4238, http://dx.doi.org/10.1016/j.scienta.2015.11.014.

[viii] Brazaityte, A., et.al.,  The Effect Of Light-Emitting Diodes Lighting On Cucumber Transplants And After-Effect On Yield, Zemdirbyste, Volume 96, Issue 3, 2009, Pages 102-118. https://www.scopus.com/record/display.uri?eid=2-s2.0-73949144018&origin=inward&txGid=7294EF1D0E6304BAA77C73981961A69E.wsnAw8kcdt7IPYLO0V48gA%3a2 (Login Required)

[ix] Brazaityte, A., et. al., The Effect Of Light-Emitting Diodes Lighting On The Growth Of Tomato Transplants, Zemdirbyste, Volume 97, Issue 2, 2010, Pages 89-98, https://www.scopus.com/record/display.uri?eid=2-s2.0-78249276864&origin=inward&txGid=7294EF1D0E6304BAA77C73981961A69E.wsnAw8kcdt7IPYLO0V48gA%3a7 (Login Required)

[x] Fra̧szczak, B., et. al., Growth Rate Of Sweet Basil And Lemon Balm Plants Grown Under Fluorescent Lamps And Led Modules, Acta Scientiarum Polonorum, Hortorum Cultus, Volume 13, Issue 2, 2014, Pages 3-13, https://www.scopus.com/record/display.uri?eid=2-s2.0-84898647440&origin=inward&txGid=7294EF1D0E6304BAA77C73981961A69E.wsnAw8kcdt7IPYLO0V48gA%3a12 (Login Required)

How Bright Are Colored LEDs?

Measuring and describing the brightness of colored LEDs is an increasingly important part of a lighting designer’s practice. They are used more often, and in more types of projects, than ever before. Yet, we don’t have an accurate method for understanding exactly how much light is being produced and how bright it will appear. It’s a problem that the lighting industry needs to solve, and soon.

The human eye does not respond to all wavelengths of light equally. We have the greatest response to the yellow-green light of 555 nm. Our response falls off considerably in both directions.  That is, wavelengths of light do not contribute equally to our perception of brightness. The sensitivity curve of the human eye is called V(λ) (pronounced vee lambda) and is shown below.

The definition of a lumen, the measurement of brightness of a light source, is weighted using V(λ) and essentially assumes that the light source emits light across the visible spectrum – in other words, it produces a version of white light.

Light meters are calibrated to measure white light using V(λ) so that their measurement of brightness corresponds with our perception. Individual colored LEDs emit only a fraction of the visible spectrum, as shown below in the graph of V(λ) and the SPD of a red LED, and that’s the problem.

V(λ) and the SPD of a red LED.

Light meters measure the light that the colored LEDs provide, of course, and this information is included on an LED fixture manufacturer’s cut sheets, but it often makes no sense. For example, an RGBW fixture I’ve arbitrarily selected reports the following output in lumens: Red 388, Green 1,039, Blue 85, White 1,498. Since brightness is additive, the output when all LEDs are at full should be 3,010 lumens. However the Full RGBW output is given as 2,805 lumens! That’s 7% lower than what we expect.

The essential problem is that the colored LEDs give the light meter only a fraction of the spectrum it’s designed to measure. The meter provides a result based on its programming and calibration, but the results are often nonsensical or at odds with our perception. This problem doesn’t affect only architectural lighting designers. Film and TV directors of photography and lighting directors also rely on a light meter’s accurate measurement of brightness in their work, and when using colored LED fixtures the light meter is likely to be wrong. In fact, even white light LEDs can be difficult to measure accurately because of the blue spike in their SPD.

For now, the only way to accurately assess the brightness of colored LEDs is to see them in use. Lighting professionals need to let manufacturers and others know that the current situation is not acceptable, and that an accurate method of measuring and reporting the brightness of colored LEDs is a high priority. Talk to fixture and lamp sales reps, fixture and lamp manufacturers, and decision makers at IES, CIE, NIST and other research and standards setting organizations. There’s a solution out there. We need to urge those with the skills and resources to find it to get going!

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.

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.

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.

New LED Performance Measurements

The Illuminating Engineering Society (IES) has published two new documents related to measuring the performance of Light Emitting Diodes (LEDs).  The titles, as well as the aspects that are included and excluded, reveal the complexity of LEDs.

The basic problem is that LEDs typically do not fail the way other lamps do.  Instead of a failure that results in the end of light output, LED output fades over time.  The result is that at some point, although the LED is still producing light, it is no longer producing enough light for the application so we would say that it has reached the end of its useful life.  LEDs have very long lives and relatively short development cycles so it is entirely possible that by the time testing of an LED is complete a newer product has already replaced it.  This is compounded by the sensitivity LEDs have to temperature, voltage, and other factors that can mean lab measurements differ greatly from real world measurements.  This gives rise to the need for clearly defined testing procedures that reproduce conditions found in typical installations so that designers can rely on the information from the manufacturers.

The first document is LM-84-14 IES Approved Method for Measuring Luminous Flux and Color Maintenance of LED Lamps, Light Engines, and Luminaires.  (In the IES naming system LM stands for lumen maintenance, 84 is the document number, and 14 is the year it was issued or updated.)  It describes the procedures to be followed in obtaining luminous flux (light output) and color maintenance measurements under standard operating conditions.  However, it does not provide information on sampling, or extrapolation of the data for longer time frames.

The second document is LM-85-14 IES Approved Method for Electrical and Photometric Measurements of High Power LEDs, which describes the procedures to be followed in performing accurate measurements of light output of white and colored high-power LEDs.  The procedures do not cover LED arrays or modules, AC driven LEDs, among other things.

These two documents join several others that describe the testing and measuring of LEDs. The first is LM-79-08 Approved Method: Photometric Measurements of Solid State Lighting Products, which describes the procedures for testing and reporting of: total flux (light output); color temperature; color rendering index, electrical power characteristics; efficacy (in lumens/watt).  LM-79 requires testing of a complete lighting fixture.  It does not apply to bare LED packages. LM-79 does not measure the distribution, only the total light output.  As a result, it does not provide us with complete photometric performance of the fixture tested.

The next standard is LM-80-08 Approved Method:  Measuring Lumen Maintenance of LED Light Sources, which is intended to measure only the LED package, not a complete fixture.  LM-80 does not define the end of life for an LED package.  It is simply  method for determining the light output degradation.  LM-80 outlines the testing conditions and the measurement methods that are to be used to measure, track and report the lumen maintenance of an LED package over the course of 6,000 hours.  it does not provide a means of estimating life expectancy or light output beyond 6,000 hours.

TM-21-11 Projecting Long Term Lumen Maintenance of LED Light Sources picks up where LM-80 leaves off. (TM stands for Technical Memorandum)  It recommends a method for projecting the lumen maintenance of LEDs using the data obtained from LM-80 testing.  TM-21 is used to derive L70, which is the number of hours, or life, before the LED package is emitting 70% of the initial lumens.  L70 is the number most frequently used by manufacturers as the life, or the useful life, of their LEDs.