Big Guys Finally See the “White”

Soraa Chief Technology Officer Mike Kramer shares insights on whiteness rendering in this blog article.

Soraa Chief Technology Officer Mike Kramer. (Source: Soraa)

More than one year after Soraa demonstrated it (see my blog from 5/6/13), the importance of whiteness rendering is now being noticed by the larger lighting manufacturers. Perhaps the most notable imitation, from Philips (see LEDs Magazine July/Aug 2014, pp. 9-10), mixes in some violet-emitting with blue-emitting LEDs to provide a level of Optical Brightening Agent (OBA) excitation, which is necessary for whiteness rendering.

Unfortunately this approach does not address the typical color rendering problems associated with blue-based LED sources, including blue overshoot and a lack of cyan and red content. The resulting, and fairly bumpy, spectrum is shown below, in comparison to Soraa VIVID and to a reference (blackbody) illuminant.

Soraa Vivid v.s. Philips Crisp White. (Source: Soraa) 

Indeed, inferior color quality in the mixed violet/blue approach is immediately recognized when measured with newer color rendering metrics, such as NIST’s Color Quality Scale (CQS), as shown in the color charts below. The hue distortions—excessive yellows and blues, dull reds and greens—are clearly observed. (The reduced color quality is also predicted by simply looking at R9: 95 for VIVID, ~50 for Philips.) Finally, the Philips LED targets an off-Planckian white point to mimic the pinkish light characteristic of ceramic-metal-halide discharge lamps (CMH or CMD), while the Soraa VIVID spectrum is exactly on the blackbody curve and designed to give accurate and natural color rendering.

Soraa Vivid v.s. Philips Crisp White CQS. (Source: Soraa) 

Finally, there are a few misleading comments and/or errors in the LED Magazine article that I feel compelled to address:

1) Contrary to what is stated, the short wavelength emission in the Philips LED is not “deep blue”; at 410 nm it is deep in the violet (even more so than for Soraa);

2) High R9 light sources do not give “reddish to yellowish” appearances to white or light colors (see CQS charts, above); and

3) Regarding efficiency, one cannot compare chip-on-board (COB) LEDs of different sizes; a comparative estimate based on Soraa’s 8.5 mm COB (for AR111 and PAR 30/38 lamps) suggests Philips 9 mm would need to overcome an efficiency gap of about 20% in order to match Soraa’s light output and color characteristics—very tough given Soraa’s superior GaN-on-GaN technology.

For the consumer it is a good thing that quality of light (for rendering whites as well as colors) is catching on. With the big guys taking notice, hopefully it will be easier for standards to be set that ensure natural, high quality lighting is available for our future.

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