New Dimming Sheet Lets in More Sunlight in Winter, Less in Summer

May 17, 2013
Masaru Yoshida, Nikkei Monozukuri
The basic principle of the dimming sheet
The basic principle of the dimming sheet
[Click to enlarge image]
Light transmission properties
Light transmission properties
[Click to enlarge image]

Japan's National Institute of Advanced Industrial Science and Technology (AIST) and Sumitomo Chemical Co Ltd developed a "power-saving" sheet that blocks sunlight in summer and lets it through in winter.

The sheet can be attached to a glass window, etc. It was developed by exploiting the fact that the incidence angle of sunlight in summer is different from that in winter. It does not change the view through a glass window.

Because it is possible to adjust the amount of light coming inside just by attaching the sheet to a glass window, Sumitomo Chemical expects that it will reduce the amount of power consumed by an air conditioner, heater, etc.

The sheet is made by fitting together two transparent sheets. In general, lights coming into the transparent sheet at an angle greater than a certain degree are totally reflected when they are coming out of the sheet. If the front and back sides of the sheet are not parallel to each other, the total reflection occurs with a smaller angle, making it possible, for example, to block sunlight during daylight hours in summer. On the other hand, sunlight in winter passes through the sheet because its incidence angle is small.

However, when only one transparent sheet whose front and back sides are not parallel to each other is attached to a window, the view through the window is uplifted due to refraction. Therefore, AIST and Sumitomo Chemical fitted together two sheets to cancel out the refraction and realize a normal view.

AIST considered that glass capable of adjusting the amount of incoming sunlight depending on its incidence angle can be realized by using the total reflection phenomenon on the surface of a transparent material. And it developed a ray-tracing program for analyzing the reflection and transmission of sunlight.

As a result, AIST found a structure that blocks direct solar radiation in summer as much as possible while realizing a normal view. And Sumitomo Chemical prototyped a dimming sheet by using its processing technologies.

Sumitomo Chemical will make improvements to the manufacturing method of the sheet in the aim of realizing a better light blocking effect. It intends to develop a better method to attach the sheet to a glass window, planning to commercialize the sheet in two or three years. The company will exhibit the sheet at the 2013 Automotive Engineering Exposition, which will take place from May 22 to 24, 2013, in Yokohama City, Japan.