Tech Note: Light Shelves

December 12th, 2009

A surprisingly effective way to draw light into a room is by use of a light shelf. These horizontal reflectors are mounted either inside, outside, or on both sides of a southerly-facing window. Sunlight bounces off the surface and onto the ceiling within.  Any bright surface will diffuse daylight effectively.

In my office though, I experimented with a pair of Ikea mirrors for more interesting light play. They’re mounted face up about 9″ down from top of glass, comfortably above eye level. The underside is painted white, to serve as a mini “ceiling” to the light reflected up from the venetian blinds below.

Mirrored light shelves reflecting sunlight onto ceiling

Mirrored light shelves reflecting sunlight onto ceiling

My office ceiling is the underside of a 12-in-12 pitched roof; the exposed surface is a dark grey polyiso insulation with merely a thin coat of white primer. Even so, the reflected sunlight on a clear day (center image, below) is roughly 2.5 times brighter than a pair of T-8 fluorescent tubes (right). Compare this to the ambient light of the ceiling — from light shelves reflecting the surrounding sky (left). Note that readings (in footcandles) are taken 12″ from the ceiling to isolate the light source for the meter.

Light readings for ambient, reflected sunlight, and dual T-8 fluorescents

Light readings for ambient, reflected sunlight, and dual T-8 fluorescents

In another project I inverted the concept, reflecting low winter sun down through skylights. Here the reflectors act to shade the skylights during the summer months. Specifics of this project are spelled out here.

South-facing, inverted reflectors over skylights to catch winter sun

South-facing, inverted reflectors over skylights to catch winter sun

For retrofitting windows, an interesting product called LightLouver based on the same principle as the light shelf has been developed as a vertical window treatment. I haven’t seen this in person, though, and don’t know how it compares to a standard polished chrome venetian blind.

4 Responses to “Tech Note: Light Shelves”

  1. 1 Bruce Gold
    January 4th, 2010 at 12:53 pm

    My company manufacturers Interior and Exterior Light Shelves. We have found that a radius design far surpasses the performance of a flat shelf. In an interior flat shelf application, the light(as your application also demonstrates) reflects at an inverse angle from the way it enters the space. With a radius design, you get the light refracting at multiple angles and with deeper penetration into the interior of the room. The cost of the much larger (48″ to 72″) projection of the radius design over the flat shelf (18″ to 24″) is slightly higher (about 10 – 20%)but the performance is better allowing for less artificial lighting offsetting the cost. On the exterior, the same holds true for the radius as it reflects more light into the space, drains water better, and helps minimize drift loading. I applaud your research and would like to discuss your findings.

  2. 2 Daphne Sidaway-Wolf
    April 19th, 2010 at 1:22 pm

    Hi Bruce,
    Our Innovation and Climate Action Branch in the British Columbia Minsitry of Agriculture and Lands is moving into a large area, with one wall on which there are windows. I am looking at the light shelf concept and am intrigued by your comment about higher performance of the radius design. Since our building is rented, an interior light shelf woudl be the only one we could install. What is your company’s name and where are you located?
    Thanks very much,
    Daphne Sidaway-Wolf
    250 356-2945

  3. 3 Geof
    April 23rd, 2010 at 5:03 pm

    Allow me, Bruce: He’s at Good luck,

  4. 4 Jeffrey
    June 11th, 2010 at 2:26 pm

    Nice. It’s amazing how light can transform a room – connect it to the outside world, and let the changes in the sky vary the mood in the room. There’s nothing like sunlight.

    Cool photos.

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