Now, wood windows that keep homes cooler than glass

Scientists have developed new windows made of transparent wood that could provide more even and consistent natural lighting and keep houses cooler than glass.
Led by Liangbing Hu of University of Maryland (UMD) in the US, researchers showed that their transparent wood provides better thermal insulation and lets in nearly as much light as glass, while eliminating glare and providing uniform and consistent indoor lighting.
The transparent wood lets through just a little bit less light than glass, but a lot less heat, researchers said.
"It is very transparent, but still allows for a little bit of privacy because it is not completely see-through," said Tian Li from UMD.

"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," said Li.
The team's findings were derived, in part, from tests on 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 still remains bounces the light around just a little bit, a property called haze.

This means the light does not shine directly into your eyes, making it more comfortable to look at.
Transparent wood still has all the cell structures that comprised the original piece of wood. 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 new transparent wood uses theses natural channels in wood 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.
Working with transparent wood is similar to working with natural wood, the researchers said. However, their transparent wood is waterproof due to its polymer component.
It also is much less breakable than glass because the cell structure inside resists shattering.
The process for making transparent wood starts with bleaching from the wood all of the lignin, which is a component in the wood that makes it both brown and strong.

The wood is then soaked in epoxy, which adds strength back in and also makes the wood clearer. The team has used tiny squares of linden wood about 2cm x 2cm, but the wood can be any size, the researchers said.
The research was published in the journal Advanced Energy Materials.