{"id":769,"date":"2017-10-16T10:00:51","date_gmt":"2017-10-16T14:00:51","guid":{"rendered":"https:\/\/designinglight.com\/?p=769"},"modified":"2017-10-16T07:53:17","modified_gmt":"2017-10-16T11:53:17","slug":"r-i-p-cri","status":"publish","type":"post","link":"https:\/\/designinglight.com\/?p=769","title":{"rendered":"R.I.P. CRI"},"content":{"rendered":"

It’s been a little over two years since the IES released TM-30-15 IES Method for Evaluating Light Source Color Rendition<\/em>. \u00a0In that time TM-30 has seen growing support in the industry and a growing body of evidence for its accuracy and usefulness. \u00a0We’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. \u00a0What’s wrong with CRI? \u00a0Quite a bit, so if you’re not up to date on the issue here’s an overview.<\/p>\n

In 1948 The CIE first recommended a color rendering index based on a method developed in 1937. \u00a0The 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. \u00a0In 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<\/em>, what today we call CRI R<\/em>a<\/sub>\u00a0or just CRI. \u00a0From the start it was apparent that there were problems. \u00a0In 1967 a committee was established to correct for adaptive color shift. \u00a0Other problems were uncovered, and in 1974 a formal update was published. \u00a0Errors were uncovered in the 1974 edition, resulting in a third version in 1994, which is the version we use today.<\/p>\n

So far, so good. \u00a0Errors are discovered in the method used and are eventually corrected, so what’s the fuss? \u00a0The 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. \u00a0In the early 1990s a proposal to update the formula and test color samples failed to gain consensus. \u00a0Two subsequent attempts to improve the metric also closed without adoption. \u00a0The current problems, as described in the 2011\u00a0IES Lighting Handbook, 10th Edition<\/em> include:<\/p>\n