Expert: Daniel Humphrey - 5/15/2010

Question
We are building a sunroom addition with a large fixed window. The window is made of tempered glass and sealed with argon gas. There is an unusual "plasma" effect in the center of the window. If you press on it, it creates a similar effect to pressing on an lcd screen. Is the argon leaking or the seal broken. It is very large and already installed. It is only noticeable in certain angles. Should I have it replaced? Thanks in advance. Lauren

Answer
Dear Lauren,

The effect you're seeing is the result of light refracting through the panes of glass and the argon. Nothing is wrong with the window!

When you press on the glass, you deform the glass and narrow the gap at that point, and since the light is passing through the glass and argon at angles, the result is that some of the light where you're pressing will come closer to neighboring light rays and become brighter in places. In other places, the rays are more spread out, causing a darker effect. Such an effect is more prominent when the light is polarized.

Daniel