Soraa re-asserts the virtue of high colour quality in LEDs
Other manufacturers are beginning to see the 'white'
More than a year after Soraa demonstrated the importance of whiteness rendering in LED lamps, the topic is being noticed by the larger lighting manufacturers, according to a recent blog by Soraa's chief technology officer Mike Krames.
Philips is a notable new arrival: it is mixing violet-emitting with blue-emitting LEDs to provide a level of Optical Brightening Agent (OBA) excitation, which is necessary for whiteness rendering.
Inferior light quality holds back sales of many LED-based replacements for halogen lamps in casinos, hotels, high-end retailers and cruise ships. Soraa, a start-up based in Goleta, California, has targeted this area with a novel chip that features in its solid-state replacement for 50-75W halogen lamps.
Soraa's lamps produce a full-colour spectrum by pumping red, blue and green phosphors with a violet-emitting chip. In contrast, most white-light sources employ a blue LED to excite a yellow phosphor, which is sometimes combined with a red variant. According to Soraa, when you excite with a blue LED, it is not possible with a phosphor to tune the light down to violet, so typical competitor products are missing the violet all together. This omission makes a big difference to the appearance of anything containing whiteners, which are excited by violet light.
Philips, by mixing in some violet-emitting with blue-emitting LEDs, does not completely address the colour rendering problems associated with blue-based LED sources, says Krames. These problems include "blue overshoot and a lack of cyan and red content." The resulting spectrum is shown above, in comparison to Soraa VIVID and to a reference (blackbody) illuminant.
Newer colour rendering metrics, such as NIST's Color Quality Scale (CQS), as shown in the colour charts below, reveal the colour quality in the mixed violet/blue approach better, says Krames, including the hue distortions. Krames adds that 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 colour rendering.
Krames concludes: "For the consumer it is a good thing that quality of light (for rendering whites as well as colours) 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."
Founded in 2008, Soraa has pioneered lamps using LEDs built from pure gallium nitride substrates (GaN on GaN).
