Hybrid Lighting Applications

Hybrid solar lighting (HSL) technology – a technology capable of collecting sunlight and distributing it, via optical fibers, into the interior of a building. This technology provides an exciting new means of reducing energy consumption while also delivering significant ancillary benefits associated with natural lighting in commercial buildings. Hybrid solar lighting has the potential to significantly reduce energy consumption for retailers while also maintaining, or exceeding, the lighting quality requirements of a retail environment. ORNL has been developing the fully integrated hybrid lighting system to provide the benefits of natural light (energy-savings and improved lighting quality) without the negatives associated with roof leaks and increased HVAC electricity loads. ORNL’s prototypes consist of three primary components, as illustrated in the above figure.

The sunlight collector consists of a large parabolic primary mirror and a segmented secondary mirror designed to focus the visible portion of sunlight into a bundle of plastic optical fibers. In addition to the mirrors, each collector includes two-axis tracking hardware, electronic tracking controls, optical filters, and mounting hardware for the mirrors and optical fibers. Each collector is mounted on a 4 inch schedule 40 pipe that penetrates the building roof, secured to the substructure, and is preferably centered above the 8 to 10 light fixtures to which it supplies light. Each light fixture consists of a traditional 2x4 foot light fixture containing 4 fluorescent lamps. The fixture is slightly modified to accommodate a sunlight diffusing rod (as shown in previous figure) that spatially distributes the sunlight similar to co-located electric lamps. A custom-designed control system and conventional electronic dimming ballasts are used to regulate the electric lights and reduce the electric lighting load. Each system covers approximately 1000 sq. ft. and is expected to displace approximately 2 kW of electric lighting. In addition to the energy savings, hybrid lighting offers other value propositions such as the potential of improved lighting quality and worker productivity, visual connection with the outside world, and the future possibility of increased sales. It will also reduce the roof penetration from 1250 to 50 linear feet and virtually eliminate additional HVAC loads attributable to skylights.

In commercial buildings, lighting consumes more electric energy than any other building end-use. Lighting one and two story buildings accounts for more than a quarter of all electricity consumed for commercial use in the United States. Typically, less than 25% of that energy actually produces light; the rest generates heat that increased the need for air-conditioning. Unlike conventional electric lamps, HSL systems produce little waste heat. Using sunlight directly avoid the conversion less of energy to illumination with the associated waste heat generation.

A collector focuses the visible portion of sunlight into an array of optical fibers while simultaneously converting otherwise wasted infrared energy into electricity

Hybrid light fixtures combine light from natural and electric sources to illuminate building interiors. Energy is saved because electric lights are dimmed in proportion to the amount of sunlight available

Flexible optical fibers efficiently pipe sunlight into buildings and route the natural light to multiple "hybrid" light fixtures

HSL delivers the benefits of natural lighting without the disadvantages of conventional daylighting technologies (such as windows or skylights). Although skylights have been around for many decades and function as a simple means of bringing natural light into a building, they can have a number of drawbacks that can limit their application. These can include:

- Significant source of heat loss or heat gain
- Can constrain design of building shape and orientation
- Difficult\Complicated to specify
- Point of condensation
- Uncontrolled, uneven illumination
- Susceptible to water leakage
- Susceptible to ventilation leakage
- Not appropriate for low ceilings
- Difficult to relocate or reconfigure
- Suitable for downlighting only (i.e. N/A to directional lighting or uplighting)
- Does not maximize the use of available sunlight
- A source of light pollution at night
- Cannot be easily turned off
- Security concerns

Hybrid Solar Lighting delivers natural light into a building interior without any of the above mentioned disadvantages.

Independent cost and performance models suggest the overall affordability of solar energy could be doubled or tripled using this new hybrid approach. The multidisciplinary R&D effort includes several industrial and university partners.

The future is bright for HSL. The nation-wide field trial program will provide system performance data and user-feedback essential for successful commercialization of the product. During the field trial program R&D will continue at ORNL in collaboration with industry and university partners to lower component costs, improve the longevity of the fibers, and advance the system control. New solid state lighting (LED) hybrid luminaries are also being pursued for increased energy efficiency. Exciting new areas of R&D for ORNL with industry and university partnerships include utilizing the HSL system for other technology applications including space heating, water heating, and hydrogen production, by transmitting the visible light and radiant UV and IR energy.

Melissa Voss Lapsa, Manager
Solar Technologies Program
Engineering Science & Technology Division
Oak Ridge National Laboratory
P.O. Box 2008, Building 5800
Oak Ridge, Tennessee 37831-6054
Phone: 865-576-8620
Fax: 865-576-0279

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Sponsor: DOE's Solar Technologies Program in the Office of Energy Efficiency and Renewable Energy

Extracted from "Science & Technology Highlights 2, 2000," published by ORNL's Energy Efficiency and Renewable Energy Program

Hybrid Lighting Promises Cool, Efficient Light and More...