Earlier this month, VC- and strategic-funded Crystal IS was acquired by the Asahi Kasei Group, a manufacturer of compound semiconductor devices. Crystal IS is developing ultraviolet light-emitting diodes on aluminum nitride substrates for germicidal water applications. Crystal IS has been in development mode for over a decade with technology spun out of Rensselaer Polytechnic Institute in Troy, New York.

Short wavelength UV light below 280 nanometers (C-band) interferes with DNA repair in bacteria -- and renders water free of live bacteria.

The output from solid-state UV-C light sources remains modest compared to the traditional sources, such as high-intensity discharge lamps. So at the moment, UV-LEDs from Crystal IS and others like SETi are limited to light pens and appliances for consumer water sterilization and fall short of the wattage outputs needed for industrial and municipal water treatment applications.

Crystal IS received venture funding from ARCH Venture Partners, Lux Capital, the Credit Suisse/New York State Common Retirement Fund, Harris & Harris Group, and strategic investment from Asahi Kasei Group and San'an Optoelectronics Company.

IPOs of VC-funded greentech firms are far less common than investors would prefer. Those greentech firms that have made it through the IPO window such as Tesla Motors, A123 and the thinly traded Khosla biofuel firms are not close to profitable.

Perhaps the imminent Facebook IPO will provide some momentum for greentech IPO aspirants such as BrightSource Energy and Enphase. Whether those firms are destined for greatness is another story.

In the meantime, venture investors will have to content themselves with mergers and acquisitions.

Josh Wolfe, an investor at Lux Capital, told me that the exit was at "a nice multiple."

Financial details of the deal were not disclosed.

But Harris & Harris Group (NASDAQ: TINY) was an investor in Crystal IS, and because they are a publicly held firm, they had to publicly disclose their return on the company. A press release on their website, since redacted, read "Between 2004 and 2009, Harris & Harris Group invested approximately $1.75 million in Crystal IS. As of September 30, 2011, Harris & Harris Group valued its shares of Crystal IS at $0. On December 28, 2011, Harris & Harris Group received a portion of its payment of approximately $1.74 million in cash. Another approximately $288,000 is being held in escrow for a period of 15 months." Here's a link to the now-edited release.

That would appear to be a break-even return, at least for Harris & Harris.