Smart Liquid Lenses Let the Sunshine In
Tom Lombardo posted on November 24, 2013 |

Lighting accounts for 21% of the electricity used in the commercial sector. Offices are occupied mostly during daytime hours, and natural sunlight delivers a spectrum of light that’s most conducive to productivity and psychological well-being. It makes sense, therefore, to have as much natural lighting as possible available in offices. Unfortunately, not every office is located near a window, and even where windows are present, the apparent movement of the sun throughout the day means that a room may only have optimal sunlight for a few hours each day. The rest of the day is lit by fluorescent lights, which use electricity and produce a spectrum of light that’s inferior to natural daylight.

Light tubes such as the SolaTube offer a low-tech way to bring daylight into windowless rooms, but they’re mainly designed for residential locations and they produce a diffuse light that spreads around a room. If you need a bright light on a particular area, you’ll probably have to turn on an electric light.

Imagine an array of tiny lenses that can redirect sunlight towards any interior room of a building. Even better, the lenses can focus light onto any small location for task lighting. Thanks to the burgeoning field of electrofluidics and a pair of innovative researchers at the University of Cincinnati,  we may see this technology in the near future.

Anton Harfmann, Associate Dean and Professor of Architecture and Interior Design, and Jason Heikenfeld, Professor of Electrical Engineering, have collaborated on a project that could bring natural daylight to interior rooms. Even better, their SmartLight uses no net electricity and offers the possibility of using excess light to generate electricity. And it all revolves around a drop of electrically charged fluid, similar to a pixel in an LCD TV.

The Big Picture

As shown above, light enters the building through exterior windows that contain arrays of electrofluidic (EF) cells. The EF array can then direct light up to the ceiling for general room lighting, and can also focus a more intense light to specially-designed fixtures to produce concentrated task lighting (top frame of image below). All rooms would include transom windows with EF cells embedded in them, allowing unused light to pass to interior rooms. Light that’s not used by any rooms is then directed to a central location for storage. (See image below.) The user controls room lighting with a smartphone app that talks to the WiFi-enabled array.

Electrofluidic Cells

An electrofluidic (EF) cell contains a droplet of transparent fluid - just a few millimeters in size - with a negative charge. Applying a small voltage to one or more sides of the cell changes the droplet’s shape, allowing it to become a lens that can focus light in any direction. The electricity comes from tiny photovoltaic cells - so small that they only absorb about 10% of the light. Because the electrofluidic cells only need a small voltage to change their shape, the trickle of electricity from a small PV cell will do the job.

The voltage is applied intermittently. The EF cell retains its shape for a while but needs occasional refreshing, somewhat like the dynamic RAM in a computer. Dr. Harfmann told me that the cells would need refreshing every minute or two, in order to retain their shapes and to adapt to changing light conditions caused by changes in the Sun’s position in the sky. Dr. Heikenfeld is experimenting with different voltage levels and associated controls that can shape the cells and steer the light. The researchers have tested EF cells on a small prototype array of about  6 square centimeters and found the principle to work. (In fact, Dr. Heikenfeld has spent several years working on a variety of other applications for electrofluidic cells.)

Excess Light is Stored (sort of…)

As far as I know, one cannot simply accumulate photons in a bucket for later use. Until we can do that, Harfmann and Heikenfeld suggest directing excess light to a central location, concentrating it, and focusing the concentrated light onto high-efficiency photovoltaic cells. The resulting electricity can either be used on-site, sold to the grid in a net-metering agreement, or stored in batteries. The heat that results from concentrating the sunlight can be used for space heating or water heating.

The Future Looks Bright

The researchers are currently applying for grants to fund a large-scale prototype. They anticipate about 1-2 years to develop working prototype. If they can find enough investors, we could see this technology commercially available in about three years.

It looks like an ambitious project but certainly doable for new constructions, and even as a retrofit on existing buildings. A retrofit would need transom windows installed and it seems unlikely that the central storage hub would be feasible, but you would at least be able to get natural light to interior rooms. As someone whose office is on the ground floor (i.e. basement), I wouldn’t mind having a little daylight shining down on my desk. Maybe I’d have a sunnier disposition - my students would certainly appreciate that!

Images: Renderings by Timothy Zarki, courtesy of The University of Cincinnati

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