Research Papers

Design and Development of a Fiber-Optic Hybrid Day-Lighting System

[+] Author and Article Information
Sean Lawless

Steven Winter Associates, Inc.,
61 Washington Street,
Norwalk, CT 06854
e-mail: Seanl320@yahoo.com

Ravi Gorthala

Mechanical Engineering,
University of New Haven,
West Haven, CT 06516
e-mail: rgorthala@newhaven.edu

1Corresponding author.

Contributed by the Solar Energy Division of ASME for publication in the JOURNAL OF SOLAR ENERGY ENGINEERING: INCLUDING WIND ENERGY AND BUILDING ENERGY CONSERVATION. Manuscript received June 13, 2017; final manuscript received January 7, 2018; published online February 20, 2018. Assoc. Editor: Ming Qu.

J. Sol. Energy Eng 140(2), 021012 (Feb 20, 2018) (8 pages) Paper No: SOL-17-1228; doi: 10.1115/1.4039024 History: Received June 13, 2017; Revised January 07, 2018

The primary objective of this study was to develop a fiber-optic hybrid day-lighting system for mobile application such as military shelters in order to cut energy use and the use of fossil fuels. The scope included the design, development, and testing of a hybrid lighting system that is capable of producing about 16,000 lm output with design challenges including light-weight, compactness, and optics that can tolerate a high tracking misalignment. The designed system is comprised of two subsystems: the solar collector and the solar hybrid lighting fixture (SHLF). The solar collector, consists of a housing, a structural stand (tripod), a dual axis tracking system, Fresnel lenses, secondary optics, and fiber-optic cables. The collector is a telescoping aluminum box that holds eight 10-in diameter Fresnel lenses, which focus sunlight onto eight secondary optics and deliver uniform light to the fiber-optic cables. The secondary optics have filters to block UV/IR. The optics has been designed to have a high half-acceptance angle of 1.75 deg and can accommodate a tracking accuracy of 1.50 deg or better. This novel SHLF consists of two components: a solar fiber-optic system and a light emitting diode (LED) system. The fiber-optic cable is coupled to an acrylic light diffusing rod that delivers the sunlight into the room. During sunny periods, the solar fiber-optic lighting could provide full illumination level. In order to keep the same level of lighting during cloudy periods, the LED portion of the light fixture can supplement the output of the SHLF. A compact, light-weight prototype system was built and tested. The results showed that the system's output per lens for the 20 ft cable was about 1750±50 lm at a global solar illuminance of 115,000 lx. The total system was capable of delivering 14,000 lm of sunlight.

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Fig. 1

A schematic of the overall solar hybrid lighting system

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Fig. 2

An arbitrary shaped concentrator

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Fig. 3

Ideal geometric concentration factor as a function of inlet half-angle of acceptance

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Fig. 4

Edge-ray tracing for a single-lens concentrator

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Fig. 5

Edge-ray tracing for a dual-lens concentrator

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Fig. 6

An acrylic conical/CEC secondary lens

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Fig. 7

Optical silicone test lenses

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Fig. 8

Thermal analysis of the secondary lens holder

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Fig. 9

Secondary lens and lens holder prototypes

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Fig. 10

Index matching gel applied on fiber-optic cable

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Fig. 11

A photo of the collector housing: (a) version 1 and (b) version 2

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Fig. 12

Photos of tripod prototype

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Fig. 13

Heliotrack sensor (left) and controller (right) optic cable

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Fig. 14

A photo of the tip-tilt dual-axis tracker

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Fig. 15

A photo of the azimuth-altitude tracker modified for the prototype

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Fig. 16

The solar hybrid light fixture

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Fig. 17

Testing of SHLF in a 2 m integrating sphere

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Fig. 18

Testing of SHLF with handheld light meter 18 in away

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Fig. 19

An IR image of the fiber-optic cable face

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Fig. 20

An integrating sphere for measuring fiber-optic light output

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Fig. 21

Light output from various fiber-optic cable lengths (experimental versus theoretical)




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