Sir Richard Branson, the British adventurer and entrepreneur extraordinaire, is making his second major green-technology investment in less than a month.

Branson's venture capital firm Virgin Fuels, along with Gemini Israel Funds, Israel Cleantech Ventures and Israeli investor Altshuler Shaham, is injecting $9 million into Metrolight Inc., a Brentwood, Tenn., maker of smart electronic ballasts for high-intensity discharge lamps.

High-intensity discharge, or HID, lamps are nothing new. In fact, 22% of all lights in the world are estimated to be HID lights. They are mostly used to brighten large spaces, and can be found everywhere from street-lighting to factories to big-box retailers. What Metrolight does is take this existing technology and make it longer-lasting and energy efficient.

"Metrolight's products help customers reduce up to 65% of lighting energy costs, double lamp life, drastically reduce maintenance costs and take full control of their lighting systems," according to a company press release.

Virgin Fuels' investment in Metrolight is another step in Branson's effort to rebrand himself as the patron saint of green investing. In 2006, he invested $400 million in Virgin Fuels. He also pledged to donate all profits from his various transportation businesses to the effort to fight global warming -- an amount that could exceed $3 billion in 10 years.

According to Shai Weiss, managing partner of Virgin Fuels, Metrolight is a good choice for its growing portfolio of diversified green technology investments.

"Our sweet spot is with investments that are ready for growth and expansion and with products that have a short time to market, rather than early-stage technologies," Weiss says. "Metrolight fits this model perfectly."

Metrolight has been operating in the U.S. lighting business since 2002. It started out working with end users of its electronic ballasts to generate demand for its product. Now it's beginning to see a flood of interest from OEM distributors, as well.

"There is currently very little competition in high wattage," Executive Vice President Randy Reid.Reid says. "That is why this investment by Virgin Fuels is so important. Demand for electronic HID is coming at us like a freight train."

Ballasts are devices that get HID lamps to light up. They traditionally work through a magnetic system that sends a large surge of electricity through the lamp's innards. Metrolight's ballasts use less electricity at a much higher frequency than normal ballasts. This reduces the wear and tear on the devices, making them last considerably longer than other HID lamps.

"Our HID lamps love the way they are treated," Reid says.

Metrolight's ballasts can be controlled by analog devices like motion sensors so that HID lamps turn on and off when needed. They can also be controlled via digital software, giving customers complete interactivity over when and how their lighting systems are used.

Major energy savings can be achieved just by raising and lowering light levels as needed throughout the day. Outdoor light systems on streets and in parking lots are mostly "dumb" with only on and off states. Parking lot lights managed by Metrolight ballasts could keep the lights dim unless cars are entering or exiting, potentially generating significant cost savings for their owners.

While HID lamps fitted with Metrolight's electronic ballasts cost more up front than traditional magnetic ballasts, they usually pay for themselves in about two years with the energy savings that they bring, according to Reid.

Another benefit of Metrolight's products concerns their failure and disposal. HID lamps have had an end-of-life problem because they can explode. Most all lamps, including HID and fluorescent, contain mercury, which is harmful for the environment if it is disposed of improperly.

Metrolight's solution to this problem is to monitor their lamps' activity so that they shut down before they fail. Also, Metrolight's lamps last twice as long as traditional HID lamps, and they can be recycled once their lifespan has ended.

The company competes with giant bulbmakers Philips ( PHG) and GE ( GE), but Metrolight is preparing to make a major push into the global lighting market. It hopes to use its relationship with Virgin Fuels to energize the initiative.

As part of the investment, Weiss will be joining Metrolight's board. "His team tends to immerse itself in the businesses that it invests in, which will be very helpful for us," Reid says.

Also, Virgin's horizontal combination of businesses that span the globe has lots of facilities that need lighting. "Virgin will become an instant customer," Reid points out.