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Laminated Glass: Is Double Vision a Myth?

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Hi willimusk,

Last question first...laminated glass will stop over 99% of UV rays from entering your home, but laminated glass has about the same energy efficiency numbers as a lite of monolithic glass of the same overall thickness. So the answer to that question would be no.

Placing a LowE coating between the laminated lites does help energy performance numbers, especially SHG, but it isn't quite as good as LowE within an IGU (Insulating Glass Unit). Not all laminated glass manufacturers will place a LowE coating inside their laminated makeup, and of those that do, some have warranty considerations so watch for that.

Any time you are looking through multiple layers of glass you have a chance of a certain amount of distortion. When looking at a window, be it single pane or multipane, you are looking at it in two ways - transmittance - meaning you are looking through the glass and - reflectance - meaning that you are looking at the glass. The various codes and standards affecting window and glass performance do take both of those considerations into, well, consideration.

Will you see double when looking through a dual pane window at the city lights? Maybe...

Generally speaking, you are much more likely to see dual images caused by the dual panes of glass in reflection rather than in transmission. You are much more likely to see a room light on a dark night reflected back to you as a double image (especially at an acute angle) than you are to see the city lights as a double image while looking through the window.

A thought experiment: Imagine that every person who has a dual pane window saw double when looking through their window...imagine the public perception and outcry if that were true.

As a rule, you should not see double when looking at the city lights when looking through a dual pane window. There are occasions when the lights could appear a bit "out of focus" depending on a few variables and you could see a slight ghost image in the right circumstances, but as a rule you should not generally notice a difference between a dual pane and single pane window.

You wouldn't happen to be in South Florida would you? I have heard versions of that question from that part of the country a few times before. Some folks down there seem to think that the introduction of dual pane windows is on a par with floridating the water - communist plot instituted by the devil himself.

Actually, the very worst transmittance and reflectance images I have ever seen were through laminated tempered glass. All tempered glass is distorted to some degree, even if you might not really notice it, but when laminating two lites together you tend to have some significant non-parallel surfaces on the two outer faces of the unit which can cause really interesting distortion patterns. Several laminators will not warranty a tempered laminate for distortion issues, telling customers that if they want tempered laminate, they have to live with the distortion.

Source Post: "Double vision" of dual pane glass?
Posted: Sat Jun 04, 2005 10:38 am Post subject: double vision