Laboratory test of thermochromic and electrochromic glass optical & thermal properties

The optical properties of a thermochromic glass change with the glass temperature. For example, the glass is tinted with increased glass temperature.

The optical properties of an electrochromic glass change with the electrical control. For example, the glass is tinted with an electrical voltage applied.

The optical and thermal properties (e.g. visible light transmittance or VLT, solar heat gain coefficient or SHGC, and shading coefficient) of a thermochromic glass or an electrochromic glass can be tested as an ordinary glass, as described in this article, except that the optical states need to be properly controlled in the lab.

Thermochromic glass optical state control

For thermochromic glasses, the glass temperature needs to be controlled. Shown below is the setup available at OTM for thermochromic glass temperature control.

A rubber pad heater with a 1-inch circular opening at the center (the amber color part) is attached to the thermochromic glass surface. The power output to the heater is regulated by a temperature controller, based on a thermocouple attached to the glass surface.

With this setup, we’ve successfully measured one thermochromic glass in the temperature range from room temperature to 65 °C, with temperature stability better than 1 °C and temperature accuracy better than 2 °C.

Thermochromic glass temperature control setup

Electrochromic glass optical state control

For electrochromic glasses, an electrochromic glass controller needs to be provided by the customer. It can be a simple device with a constant DC voltage output. Shown below is the setup.

We’ve measured a few electrochromic glasses, with customer’s controller.

Electrochromic glass electrical control setup

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