Goleta-based Kaai has raised a $3.5 million series B round of financing from a group of investors that includes clean-tech investment firm Khosla Ventures, according to regulatory filings.

The secretive start-up is working on an LED lighting technology developed by Steven DenBaars and Shuji Nakamura, two researchers at the University of California, Santa Barbara. Nakamura is widely regarded as the inventor of white and blue LEDs.

Kaai raised a first round of $5 million in 2008, according to regulatory filings. The company, based on Pine Avenue in Goleta, has not made any public announcements, and neither Kaai nor Khosla responded to requests for an interview.

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