Mirrored Light Pipes
Building Core Lighting: Daylight or Single Lamp Serving Multiple Luminaires vs. Electric Lighting
Reflective pipes, some using total internal reflection (TIR), that convey light from exterior daylight collectors to locations within a building where it is needed, possibly to fixtures that also have electric lamps.
Item ID: 118
Technical Advisory Group: 2009 Lighting TAG (#1)
Technical Advisory Group: 2014 Commercial Building TAG (#9)
Average TAG Rating: 2.55 out of 5
TAG Ranking Date: 03/17/2014
TAG Rating Commentary:
- Potentially very useful but in more limited applications. Needs collection optics that are not mentioned here. Could be used in plenum spaces. Cost is an issue and lighting savings require dimming ballasts to work .
- I think this refers to Tubular Daylighting Devices (TOO) which is officially a daylighting system, with wide distribution and great potential. The key to their success is the integration with electric lighting to realize savings. CLTC is working on advanced versions that also manage the daylight penetration for optimized daylight harvesting. The operation is integrated with the electric lighting controls, using the same photo sensors to control both systems. I definitely support this technology and look forward to taking it to the next level.
- How new is this?
- Application may be limited, installation difficult in existing buildings
Mirror light pipes are commercially available and can be used to provide daylight to the interior of buildings where windows and skylights are non-existent, unsuitable, insufficient or generate too much heat gain. Light pipes are also used with tubular skylights and high-wattage sulfur lighting systems to distribute light throughout a building space.
A light pipe system is typically made up of three components: a round dome or Fresnel lens that collects as much sunlight as possible from all angles while blocking out harmful UV rays, a highly reflective tube, and a diffuser to spread the light from the tube around the room and prevent "hot spots" and glare from occurring. Multiple reflections occur within light pipes to maximize the amount of light that is delivered to the building’s interior, but a light pipe cannot distribute more light than it collects. Light pipes with larger diameters should be used whenever possible to maximize the amount of light that is successfully transmitted and distributed. When long, narrow light pipes with many bends are used, the amount of light that is transmitted is reduced.
Light pipes are ideal for use in hazardous or dangerous locations because they pose no fire risk. They are passive lighting devices that use no electricity. Energy savings depend on building space occupancy and lighting requirements, the wattage of the conventional or alternative lighting system, and the number of hours that the conventional system can be turned off when natural light is available. Potential drawbacks include the cost of the light pipe system and the loss of lighting in a large area of the building if the system fails. Conventional lighting systems in buildings requiring lighting after dark so redundant lighting sources with associated controls are required.
Baseline Description: Standard office lighting
Baseline Energy Use: 2.7 kWh per year per square foot
The baseline value is based on office lighting, with a baseline of the Washington non-residential energy code standard of 0.91 W/sf, in office lighting, operating 3000 hrs. per year.
Manufacturer's Energy Savings Claims:
Currently no data available.
Best Estimate of Energy Savings:
"Typical" Savings: 53%
Energy Savings Reliability: 2 - Concept validated
Mirrored pipes theoretically use no energy. The 53% reduction in lighting energy use is consistent with the use of a photocell daylighting (dimming) system installed in the perimeter zone of a commercial office building (See Page 59 of SMUD's "Advanced Sidelighting Products" report dated December 14, 2012) (Tim Perry, 12/14/2012). This technology must be used in conjunction with a daylighting/photocell system to obtain the desired energy savings.
Energy Use of Emerging Technology:
1.3 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
This technology could technically be used for virtually any commercial building, since this includes solar tubes, but it probably will mainly be of interest to owners/operators of commercial office buildings. The 2009 Commercial Building Stock Assessment (CBSA) indicates a total regional office building square footage of 510 million sf. (NEEA, 2009) It is assumed that only a small portion of the interior space of an office building (perhaps conference rooms, lavatories, reception areas and hallways) would be illuminated by light pipes. For multi-story buildings, cost effectiveness would suffer if light pipes were extended down to lower floors. Losses within the light pipes would also increase. For these reasons, it is assumed that 5% of the commercial office floor space would be a viable candidate for this technology.
Regional Technical Potential:
| || Total Commercial Floor space || % Applicable || Applicable space |
| Source, units || (NEEA, 2009) (s.f.) || WSU EP estimate || (s.f.) |
| || 510,000,000 || 5% || 25,550,000 |
0.04 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Currently no data available.
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.