Transparent Wood Provides Lighting and Insulation
John Simpson | September 09, 2016Engineers at the A. James Clark School of Engineering at the University of Maryland say they have demonstrated that windows made of transparent wood could provide more even and consistent natural lighting and better energy efficiency than those made from glass.
In May 2016, researchers headed by Liangbing Hu, of the university's Department of Materials Science and Engineering, removed the molecule in wood—lignin—that makes it rigid and dark in color. They left behind the colorless cellulose cell structures, filled them with epoxy and came up with a version of wood that is mostly see-through. Now Hu's research team is reporting that the material provides better thermal insulation and lets in nearly as much light as glass, while eliminating glare and providing uniform and consistent indoor illumination.
"We also learned that the channels in the wood transmit light with wavelengths around the range of the wavelengths of visible light, but that it blocks the wavelengths that carry mostly heat,” says postdoctoral researcher Tian Li.
The channels in the wood transmit light with wavelengths around the range of visible light, but block the wavelengths that carry mostly heat. Image credit: A. James Clark School of Engineering.The team’s findings were derived in part from tests on a tiny model house with a transparent wood panel in the ceiling that the team built. The tests showed that the light was more evenly distributed around a space with a transparent wood roof than a glass roof.
The channels in the wood direct visible light straight through the material, but the cell structure that remains bounces the light around, a property called haze. This means the light does not shine directly into one's eyes, making it more comfortable to look at.
Transparent wood still has all the cell structures that comprised the original piece of wood. But the wood is cut against the grain so that the channels that drew water and nutrients up from the roots lie along the shortest dimension of the window. The transparent material uses these natural channels to guide the sunlight through the wood.
As the sun passes over a house with glass windows, the angle at which light shines through the glass changes as the sun moves. With windows or panels made of transparent wood instead of glass, as the sun moves across the sky, the channels in the wood direct the sunlight in the same way every time.
"This means your cat would not have to get up out of its nice patch of sunlight every few minutes and move over," Li says. "The sunlight would stay in the same place. Also, the room would be more equally lighted at all times."