Have you ever walked inside a large retail store on a sunny day, looked up at the ceiling, and wondered why an arsenal of florescent lights is eating through kilowatts of power when natural sunlight could do the same job for free?
Lighting accounts for about a third of all electricity consumed in US commercial buildings. It has long been known that substantial energy reduction can be realized by replacing artificial light with natural light. However until recently, the only day-lighting technology available was the skylight. Skylights suffer from limited intensity, inability to spotlight, and lack of consistent illumination on overcast days and at night. In addition, since skylights allow infrared radiation to enter the building envelope in the summer peak cooling period, better HVAC efficiency can be obtained using well-shaded windows for day-lighting. Finally, if installed carelessly, skylights leak.
A team of researchers at Oak Ridge National Lab (ORNL) is taking a new technology, fiber-optics, and putting an even newer spin on it. Utilizing rooftop-mounted parabolic solar collectors reminiscent of satellite dishes, these researchers focus natural light onto a bundle of 127 optical fibers. These flexible fibers then transmit the gathered light throughout the building, around corners and between levels, to where it is needed.
Completing the evolution away from skylights, steady illumination is achieved using a hybrid fixture. As reported in a Discover Magazine article, “Let the Sun Shine In”, the sunlight-bearing fiber optics are integrated into a fluorescent light fixture with a built-in dimmer. As the intensity of piped-in sunlight drops, the fixture compensates by increasing the fluorescent bulb output to maintain uniform illumination through the day.
Based in Oak Ridge, Tennessee, Sunlight Direct, LLC, is now commercializing hybrid lighting. A short video from Solar Direct entitled “Hybrid Solar Lighting” highlighting their product lines can now be viewed on You Tube. Aiming for commercial production in early 2008, Sunlight Direct, LLC currently has 25 hybrid lighting systems installed across the US for testing. These systems are built around a 1200-mm-diameter solar collector, which actively tracks the sun. One collector connected with 8 to 10 hybrid light fixtures can illuminate about 1000 square feet.
Sunlight Direct estimates that on a sunny day one of its hybrid lighting fixtures will deliver 50,000 lumens, equal to 55 60-watt incandescent lamps. ORNL estimates that in the nation’s sunbelt, lighting energy savings of 6000 kWh per year can be obtained by each solar collector. Since the optical fibers filter heat-carrying infrared light, an additional energy savings of as much as 2000 kWh per year is possible by reducing building cooling load.
In the You Tube Video, Sunlight Direct estimates a target price point of $10,000 per collector. Under this pricing in an area with $0.10 kWh electricity, the hybrid light fixtures have a simple payback of about 12.5 years. In the spectrum of building technologies, this return on investment duration puts hybrid lighting fixtures on-par with conventional photovoltaic panels.
As an additional economic bonus, Sunlight Direct cites a number of studies indicating that human performance and product sales are enhanced under natural lighting. Unfortunately, I am an engineer, not a psychologist. So I will leave evaluation of the psychological impacts of this technology to my friends in the social sciences.