THE NEW TM-30 metric for measuring colour is better than the standard colour rendering index, says the US government.
Scientists at the highly-respected Department of Energy have compared both systems and say that TM-30, which was developed by the Illuminating Engineering Society in 2015, is ‘more accurate with many sources’.
Members of the International Commission on Illumination, which developed the colour rendering index in the 1930s, have long acknowledged shortcomings with it for LED sources, especially in accurately characterising how a source renders saturated colours such as deep reds. But they have, at the same time, opposed alternatives such as TM-30.
Some experts believe the industry should move to the TM-30 two-metric standard that includes separate fidelity and gamut elements. But opponents have argued that the two systems return similar scores for commercially-available LED sources, making a move to TM-30 unjustified.
However, the Department of Energy research – written by Michael Royer of the Pacific Northwest National Laboratory – compares the colour fidelity metrics relative to a much larger sample of LED sources than have been considered before.
In the case of the commercially-available sources, the tests revealed a high degree of correlation between the rival methodologies. But the other sources tell a different story. Sources with colour rendering index of 80 were found to range in TM-30 fidelity values from 50 to 86.
Of course, one could argue that the commercially-available sources are what really matters. That sample set is dominated by fluorescent, incandescent, and high-intensity discharge lamps, along with LEDs based on relatively-simpler phosphor compositions.
But the LED industry is increasingly seeing novel approaches to phosphor-converted LEDs, some which use three-phosphor mixing to improve the reds.
Premium lamp maker Soraa has long used a three-phosphor mix with a violet emitter. CRI Ra penalises such sources for rendering more saturated reds — a preferred outcome in most cases.
- The design of LED luminaires is the subject of this year's Lighting Fixture Design Conference, which takes place on 20 and 21 June 2018 . Organised by Lux and LEDs magazine, the event takes place at the Cavendish Conference Centre in London. For more information and to reserve you place, click HERE.