Having an old-timers moment...

… or maybe too early and not a second cup of coffee!

If anyone has experience in low E. glass with or without thermal imaging experience, I can use some help.

I inadvertently came across a situation inspecting a high-rise condominium complex. I was not inspecting the window glass I came across two conditions that I am trying to describe and am having a brain cramp this morning.

First window I found was from the interior. I had heat on, exterior temperature about 67°F (indoor temperature about the same but in a rising transition). The window was not solar load it and faced the East. It was high noon so the window is in transition.

The center window recorded an apparent temperature rise of 4°F.

The actual visual appearance of the center window was lighter in color than the other windows. There was a significant difference (increase) of visual light transmittance of the center window versus the other windows when viewing the aluminum frame between the window glass.

You can see a more definitive reflection of the interior wall and studs and floor in the center window then the other windows. This window appears much greater reflectivity (even though it is lighter in color) than the other windows.

This is an exterior scan of the same window. The apparent temperature of the window is 2.5°F cooler than the others. The reflections in the lower half of all Windows is a high concrete wall around the patio.

None of the other windows in his high-rise building displayed these anomalies.

A second window was observed at the same time but was solar loaded (about to go into the shade). This is an interior shot and the window has an apparent temperature 8° cooler than the other windows.

This window was also much lighter in color than the other windows.

These are two different scenarios because of the solar loading difference and getting confused and would appreciate any observations/interpretations you see.

My problem is about incident radiation versus total radiation. Being glass, the emitted radiation is a very small part of the total radiation. Confusing the total radiation with emitted radiation leads to considerable error. I leave temperature measurements off of these scans because of this. What the camera is recording is nowhere close to the actual temperature being emitted.

As I was not actually evaluating these windows, I did not collect the data required to determine the glass emissivity, U-values etc. I did not determine the actual temperature of these windows. Solar loading conditions changed within minutes and these conditions evaporated quickly!

So what I’m asking is qualitative opinions on what appears to be happening to cause these windows to “appear” to be different temperatures.

All of the images look relatively normal to me. I’m not sure what “qualititive” type of analysis you are looking for. It appears that you are seeing heat reflections in the windows. One reason you would see different patterns in the panes of glass would be viewing angle.

Did you change your viewing angle? And if so, did it make a difference in the images.


Not being an infrared person, I can only pose a question.

Low E film is applied to an inner surface of one of the panes. Depending on the location of the window, the film is applied to either reflect or absorb solar radiation. So my question is, could this particular window be installed “backwards” or in the opposite direction of the surrounding windows?

Hello Kevin,

I was on the phone with Jim Sefferin and he told me of your reply. Thank you!

By qualitative I mean that I did not collect quantitative data necessary to make this assessment due to numerous situations. I did not put any reference temperatures in the scans intentionally as I do not want them to distract. I am asking that you take a visual assessment of what is quantitatively in these scans (for what they are worth) and formulate a hypothesis of your observations as to what may be causing this anomaly. I realize there is insufficient information and data at this point to make a definitive call.

The reflections in the window; I intentionally used these scans because the reflections detect differences in reflectivity (between the interior and exterior views). I did take other views where only the clear sky was reflecting in the windows. The same condition was evident without the reflections.

If you notice in the first scan the studs are very reflective compared to the other two windows, but from the exterior the reflection of the wall was less in the center window than the other two windows. This leads to some of the confusion and is why I used these perspectives.

So far, the derived consensus is that the windows are likely to have been manufactured differently and share different properties to one another affecting numerous thermal effects of the glass.

The end result of this investigation, (if determined) will be documented and disseminated to those responders of this inquiry for your future reference.

Yes, this has been considered and discussed behind-the-scenes.

The etched labeling on the glass is facing the same direction, however the location of the labeling is at the top of some and the bottom of others. Orientation of a polarized film could possibly cause this effect.

Attempts to determine manufacturer’s specifications and construction will be made to ascertain if polarization or direction of installation may affect performance.

A consideration that Jim Sefferin and I discussed about the Low-E film is that in this case, the film is located within the window construction (some aftermarket products are applied on the exterior). Therefore it is hypothetically “invisible” from the thermal camera, though it may affect the actual temperature of the window system that is being detected by the camera through transmittance and absorption of thermal energy.

Attached a some tape to the window glass and measure the temperature
of the tape, and bypass the reflection issues. Move on to the next item.
Keep it simple.

Yes, there was anticipation of this response…

There are a few more circumstances behind the scenes. The client is a lawyer. The client works for high ranking executives of Cummings diesel (worldwide). The client has extreme “clout” not only Nashville, but throughout the Cummings world! We all may be able to receive recognition about this technology that could span the globe due to one client!

I’m not trying to solve a simple solution just to answer a clients question or to make myself appear significant to this client. I think this is a significant question and that the results of this question and investigation will help future assessment by qualified infrared thermographers.

We are discussing a situation that is probably the most difficult infrared thermal imaging diagnostic in existence.

If I put a piece of electrical tape on the window and take a thermal scan of the tape, please advise me exactly what this data collection will contribute to the diagnostics of this window and situation?

Does the temperature of the glass supersede all possible effects of transmittance and reflectivity? It seems to me that you were promoting a product that blocked the effects of solar radiation through glass. If the glass component does not adequately reflect electromagnetic radiation or prevent transmittance of this radiation where it is absorbed and re-emitted when it strikes the interior components of the residents, could this not affect the environmental conditions within the residence (regardless of surface temperature of the glass)?

It’s almost impossible to formulate a “hypothesis” without actually being there for the scan and knowing exactly what it is you are trying to figure out. There are a ton of variables in this scenario.


Thank you…my head was starting to hurt before I decided the same to relieve it. :smiley:

Good luck, David and keep us posted.

What floor of the complex are these windows? You said high rise, just not how high that would be.

The middle window, first image, has to be different if it is the only window in the whole joint showing this effect (obviously). I would ask the property owner if it was ever replaced. It is also completly possible this window got switched somehow during original construction, or somehow was broken before installation and they had to order a new one. All kinds of reasons could come up as to why this window is not original, or at least part of the original batch that was installed.

I would think there are many other items that could make it “different”…ranging from film, to backwards installation, pane flipped frame, so on and so forth.

Would love to know what you and Seffrin come up with this one, and what the end result comes in at.


Any chance the 2 windows in question have been replaced with a triple pane insert?

Beyond potential polarization issues as discussed… could the panes possibly be closer together in the center window than the other two… similar to JJ’s post… my inclination is that the window had been replaced… or possibly a thermal seal “repaired”

Interesting post Dave.

David, are the glazing/spacer bar’s all the same or is this window different?

Like everyone else there is limited info. to go on.

Thanks for the replies!

I know we are lacking information here but this is not a test for a definitive answer, rather your first impression of what were looking at. I tried to point out a few issues that seem to be contradictory or puzzling to me.

If anyone has any experience about Windows such as is window film polarized, how different orientation of the film may affect, location of the film etc.? That’s what information I’m looking for.

What I’m trying to achieve is when we see this anomaly in the field, we have a better idea of what’s going on. Is this really a significant defect or is it just something we see that is cosmetic (different colored tint).

I figured John would come up with something qualitative because of his practice of not using quantitative analysis in home inspection. However he posted quantitative testing procedures rather than performing a visual hypothesis which is what I’m looking for.

If anybody has any ideas, I will go out there and try them out and attempt to verify if they are applicable.

Kevin, I’m just asking for a SWAG. Just some help with perspective. If you were to come across this, what would be your thoughts?

Jason, this was on the fifth floor of a 10 story building. We are asking property owners about past history and installation information. Do you know if backward installation is critical? The etched label on the window was oriented front to back the same as the others but not from top to bottom.

Jeffrey and Peter, they are all the same window design, even the etched labeling on the window is the same. However, they are obviously different in some way!

Bill, visually the distance between window glass appeared the same. However we know that a very small amount of difference in spacing can cause that bull’s-eye pattern.

Concerning the type of Low-E film, this film is located on the interior of the Windows and thermal imaging can not determine its temperature directly because it cannot measure through the glass. Transmissivity through glass is there but is very minimal and not sufficient enough for these large temperature differences. Conduction will change with material used in the glass and the gases between the windows. Different gases will cause different conductivity which will eventually affect the actual surface temperature that the IR camera is measuring. The temperature gradient across the glass panels is very evenly distributed from edge to edge. It is apparent that there actually is a temperature difference between the glass (versus incident radiation effects). There are obvious differences in specular reflection between windows.

We will continue to work on this and keep you all posted.
This anomaly has sparked a lot of interest across the board.
If we can derive a definitive answer in this case we will document the case study.


How did you determine the glass is Low-e? Did you put a piece of paper next to the panes to look at reflection?

This site may help you on your thirst for knowledge or quest for the answers :slight_smile:


Good luck…



Thanks Kevin!

Your welcome :slight_smile:

You might want to also take a look at RESFIN. I’ve used it twice in the past to help clients with selecting window replacements when I was modeling their home for Home Energy Performance Surveys. It’s a very cool “free” software.


But… now that I read that again, IR doesn’t pass through ANY glass!?:shock:

Long wave doesn’t (or very little)… short wave does. Or at least that’s what I was taught. Hence how/why a greenhouse works.

I wonder if the absence/presence of argon gas (or dissimilar gases) could also create what you saw. (Not sure…) What you recorded resembles the difference between single pane and double pane side by side comparisons looking through a long wave imager. You’ve certainly got my interest peaked Dave. :slight_smile: I believe this will certainly take more investigation than an IR imager can provide to figure out.

This is going to open a new window in IR… L.O.L. Looks like one should put together a hand book on windows and how each window or type of covering views under IR.

With all these new windows and NEW window products on the market one could make a mistake in there findings.