TM-30 Rf: So Big, So Strong, So Smart!

As we know, CRI Ra and TM-30 Rf are both measurements of color fidelity. That is, they compare a test light source to a known reference light source and measure how well the test source matches the reference source. One of the many shortcomings of CRI Ra is that it provides us with a single value. That single value is easy to use, but doesn’t tell us anything about what colors will have increased saturation, decreased saturation, hue change, or will be unaffected.

TM-30 is a tougher test than CRI, so how do Rf and Ra values relate? Lamps with Ra values below about 70 tend to have higher Rf values, while lamps with higher Ra values tend to have reduced Rf values. Of course, this doesn’t mean that the lamps we think of as better have suddenly become worse, it’s just that we’re scoring on a different scale. This means that we can’t draw direct comparisons. For example, Energy Star requires that lamps have a minimum CRI Ra of 80, but that doesn’t mean that they should also have a minimum Rf of 80. Different tests give different results and we have to be careful not to apply the meaning of one to the scores of the other.

IES TM-30’s Rf mathematically compares the appearance, under a test light source, of 99 color evaluation samples (CES) that are derived from real world objects, to the CES appearance under a reference light source of the same CCT. The distance of the color shift for each CES is measured in the CAM02-UCS color space and averaged. Throw in a lot of calculus (which we don’t need to get into) and voila, the Rf value. It’s important to remember that what we get is just a number. TM-30 doesn’t qualify any of the results as good or bad, desirable or undesirable. It presents information to the lighting specifier and allows the specifier to apply education, professional experience, and knowledge about the project to determine whether or not a given light source is appropriate.

As with Ra, the single value of Rf conveys limited information. It is more accurate, but still only tells us the average match or mismatch between the two light sources. What makes TM-30 so powerful and useful is that it tells us much more if we want to know. For example, using the Calculation Tool that can be downloaded with the purchase of TM-30 (which I wish the IES would make freely available), we can see that one common F32T8/830 has the following characteristics:

Rf 78
Rg 102
CCT 2943
Duv 0.0014
Ra 85

This lamp has moderately good fidelity (Rf), a slight increase in saturation (Rg), has a CCT of just under 3000K, and is slightly above the black body locus and therefore is slightly green (Duv). The Advanced Calculation Tool tells us that the R9 value is 2 and that the Rf for skin is 85. It also tells us the (x, y), (u, v), and (u’, v’) chromaticity coordinates (which, frankly don’t mean anything to me, but the information is there). This information is immediately useful and isn’t provided as part of the CRI calculation. In addition, most light source manufacturers don’t tell us the Duv, although understanding it is becoming increasingly important, especially now that NEMA has extended the chromaticity bins for LEDs in ANSI/NEMA C78.377 American National Standard for Electric Lamps – Specifications for the Chromaticity of Solid-State Lighting Products. That’s a post for another time.

As I’ve already discussed, IES TM-30’s color fidelity metric Rf provides us with as little, or as much, information as we want. If you just want top line information that the beige office you’re lighting will continue to look beige, you can have it. An Rf of 78 is probably just fine. If you want to see the fidelity of each of the 16 hue bins because you’re interested in the fidelity of a particular color range, it’s there. If you want to know the Rf value of all 99 color samples you can have that, too! What else? Well, would you like to see the chromaticity coordinates in (x, y) color space, the SPD vs the reference source, or a pictorial comparison of each of the 99 CES? No problem.

Pretty pictures but are they useful? Not as useful as the data given above, but lighting designers do like to see this information, even if it’s difficult to interpret. The CIE 1931 (x, y) color space isn’t perceptually uniform, so the distance we see between the reference source and the test source isn’t very informative. Seeing the SPD is interesting, but no one can read an SPD and know what the light looks like or how it renders colors. The CES Chromaticity Comparison is also interesting, but the red and black dots aren’t connected to one another. With some light sources it’s easy to tell how they relate so we can see chroma and hue shifts, but as Rf drops and color shift increases it gets harder and harder. What is useful are the next two graphics: the Rf value by Hue Angle Bin and by CES.

Now we can see how individual color ranges are affected by the lamp in question. This may be especially useful on certain projects were specific color ranges are present and need to be accurately rendered. The individual CES scores useful for the same reason. However, in my opinion if you want information at that level of detail you’re probably better off doing a mockup and looking at project specific color and material samples instead of the CES.

TM-30 arms the lighting specifier with as much or as little information as needed on a particular project. It also provides additional information that may be important (such as Duv). It then allows the specifier to apply experience and knowledge about the client and the project to determine whether or not a given light source is appropriate. Who could say no to that?

The Advantages of TM-30

In this series of posts about IES TM-30-15 I’ve discussed the problems with CRI and the resistance to adopting TM-30. In this post I’ll discuss the advantages of TM-30 over CRI, and what TM-30 is and isn’t.

Color Samples

Like CRI, TM-30 compares color samples rendered by a given test light source and a reference illuminant of the same correlated color temperature (CCT). The first advantage of TM-30 is the selection of color samples. CRI uses the eight samples show in Fig. 1, which are selected from the Munsell color system.

Figure 1 Colors used to calculate CRI Ra

All eight are of medium value and are not evenly distributed across the color space or across the visible spectrum. This allows lamp manufacturers to “optimize” lamp spectra to score a higher CRI Ra than visual evaluation of the light would indicate. TM-30 uses the set of 99 color samples shown in Fig. 2. These color samples range from pale tints to saturated colors, and are drawn from real world objects including textiles, plastics, skin tones, printed materials, natural objects, and paints.

Figure 2 Colors used in the TM-30 calculations

These colors have been selected from a database of about 105,000 objects. In reducing that number to one that is more manageable, the authors of TM-30 made sure that the color samples were even distributed across the most modern color space (CAM02-UCS) and that their reflectances were evenly distributed across the visible spectrum, as shown in Fig. 3.

Figure 3 Spectral reflectances of the TM-30 color samples

Spectral tuning (gaming the system to achieve a higher score) isn’t possible with these color samples, which means that the resulting scores are honest, and comparisons of light sources are apples-to-apples.

Color Space

The second advantage of TM-30 is the selection of color space. A color space is a model of a range of possible colors. In our case we are interested in a color space that encompasses the entire range of visible colors. CRI uses a color space called CIE 1964 (U*, V*, W*), which is no longer recommended for any other use. In other words, it’s very outdated. TM-30, on the the other hand, uses the most up-to-date color space CAM02-UCS. TM-30 isn’t locked in time, either. There is a new, more accurate color space under discussion at CIE. If it is approved, and increases the accuracy of TM-30, I expect it would be included in a future update.

Reference Light Source

Like CRI, TM-30 uses Plankian radiation (blackbody radiator) for lower CCTs and the CIE Daylight (D) Series for higher CCTs for the reference light source. The difference is that CRI Ra has a pronounced shift at 5000 K from one to the other, resulting in the possibility of a significant shift in Ra values between 4999 K and 5001 K. TM-30 overcomes this by using a proportional blend of Plankian radiation and the CIE Daylight (D) Series between 4000 and 4999 K, much the way a variable white LED fixture blends LEDs of two different colors to achieve its full range.

Calculation Results

Instead of a single fidelity value, as with CRI Ra, TM-30 give us a wealth of data about the color rendering of the light source in question. The first is the Fidelity Index Rf. Like Ra, it is a comparison of the color rendering of the test light source compared to the reference light source. However, with 99 color samples it is a tougher test that cannot be gamed. I’ll have more to say about Rf in a future post.

The second is the Gamut Index Rg. Rg indicates the average change in saturation of the 99 color samples as rendered by the test source compared to the reference source. I’ll have more to say about Rg in the future, too.

So, from the start TM-30 gives us more information, but it doesn’t stop there. It also divides the color space into 16 wedges, called hue angle bins, as shown in Fig. 4. The Rf and Rg values of each bin are also calculated and reported so that if a specifier is interested in the performance of a light source in a particular color range, that information is available. The information is also presented graphically by showing the average shift of each bin on the same graphic.

Figure 4 TM-30 hue angle bins

In addition, if you really want to dig down deep, the TM-30 calculation tool calculates the Rf and Rg values of the individual 99 color samples.

What TM-30 Is And Isn’t

TM-30 is a calculation procedure that takes an objective and statistical approach to analyzing two aspects of color rendering – fidelity to a reference source, and saturation shift relative to the same reference source. The calculation also produces information about hue shift, which is presented graphically. The calculation procedure is a consolidation of years of research by individuals and organizations around the world. Its authors come from the research, specification,and manufacturing areas of the lighting industry. Research since its introduction in 2015 has supported its validity as an accurate method of characterizing color rendering. The CIE has endorsed Rf for scientific use in CIE 224:2017 Color Fidelity Index for accurate scientific use. Unfortunately, they declined to endorse it for specification or other uses, as I’ve discussed here. However, quite a few manufacturers see the advantage of TM-30 and are including Rf and Rg information on their cut sheets.

TM-30 isn’t a color rendering guide. It doesn’t contain recommendations for acceptable values. It reports calculated values and leaves interpretation of those values to the specifier based on experience and the particulars of the project. (However, the IES is likely to publish guidance in the future.) It also doesn’t attempt to evaluate color perception or color preference. Those two aspects of color are application (and even situation) dependent, so again the specifier will use experience and understanding of the project to determine what values are appropriate and/or acceptable.

TM-30 provides significantly more information about the color rendering of a light source, and the information presented is far more accurate than CRI. The authors of TM-30, and the IES Color Committee in general, are open to improvements in the calculation and the presentation of its results. As additional scientific information becomes available, or improved or expanded means of calculation and presenting information are developed, it can be updated as needed or on a regular three to five-year cycle.

Who’s Afraid of TM-30?

As the Co-Chair of the IES Color Committee, I have seen too many statements that full-scale adoption of TM-30 is too difficult and will create confusion in the market. Often, these assertions come from major manufacturers who want to control market disruption, not be disrupted. In my professional lifetime there have been, and continue to be, significant changes in the lighting marketplace. When new products are introduced, designers are told about the wonderful benefits of using them. There has never been a time when large manufacturers or organizations with loud voices have said the market could not accept about a new product because doing so was too burdensome. For example,

The introduction and transition to electronic ballasts and transformers meant that we had to learn about reverse phase dimming and control protocols.
The T5 lamp meant we had to change our layout patterns to accommodate lamps that weren’t standard 2’, 4’, and 8’ lengths.
Metal Halide lamps, especially PARS, meant that in exchange for energy savings we had to learn about the color rendering of a new type of lamp, and give up dimming.
Daylight harvesting and daylight responsive designs meant we had to learn about daylight zones, photosensors, and daylight harvesting control systems.
White LEDs meant we had to learn about another light source and its specific pros and cons, including different color rendering properties due to its SPD.
Circadian lighting means we are all in the process of learning how and when to apply the most current scientific evidence to certain project types. Since the science is constantly advancing on this topic, we must be aware and continue to educate ourselves.
Regularly updated energy conservation codes mean that as we begin to memorize the lower LPDs and changes to control and daylighting requirements, we have to relearn that information because it changes every three years.
Most recently, we’re supposed to enthusiastically embrace IoT, adding huge complexity to our lighting control systems and opening them up to hacking.

But, I keep hearing that industry adoption of TM-30, allowing specifiers to have a much clearer idea of the color rendering properties of their light sources, is tooo haaaaard! This is especially maddening when so many professions, including lighting design if you have an LC or LEED credential, require continuing education that is supposed to be more than halfway paying attention to a webinar.

Manufacturers love introducing and promoting new products and technologies that will expand profits, and specifiers get the hard sell all the time. But some manufacturers don’t want to consider TM-30 for several reasons. First, there’s the fear that the R_f value, which is analogous to CRI R_a, will be lower than the R_a value. Even though it’s a different, and tougher, test they fear loss of sales if numbers change. I suspect the manufacturers who fear this the most are those who have most engineered their spectra to score well on R_a, but know that R_f can’t be gamed in the same way. Second, as one manufacturer flat out told me, they’d rather put their money into IoT (and other new and profitable products) instead of updating cut sheets and web pages.

Here’s the thing – as a designer and specifier I have no interest in being stuck in 1965 (the year CRI was unveiled) or even 1995 (the most recent update to CRI). We know that CRI is flawed, we know what the flaws are, and we know that the CIE has been unable to come to consensus on fixing the flaws. The IES has done a great job of developing a new, accurate, modern tool that gives us so much more information than CRI ever could. My design decisions, and my ability to learn about my profession so I can be better at it, are not driven by manufacturer profit masquerading as manufacturers worrying about specifier or consumer confusion. Research over the past two years has shown TM-30 to be more accurate, and we continue to learn more about how to effectively use it. Lighting specifiers should begin the transition to TM-30 by insisting that manufacturers provide them with R_f, R_g, and color vector graphics.

R.I.P. CRI

It’s been a little over two years since the IES released TM-30-15 IES Method for Evaluating Light Source Color Rendition. In that time TM-30 has seen growing support in the industry and a growing body of evidence for its accuracy and usefulness. We’ve nearly reached the moment when we can all agree that it’s time to retire CRI and fully adopt a modern, accurate system of measuring and describing the color rendering of light sources. What’s wrong with CRI? Quite a bit, so if you’re not up to date on the issue here’s an overview.

In 1948 The CIE first recommended a color rendering index based on a method developed in 1937. The 1937 method is a fidelity metric (that is, it compares a test light source to a reference light source) that divides the spectrum into eight bands and compares each band to a full spectrum radiator. In 1965 the CIE finally adopted CIE 13-1965 Recommended method of measuring and specifying color rendering properties of light sources, based on a test color sample method, what today we call CRI R_a or just CRI. From the start it was apparent that there were problems. In 1967 a committee was established to correct for adaptive color shift. Other problems were uncovered, and in 1974 a formal update was published. Errors were uncovered in the 1974 edition, resulting in a third version in 1994, which is the version we use today.

So far, so good. Errors are discovered in the method used and are eventually corrected, so what’s the fuss? The fuss is that the corrections were minor compared to the scope of the errors, and 23 years after the last correction we still don’t have an accurate, up to date system. In the early 1990s a proposal to update the formula and test color samples failed to gain consensus. Two subsequent attempts to improve the metric also closed without adoption. The current problems, as described in the 2011 IES Lighting Handbook, 10th Edition include:

Averaging the color shifts of the eight test colors says nothing about the rendering of any single sample. A large error in one color can be masked by accurate rendering of the other samples.
The test color samples are all of moderate saturation so the index doesn’t reveal color shifts in saturated colors. In addition, the test colors are not evenly distributed through the color space or the spectrum, so light source spectra can be engineered to score higher than visual observation would indicate.
The color space used, the 1964 UCS chromaticity diagram, is no longer recommended for any other use.
All chroma shifts are penalized, even though research shows that moderately increasing chroma is desirable in many applications.
The chromatic adaptation used has been shown to perform poorly and is no longer recommended for any other use.
A single number index gives no information about the direction or extent of color shift for any particular color or color range.

Why haven’t these problems been corrected in the past 23 years? I’m told that there are two issues. The small issue is that competing scientific interests on the committee advocate new metrics that they’ve developed as a replacement or supplement to CRI. The larger problem is that manufacturers on the committee don’t want to see any changes that would reduce the CRI of any of their lamps. From their perspective, it’s better to have a high score on an inaccurate test than a low score on an accurate one. It seems that internal politics has been preventing updates, corrections, and improvements.

Although many other color rendering metrics have been proposed over the years, none has been adopted by CIE, which has the most significant voice on this issue. The result is that the sole internationally accepted metric, which has also been written into product specifications and into codes, is CRI. That began to change in 2015 with the introduction of TM-30. I’ll have more to say about TM-30 in future posts, but for now let’s agree that CRI R_a is broken and CIE is in no hurry to fix it. A better system exists, and our industry should adopt it.

The Myth of the Irrelevant Lighting Designer

Kevin Willmorth has a long and interesting article on his blog in which he argues for the recognition of professional lighting designers and what a professional lighting designer is and is not. The post echoes Chapter 1 of Designing With Light, and many of the things I’ve written here, including promoting the lighting design profession, the value of professional lighting design, the need for projects to use a professional lighting designer (here, here and here), those other than professional lighting designers making design decisions, and poor documentation of LED products by manufacturers, among other topics. I don’t have much to add to Kevin’s post, except to say that it’s well worth reading.

IES Lighting Terms and Definitions Now Online

ANSI/IES RP-16 Nomenclature and Definitions for Illuminating Engineering has long been one of the two major documents defining terms related to lighting design (the other is CIE ILV: International Lighting Vocabulary). RP-16-10 (the 2010 version of the Recommended Practice) is now available online as a searchable database. From the first page you can click on terms to see the definition and you can also search by keyword. If you don’t already own RP-16 bookmark this now!

IoT Lighting? No Thanks.

The current global cyber-attack, combined with last year’s “denial of service attack has me thinking about the lighting industry and IoT.

It was ironic that last year’s attack happened just days before the IES annual conference, at which IoT lighting was touted as the next big thing that everyone had to adopt or be left behind. You may recall that one aspect of that attack was that hackers recruited IoT devices like thermostats and smoke detectors. Many designers may think, “Well, sure, homeowners don’t have good security, but that wouldn’t happen to one of my corporate clients.” The current attack shows the flaw in that thinking. New tools have allowed hackers access to supposedly secure networks, and not all networks that should be secure (such as Britain’s NHS) actually are.

The question, then, is, “Why should my lighting system use IoT?” I’ve asked several friends in lighting design firms large and small and the answers I’ve received are revealing. Almost no one has a client who is asking for this. (I’ve had exactly one client who wanted the lighting system connected to the corporate LAN.) Do they want lighting systems connected to their BMS? If the client is knowledgeable and the building is large, yes, although today’s lighting systems have so many programming options we don’t need the BMS to control the lighting system. Do they want lighting systems to use Wi-Fi so that users can adjust the lights from phones and pads? Not very often. “Why would I want to give that many people authorization to change the lighting?” is the question asked, and rightly so. Do they want light fixtures with IP addresses and built-in Wi-Fi, Li-Fi, daylight sensors, occupancy sensors, temperature sensors, humidity sensors, and software that tracks shoppers or monitors space usage? “How much will that cost?” is the usual first question, followed by a strong “No.”

If we designers don’t see an artistic or operational advantage to these systems, and if our clients don’t see an advantage and aren’t asking for these systems, why all the noise about them? The answer, of course, isn’t better lighting design or increased energy efficiency, it’s money. Companies like Cisco see expanded profits from embedding Cisco sensors in every light fixture in a building, connecting all of those fixtures to Cisco POE switches and perhaps controlling the fixtures and sensors with Cisco software. Fixture manufacturers, always looking for a way to differentiate their products, jump on board. Marketing departments create hype, magazines and web sites need material, and voila! the next “must have” lighting system feature.

Who’s providing network security? The corporate IT department, I guess. Are the lighting systems vulnerable to hacking? The current and recent attacks tell us the answer is, “Yes.” Are manufacturers of IoT devices investing in security? Not really. They see it as the responsibility of someone upstream. Would anyone want a lighting system that is vulnerable to being turned off in an emergency, or reprogrammed by someone just to see if they can do it? No.

Some of the lighting systems I am designing are quite complex involving hundreds of fixtures with hundreds of addresses, multiple control protocols, and multiple points of control including touchscreens and Wi-Fi devices. One thing no one has to worry about, though, is high-jacking or corruption of the system. Each system stands alone. Software updates, if they are ever needed, are downloaded and installed via a USB key. Anyone wanting access to the system has to be within Wi-Fi range and has to hack the network. What would they get? Access to a single lighting system. There’s almost no reward and therefore there’s almost no incentive. Call me a Luddite if you like, but for now I’m going to stick to designing secure, flexible systems that provide my clients with only the features that they want at a price they are willing to pay. I’m sure that the pressure to “innovate” will eventually lead me to using these IoT systems. But for security’s sake I’m going to resist for as long as I can.

Design Guide for Color and Illumination

As the co-chair of the IES Color Committee I am delighted (pun intended) to announce the publication of the Design Guide for Color and Illumination. The guide is the result of over five years of work by more than a dozen researchers, engineers, manufacturers, and designers from across the globe. Here’s part of the description on the IES site.

Color can be described using concrete values such as chromaticity coordinates, spectral power distribution, or others discussed later in this guide. However, one’s response to color can be much more personal and emotional—and therefore more difficult to quantify. This guide takes the reader from basic vision and color vocabulary, through methods of measuring and quantifying color, and culminates in the practical use of commercially available white light and colored lights. The definitions, metrics, and references discussed will assist in building a critical understanding of the use and application of color in lighting.

It is probably the best, most thorough discussion of light and color available today. Everyone interested in color, color perception, color rendering, and their relationship to light should read it. It will be available at the IES booth at Lightfair.

Design Is A Process, Not Just A Product

I often tell my students that design is as much a process as it is a product. Even so, they (and some of my clients) sometimes want to go from first meeting to finished design in one step. I suppose one could do that, but the result wouldn’t be a thoughtfully appropriate design, it would just be fixture selection. The difference lies in the early part of the design process where we gather information about the project and the expectations of the stakeholders, followed by an analysis of that information towards the stated goals of the project. Only after completing those two critical steps can we begin the work of putting the design together and executing it. Here’s one way of looking at the entire process.

What Happened to IYL?

Elizabeth Donoff asks “International Year of What?” in her editorial in this month’s Architectural Lighting, and I have to agree with her. Early last year I noted that our professional organizations showed no plans to take advantage of the International Year of Light, and indeed nothing worth mentioning happened. The professional societies of the lighting community (IES, IALD, etc.) added the International Year of Light logo to their web sites, but that’s about all. They held no significant events, published no important documents, and made no efforts to raise the visibility of the profession with potential employers (architects and owners) or with the public at large. The IALD boasts that their regularly scheduled events were added to the IYL calendar, but say nothing as to what resulted, probably because the result was nothing. Lightfair 2015 was business as usual, I saw no recognition of IYL.

The entertainment industry did no better. United Scenic Artists Local 829, the union for theatrical designers, didn’t recognize the opportunities, nor did USITT, and at LDI (the entertainment industry equivalent of Lightfair) there was no sign that anyone knew about IYL.

As I’ve written before (see here and here, for example), and as many of us know, far too many projects are built with poor lighting because lighting design is seen as an added cost that can be avoided by having the architect, electrical engineer, or lighting sales person provide the “design” instead of a trained, professional lighting designer. Hoping this will change won’t change this. On an individual level, designers can educate their clients about the benefits of thoughtfully designed lighting, but it takes a larger, more expensive effort to reach those who don’t interact with lighting designers. Only manufacturers or professional organizations have the resources.

What could they have done in 2015, or what can they do this year? For starters, I’d like to see the IALD and/or the IES sponsor sessions on lighting design at the annual conventions of organizations such as AIA, ASID, and SCUP. Let’s get in front of the decision makers and teach them about what good lighting can mean to them. Topics such as energy efficiency, code compliance, and daylighting, as well as the more artistic and aesthetic sides of lighting design, are all appropriate and would, I think, be well attended. If we want lighting design to be seen as an integral part of any building project we have to work at it. Adding a logo to a web site isn’t enough.