While lighting controls and sensors help reduce the amount of artificial lighting used in commercial buildings, “Sunlight harvesting” has the potential to advance commercial-building energy performance and livability to a higher level. Rather than ignoring or blocking out sunlight, sunlight harvesting puts sunlight to use – turning office windows into powerful and effective light sources. Satisfying more of our buildings’ lighting needs with harvested sunlight can simultaneously save owners money, lessen our environmental impact, and make more comfortable, productive interior spaces.

Even with its many benefits, and despite the presence of sunlight harvesting in 1970s and 80s design, the practice is unknown in contemporary domestic construction. In order to reintroduce some of this knowledge to the local community, I have worked with RetroSolar, a German blinds manufacturer, to create a sunlight harvesting demonstration in the offices of a local law firm.


The technique is simple. Direct sunlight contains an order of magnitude more visible light than that emitted from the open sky. Anyone who sits at a desk under even a modest sunbeam understands this all too well. It is too bright, and to make the workspace usable the blinds must be lowered, ironically forcing the use of artificial lighting. Sunlight harvesting places reflectors at the window to catch the sunlight and direct it upward and inward. This shades glare and redirect all that intense lighting power to the ceiling, where it spreads out evenly, just as an overhead light does. Utilizing “specular” mirrored reflecting surfaces provides unusually deep transportation of the light into the typically unlit office interior – think of the distance one can reflect a beam of sunlight using a hand-held mirror, in contrast to what is possible with a sheet of white paper.


These reflectors can take a number of forms, including lightshelves, fixed or adjustable louvers, or even micro-prismatic adhesive films, and need to be designed in response to the sun angles of a window’s orientation. One of the most promising light harvesting tools are polished aluminum venetian blinds with upturned slats. These blinds provide the benefits listed above without the cost or disturbance of more elaborate construction. RetroSolar’s line includes a wide range of highly sophisticated products that elegantly fold and wrinkle the basic curve into a palette of shapes that harvest or reject sunlight in varying proportion, as needed. They have kindly offered two sample blinds for this demonstration. The Flex80, installed in a south-facing office, has fine ribbing to create a Fresnel effect which rejects much of the incident sunlight back outside. The Lux model, placed in a West-facing office, combines a curve with a W-shaped fold. It harvests the majority of incoming sunlight.


The blinds have only been in place for a few weeks, so it is too soon to make any definitive report, but so far I am impressed by how far they throw the light! With the right tilt setting, sunlight was reflected across the ceiling as far as a dropped soffit at the building core – easily 30 feet!

We intend to keep them up for approximately a year – so stay tuned for more information!

Guest Blog written by:
Ryan Enschede
Ryan Eschede Studio
Sustainable Architecture

Want the latest news from Building Energy Exchange?

Sign Up Below For Updates