{"id":1525,"date":"2021-03-01T10:14:43","date_gmt":"2021-03-01T15:14:43","guid":{"rendered":"https:\/\/designinglight.com\/?p=1525"},"modified":"2021-03-01T10:14:43","modified_gmt":"2021-03-01T15:14:43","slug":"its-time-for-a-unified-chromaticity-diagram","status":"publish","type":"post","link":"https:\/\/designinglight.com\/?p=1525","title":{"rendered":"It’s Time for a Unified Chromaticity Diagram"},"content":{"rendered":"\n

The pandemic has certainly distracted me from regular posting here.  I\u2019m probably not back to posting weekly, or even monthly, but I do have a new topic and a few things to say about it.  The topic is color science as it applies to lighting.<\/p>\n\n\n\n

No doubt you\u2019ve seen something like Figure 1 before.\u00a0\u00a0It\u2019s the CIE 1931 (x, y<\/em>) chromaticity diagram and is the most common graphic for showing the range of tunable white luminaires and LED colors and their color mixing possibilities.\u00a0<\/p>\n\n\n\n

\"CIE<\/a>
Figure 1 CIE 1931 (x, y<\/em>) Chromaticity Diagram<\/figcaption><\/figure>\n\n\n\n

The thing is, we keep using this diagram even though it has problems and has been replaced twice.\u00a0\u00a0The problem is that it isn\u2019t perceptually uniform, which means that the distance between any two color points doesn\u2019t correspond to the perceptual difference between those two colors.\u00a0\u00a0This was famously demonstrated in 1942 by David MacAdam.\u00a0Using 25 chromaticities he had a trained observer, using a device that allowed for the color adjustment of light, attempt to create a side-by side match from different starting points \u2013 for example match a yellow sample starting from green, then match it again starting from red, etc.\u00a0\u00a0When he plotted the results in CIE 1931 (x, y<\/em>) the area where color differences could not be detected formed an ellipse as shown in Figure 2.\u00a0\u00a0This demonstrated that the color space was not perceptually uniform.\u00a0\u00a0If it was the ellipses would have been circles.<\/p>\n\n\n\n

\"CIE<\/a>
Figure 2 CIE 1931 (x, y) Chromaticity Diagram with MacAdam Ellipses (at 10x size)<\/figcaption><\/figure>\n\n\n\n

These \u201cMacAdam ellipses\u201d have become the default way manufacturers talk about color consistency of their products.  You\u2019ll often see statements on cut sheets saying that the LEDs for a particular product line all fall within an X-step MacAdam ellipse (2-step, 3-step, etc.).  Want to hear something crazy?  In 2014, the International Commission on Illumination (CIE), which sets the standards for most things related to color and light, recommended ending the use of MacAdam ellipses.  Why?  Look at Figure 2 again.  The size of MacAdam ellipses changes as we move around the chromaticity diagram. So does anything related to them, such as Standard Deviation Color Matching (SDCM) another, although less common, measure.<\/p>\n\n\n\n

The first attempt to address the uniformity problem resulted in the CIE 1960 (u, v<\/em>) uniform chromaticity scale (USC) diagram (Figure 3).\u00a0\u00a0Correlated color temperature was originally calculated in the CIE 1960 (u, v<\/em>) UCS.<\/p>\n\n\n\n

\"CIE<\/a>
Figure 3 CIE 1960 (u, v<\/em>) Chromaticity Diagram<\/figcaption><\/figure>\n\n\n\n

It was later discovered that the CIE 1960 (u, v<\/em>) USC diagram also was not uniform.\u00a0\u00a0To improve uniformity the\u00a0v<\/em>-axis was scaled by 1.5, resulting in the CIE 1976 (u\u2019, v\u2019<\/em>) UCS diagram shown in Figure 4.\u00a0\u00a0As the most uniform UCS diagram, CIE 1976 (u\u2019, v\u2019<\/em>) is the one recommended for use when calculating or evaluating color differences, not CIE 1931 (x, y<\/em>).<\/p>\n\n\n\n

\"CIE<\/a>
Figure 4 CIE 1976 (u’, v’) Chromaticity Diagram<\/figcaption><\/figure>\n\n\n\n

Correlated color temperature was originally calculated in CIE 1960 (u, v<\/em>).\u00a0\u00a0However, since that diagram is no longer recommended for any purpose by the CIE, we use CIE 1976 (u\u2019, v\u2019<\/em>) but scale it back to CIE 1960 (u, v<\/em>).\u00a0\u00a0This is described as CIE 1976 (u\u2019, 2\/3 v\u2019<\/em>).<\/p>\n\n\n\n

The CIE\u2019s 2014 recommendation mentioned earlier replaced MacAdam ellipses with a circle in the CIE 1976 (u\u2019, v\u2019<\/em>) UCS.  A rough rule of thumb is that one MacAdam ellipse corresponds to a circle with a radius of 0.0011. Unfortunately, it doesn\u2019t seem that any manufacturers have made this transition.<\/p>\n\n\n\n

So, our industry is in a situation where we commonly use a 90 year old first generation diagram that was replaced 61 years ago.  We calculate CCT in a third generation chromaticity diagram that is 45 years old but tweek the math to refer back to a second generation 61 year old diagram.  It\u2019s crazy!  No other industry uses a system this convoluted.<\/p>\n\n\n\n

Why am I mentioning this?  I was recently reminded of a paper that was presented at last August\u2019s IES Annual Conference.  Presented by Michael Royer of Pacific Northwest National Laboratory, it proposed using the latest color science to make a fresh start with a single new chromaticity diagram that is very similar to CIE 1976 (u\u2019, v\u2019<\/em>) where we would calculate CCT, the color temperature bins for LEDs, color differences and the rest.  IES members can access the archived presentation after logging in to the IES website.<\/p>\n\n\n\n

Full disclosure, I\u2019m on the IES Task Group that is developing this new system.\u00a0\u00a0The Task Group is made up of people in academia, design, manufacturing and research from three countries.\u00a0\u00a0We\u2019ve refined our work since August and expect to publish these refinements soon.\u00a0\u00a0I encourage all of you to look for and learn about this proposal, to attend seminars when available, and to weigh in on this topic.\u00a0\u00a0Would our industry benefit from moving to a unified chromaticity system?\u00a0\u00a0Is this the right one?\u00a0\u00a0How do we educate specifiers and manufacturers?\u00a0\u00a0How do we phase in a new system?\u00a0\u00a0We can all have a voice in bringing the science we rely on into the 21st<\/sup>\u00a0Century.<\/p>\n\n\n\n

References<\/strong><\/p>\n\n\n\n

CIE. (2014). TN 001:2014 Chromaticity Difference Specification for Light Sources<\/em>. Vienna: International Commission on Illumination.<\/p>\n\n\n\n

CIE. (2018). CIE 015:2018 Colorimetry, 4th<\/sup> Edition<\/em>. Vienna: International Commission on Illumination.<\/p>\n\n\n\n

MacAdam, D. (1942). Visual Sensitivities to Color Differences in Daylight. Journal of the Optical Society of America<\/em>, 32(5), 247-274.<\/p>\n\n\n\n

Royer, M. et. al. (2020).  Improved System for Evaluating and Specifying the Chromaticity of Light Sources<\/em>. In: Illuminating Engineering Society Annual Conference 2020.<\/p>\n","protected":false},"excerpt":{"rendered":"

This post describes previous and current chromaticity diagrams for light and suggests the need for a new one.<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[12,18,19],"tags":[72],"class_list":["post-1525","post","type-post","status-publish","format-standard","hentry","category-color","category-design","category-lighting-profession","tag-color-science"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p4gZSw-oB","jetpack_sharing_enabled":true,"jetpack_likes_enabled":true,"jetpack-related-posts":[{"id":2434,"url":"https:\/\/designinglight.com\/?p=2434","url_meta":{"origin":1525,"position":0},"title":"Updating the CCT Calculation","author":"Jason Livingston","date":"March 8, 2022","format":false,"excerpt":"As I noted in Chapter 9 of the 2nd edition of Designing with Light, we calculate color temperature, correlated color temperature, and distance from the Plankian locus in a perverse way. \u00a0The calculations are performed in the CIE 1960 (u, v) chromaticity diagram (which is why distance from the Plankian\u2026","rel":"","context":"In "Calculations"","block_context":{"text":"Calculations","link":"https:\/\/designinglight.com\/?cat=6"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":4039,"url":"https:\/\/designinglight.com\/?p=4039","url_meta":{"origin":1525,"position":1},"title":"How are CCT and Duv Calculated? IES TM-40","author":"Jason Livingston","date":"September 30, 2024","format":false,"excerpt":"If you look up the definition of Correlated Color Temperature (CCT) in IES LS-1 you'll find, \"The absolute temperature of a blackbody whose chromaticity most nearly resembles that of the light source.\" \u00a0It seems straightforward. \u00a0The spectra of non-incandescent light sources don't exactly match a blackbody radiator. \u00a0They'll plot off\u2026","rel":"","context":"In "Color"","block_context":{"text":"Color","link":"https:\/\/designinglight.com\/?cat=12"},"img":{"alt_text":"C78.377 chromaticity quadrangles","src":"https:\/\/i0.wp.com\/designinglight.com\/wp-content\/uploads\/2024\/09\/3.8-C78.377-300x300.jpg?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":360,"url":"https:\/\/designinglight.com\/?p=360","url_meta":{"origin":1525,"position":2},"title":"With LEDs, Knowledge is Power","author":"Jason Livingston","date":"March 29, 2015","format":false,"excerpt":"I\u2019ve been hired to review an architect\u2019s lighting design and then design an appropriate control system. The fixtures selected are all LED products by a manufacturer that falls into the high-end residential\/economy commercial range of quality and price. The cut sheets are extremely frustrating. After nearly a decade of LED\u2026","rel":"","context":"In "Design"","block_context":{"text":"Design","link":"https:\/\/designinglight.com\/?cat=18"},"img":{"alt_text":"\"CIExy1931 MacAdam\". Licensed under CC BY-SA 3.0 via Wikimedia Commons - http:\/\/commons.wikimedia.org\/wiki\/File:CIExy1931_MacAdam.png#\/media\/File:CIExy1931_MacAdam.png","src":"https:\/\/i0.wp.com\/designinglight.com\/wp-content\/uploads\/2015\/03\/CIExy1931_MacAdam-271x300.png?resize=350%2C200&ssl=1","width":350,"height":200},"classes":[]},{"id":787,"url":"https:\/\/designinglight.com\/?p=787","url_meta":{"origin":1525,"position":3},"title":"TM-30 Rf: So Big, So Strong, So Smart!","author":"Jason Livingston","date":"November 6, 2017","format":false,"excerpt":"As we know, CRI Ra and TM-30 Rf are both measurements of color fidelity. \u00a0That is, they compare a test light source to a known reference light source and measure how well the test source matches the reference source. \u00a0One of the many shortcomings of CRI Ra is that it\u2026","rel":"","context":"In "Color"","block_context":{"text":"Color","link":"https:\/\/designinglight.com\/?cat=12"},"img":{"alt_text":"","src":"https:\/\/i0.wp.com\/designinglight.com\/wp-content\/uploads\/2017\/11\/CES-F32T8830.png?resize=350%2C200&ssl=1","width":350,"height":200,"srcset":"https:\/\/i0.wp.com\/designinglight.com\/wp-content\/uploads\/2017\/11\/CES-F32T8830.png?resize=350%2C200&ssl=1 1x, https:\/\/i0.wp.com\/designinglight.com\/wp-content\/uploads\/2017\/11\/CES-F32T8830.png?resize=525%2C300&ssl=1 1.5x, https:\/\/i0.wp.com\/designinglight.com\/wp-content\/uploads\/2017\/11\/CES-F32T8830.png?resize=700%2C400&ssl=1 2x"},"classes":[]},{"id":736,"url":"https:\/\/designinglight.com\/?p=736","url_meta":{"origin":1525,"position":4},"title":"A New Report on LED Color Shift","author":"Jason Livingston","date":"June 15, 2017","format":false,"excerpt":"Like other lighting technologies, the color or chromaticity of light emitted by an LED can shift over time. \u00a0To 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). \u00a0A new LSRC\u2026","rel":"","context":"In "Color"","block_context":{"text":"Color","link":"https:\/\/designinglight.com\/?cat=12"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":930,"url":"https:\/\/designinglight.com\/?p=930","url_meta":{"origin":1525,"position":5},"title":"Fixing CRI, But Not Really","author":"Jason Livingston","date":"February 5, 2019","format":false,"excerpt":"A couple of weeks ago the\u00a0Global Lighting Association\u00a0(GLA) published\u00a0Application of CIE 13.3-1995 with Associated CRI-based Color Rendition Properties.\u00a0\u00a0It proposes TM-30 like metrics to supplement CRI\u00a0Ra.\u00a0\u00a0Specifically, it proposes a color gamut index, Ga, that is similar to TM-30\u2019s Rg and a set of chroma indices, Ci, similar to TM-30\u2019s\u00a0Rch,hj.\u00a0\u00a0At first glance\u2026","rel":"","context":"In "Color"","block_context":{"text":"Color","link":"https:\/\/designinglight.com\/?cat=12"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"_links":{"self":[{"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/posts\/1525","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/designinglight.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1525"}],"version-history":[{"count":1,"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/posts\/1525\/revisions"}],"predecessor-version":[{"id":1530,"href":"https:\/\/designinglight.com\/index.php?rest_route=\/wp\/v2\/posts\/1525\/revisions\/1530"}],"wp:attachment":[{"href":"https:\/\/designinglight.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1525"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/designinglight.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1525"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/designinglight.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1525"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}