A New Report on LED Color Shift

Like other lighting technologies, the color or chromaticity of light emitted by an LED can shift over time.  To address the challenge of developing accurate lifetime claims, DOE, together with the Next Generation Lighting Industry Alliance, formed an industry working group, the LED Systems Reliability Consortium (LSRC).  A new LSRC report, LED Luminaire Reliability: Impact of Color Shift, focuses on chromaticity. The purpose of the new report is not to define limits for specific applications, but rather to enable a better understanding of how and why color shifts, and how that impacts reliability.  Download it and take a look.

Tony Awards Tonight

Tony Awards 2017

This photo is from this morning’s rehearsal of the Tony Awards at Radio City Music Hall.  The show airs tonight on CBS and is hosted by Kevin Spacey.  Our own Ed McCarthy is the lighting director.  It’s going to be a fun show.  Watch it!

Lenore Doxsee, In Memoriam

I’m sad to share the news that Lenore Doxsee, one of my oldest and dearest friends and a Studio T+L associate, passed away on Friday, May 19. It’s hard to say if Lenore was more of a theatre artist or a theatre teacher because she excelled at both, loved both, and wouldn’t give up either. In her last few weeks, she designed scenery and lighting for a 5-hour play in New York, and gave many additional hours of her time supporting and then critiquing her student’s final projects.

Lenore was a passionate, committed theatre artist who never lost sight of her own vision, even as she collaborated with a disparate group of directors and choreographers. She was the Associate Artistic Director and Resident Lighting Designer for Target Margin Theater. Their most recent production, Mourning Becomes Electra with scenery and lighting design by Lenore, closed the day after her death. A prolific designer, she worked on productions in many New York theaters, ranging from New York City Opera to La Mama, HERE Arts Center, Dance Theater Workshop, and The Kitchen. Regionally Lenore designed productions for Lyric Opera of Chicago, Glimmerglass Opera, Indiana Repertory Theatre, Boston Early Music Festival, Pittsburgh Opera, Spoleto Festival USA, and many others. Her designs for dance included collaborations with choreographers Jennifer Monson, Miguel Gutierrez, and Morgan Thorson.  Lenore received two Bessie Awards for her work with Miguel Gutierrez and an Obie Award for Target Margin’s production of Mamba’s Daughters.

Lenore was Head of Lighting Design Training in the Production & Design Studio in the Department of Drama at NYU. Inspired by one of her mentors, Arden Fingerhut, Lenore was deeply committed to her students and their art. If any one of them was in technical rehearsal, odds were that Lenore was there, too, night after night observing, suggesting, critiquing. She always seemed to understand what her students needed to hear or learn, and guided them through their education and beyond with care and compassion.

At Studio T+L, Lenore collaborated on space planning, dimming and control systems, stage fixture inventories, and more for Elmwood Playhouse, Bristol Memorial Theatre Feasibility Study, and Levoy Theatre, among others.

As a friend, Lenore taught me that no dish can have too much garlic or olive oil, that Indian food is delicious, and that seeing bad theatre is better than seeing no theatre. We laughed through a preview of Dance of the Vampires, had dinner parties on her Brooklyn rooftop, and listened to favorite bands at downtown bars. For at least 15 years we’ve had “family dinner” on Sunday nights at a local bar with her husband, Paul Bartlett, and a rotating cast of friends. Lenore’s intellect, wit, and modesty were loved by everyone who knew her. She will be deeply missed, especially on Sunday nights.

On A Site Survey

Yesterday we surveyed a site in D.C. for a possible new Vapiano restaurant.  The NYC flagship renovation begins soon, and a new location opens in Chicago later this year, all with lighting design by Studio T+L.

Hugh Hardy Passes Away

One of America’s greatest and most prolific theatre architects, Hugh Hardy, passed away on Thursday at the age of 84.  We had the great privilege of being the lighting designers for Hugh and his team on the renovation of the public spaces of the New Victory Theatre on 42nd Street, which will open later this year.  His wit, generosity, and knowledge were always evident and always appreciated.  Here is his obituary in the New York Times.

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 Productionhttp://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.

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!

LED Stage Light Reviews

We recently examined several LED stage lighting units for a high school black box theatre with a 20’ high grid. The school is determined to have an all LED system, but doesn’t have the budget for top-of-the-line equipment. Our goal was to find a set of lower priced units with reasonable performance. It turned out to be harder than we thought. Here are our reviews:

Altman Pegasus LED Fresnel. This 140W white light LED Fresnel is a winner. The optics are very good, the intensity is great, and the dimming (when controlled via DMX) is very smooth all the way out. This unit uses standard 7.5” accessories, so the school’s existing accessories will fit it. This is one of the more expensive unit we examined, but the performance makes this fixture worth it.

Chauvet Ovation E-910FC. This 270W profile has very high color rendering (due to the Red, Green, Blue, Amber, Lime color mixing) and great intensity.   The down side is that Chauvet’s optics are very poor. Whenever a shutter is used to shape the beam the multiple LEDs produce multiple shadows. This problem was evident for most of the second and third tier manufacturers. Although we didn’t test a template, we have to assume the same problem would occur, making this unit useless as a profile.

Elation Arena PAR Zoom. This 190W PAR has a motorized zoom, which simplifies making slight adjustments to the beam angle. The intensity was good, as was the dimming. The optics, however, were not. Each of the 19 LEDs has very good primary optics, but there is no secondary optic to homogenize the beam. This results in beam irregularities and produces multiple, clear shadows that would be unacceptable to an audience as close to the stage as they are in a black box theatre.

elektraLite 1018 PAR. This 216W PAR suffers from the same problem as the Elation PAR. There is no secondary optic, resulting in an unacceptable multiplicity of shadows.

ETC Source 4WRD Profile. This 155W white light LED profile is also a winner. The optics, intensity, and DMX dimming are all very good. This unit is $200-300 more than the other profiles we reviewed, but like the Altman Pegasus, its performance means that it can be used in the close quarters of black box theatres.

Osram Kreios Fresnel. This 80W white light LED unit has nice optics and an impressive zoom. The dim speed fading down to zero and up from zero is a little fast, but we think that can be managed by adjusting the dimming profile. Unfortunately, at only 80W this unit is too dim to be useful from a hanging height of 20’.

Osram Kreios Profile. Like the Osram Fresnel, this 100W white light LED unit also has nice optics and an impressive zoom. However, as with the Fresnel, it is better suited to smaller venues with lower hanging heights.

We plan on looking at other units, but our current thinking is that the school should have a base inventory of white light LED profiles (Source 4WRD) and Fresnels (Pegasus) that is supplemented with a small number of color changing profiles (ETC ColorSource).

LEDs In Stage Lighting

In a project meeting yesterday a team member said that LED stage lights would save the owner money.  While there are many reasons to include LED lights in a theatre’s equipment inventory, cost savings is not one of them.  We’ve written a white paper, LEDs In Stage Lighting, that includes an economic analysis and simple rate of return.  Get a copy here.

DOE Predicts LED Use and Energy Savings

The DOE has just 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.