Archive for the 'Technical' Category

On-Angle Performance Measurements -My Angle

Well I guess it’s about time for me to address the whole “on-angle” Total Solar Energy Rejection measurement. As many of you are aware it is a measurement that is currently marketed by 3M to show the performance of their Prestige Window Film line. The whole premise is that the window film industry has always tested and derived the Total Solar Energy specification at 90° perpendicular to the glass. 3M reasons that the sun does not reside at 90° throughout the day, especially at the hottest part of the day, thus the need to create a film that in their mind performs better “on-angle.” So the need for an “on-angle” measurement arises and subsequently the specification finds its way into their marketing literature.

Despite the fact that the window film industry has never promoted such a measurement and the NFRC does not post angular performance data on the product certification labels, the general public is left to assume that this is a common measurement that sets one product apart from all others. The assumption gets propagated further when window film dealers add inaccurate statements and insert fiction into what is fact. For instance one dealer writes a rebuttal on their website in response to the statement:

3M’s total solar energy on angle spec is not supported by the National Fenestration Rating Counsel

Dealer’s Response: This is true but this is new technology. No other manufacturer (glass or window film) can rate their product this way. The two hundred layers in the new 3M Prestige window films with nano technology make this new on angle specification possible. All window film manufacturers measure the total solar energy rejected at a 90 degree angle to the glass.

Let us separate fact from fiction here…

Fact: The NFRC does not support the Total Solar Energy Rejection On-Angle specification. All manufactures measure the total solar energy rejected at a 90 degree angle to the glass.

Fiction: The statement that this is new technology and that no other manufacturer (glass or window film) can rate their product this way. Also the statement that it is 3M’s multi-layer nano-technology that make this new angular specification possible.

The reality is that any manufacture can easily report their performance ratings this way, if they wanted too. This specification is not made possible by the unique construction of Prestige Window Film’s multi-layer technology nor is the on-angle measurement a new measurement. Lawrence Berkley Laboratories has had software available for many years that gives angular performance data of window coatings and window films on almost any glass type available. This software and the measurements that result from it are recognized by the Department of Energy (DOE). 3M did not invent this measurement and neither did any other window film manufacturer for that matter. So let’s use this LBNL software and run our own test comparing “on-angle” performance data of a few films. This particular test was run on clear single pane glass .120 inch in thickness with some 70% vlt films that have their specifications listed.

Sun’s Angle

SHGC @ 0°

SHGC @ 30°

SHGC @ 60°

SHGC @ 80°

SHGC @ 90°

Prestige 70






Vista VS 70






V-Kool 70






What I’m seeing here is that there is on-angle data available for all 3 brands not just Prestige. The SHGC or Solar Heat Gain Coefficient is the opposite of the Total Solar Energy Rejection measurement. The lower the number, the better the overall performance. So ignore the fact that Prestige 70 gets outperformed on every measurement by the other two films, but rather, focus on the pattern. As the sun’s angle increases, the performance of each film increases as well. So much so that when the sun is directly above the window all of these films perform extremely well; they reject all of the sun’s energy! By the way… clear glass has a 0.00 SHGC at 90° too. Why? Obviously as the sun orientates to a higher angle above the window less energy transmits through the glass.

So this whole idea of a company’s technology making a new measurement possible or window film being designed to be unsurpassed by any other window films in on-angle performance is unfounded and inaccurate. Let’s give the consumer some dignity as well as some accurate and relevant data that will not fool them into believing that one product is something that it is not. Window Film Manufacturers can do this by adopting standardized performance measurements and using well respected third party agencies like the NFRC to verify these measurements. Window Film Dealers can and should educate themselves so that they do not propagate inaccurate and false information to the consumer for if they continue to do so, it will only serve discredit a product that is so badly needed in a time where energy conservation is vital.


Is it Accurate?

Accuracy counts… in some things.

-“He missed by a mile!

-“We were close…”

-“Looks good to me…

These expressions are one thing when stated by your sports caster or weatherman but quite another if you heard your accountant or surgeon make such statements. Accuracy is important, even vital in some instances.

The window film industry has suffered from inaccuracy, inflated paybacks, unfounded statistics, and misapplied specifications among many other things. For instance, how many times has someone misapplied single pane 1/8th inch glass specifications saying that a 15%vlt window film will block 80% of the total solar energy when the window that is being considered is dual pane? If you did then you certainly missed this one by a mile for the total solar energy rejected on insulated clear glass is closer to 71% not 80%! “Well, we were close” you may say… Hardly! What if this was a 40,000 sq foot project? The results would be different, one would be accurate and the other would be inaccurate.

This scenario can create a chain reaction of misinformation such as an inflated payback or ROI (return on investment). Statistical data becomes inaccurate when we do not take the time to generate factual data. We then have a problem because once someone discovers that we have taken liberties with specifications it erodes our credibility as a whole. It is much more beneficial to not only bring accurate data to the table so to say, but to also be able to verify that the data is accurate and explain why that is so.

For years now the window film industry has measured most of their published specifications on 1/8″ clear single pane glass. We blogged why this was the common practice and the reasoning and benefit behind it. There was always a need for a standardized specification and standardized testing that could be verified by a neutral 3rd party to be both accurate and at the same time recognized by agencies such as the Department of Energy (DOE). This was a crucial step in leaving old practices behind and moving a head in the promotion of accuracy. It was also vital so that single-region measurements would not be mismarketed to the general public and misinterpreted as total solar performance data.

A landmark occasion has arrived for the window film industry. There is a neutral 3rd party organization to certify window film performance specifications not just on single pane glass but on dual pane glass as well. The National Fenestration Ratings Council (NFRC) is a non-profit organization that administers the only uniform, independent rating and labeling system for the energy performance of windows, doors, skylights, attachment, and applied window film products. Currently, there are two window film manufacturers with certified products listed in the NFRC Applied Films Directory. This accurate data can be used to not only compare the total performance of one film to the next, but it can also be used to calculate the glass’ affect on building performance and the return on investing in window film.

We have come a long way from presenting our customers with a specification card that in most instances does not apply to their glass situation and yields an inaccurate result. NFRC Certified Films are now recognized by the DOE as an energy saving device and in time, will qualify to be rated as Energy Star products. Consumers can rest assured that they are being given the most accurate and relevant data to date so the they can be confident in their buying decision.


IR Rejection Part2 –The Slight of Bandwidth

I might catch a bunch of grief over this blog but I feel it is something that needs to be addressed. We have long used BTU Meters in our industry as an easy way to illustrate window film’s performance to a consumer. An Infrared heat lamp is placed in front of a BTU meter and a measurement is then noted. Next a piece of window film is placed between the meter and the lamp and WOW! The meter almost bottoms out to zero. What just happened?

Before I address that question let me just say that this type of demonstration does have its place in a sales presentation. The heat lamp demonstration is a way to allow a consumer to “feel” the difference between a filmed and unfilmed piece of glass. I agree that this is a good way to demonstrate that window film works and that it is a viable way to increase the performance of glass. Here is the part that I take issue with; Improperly trained sales persons will use this IR lamp demonstration and compare the BTU measurement between different window films. The way that they present the results leads a consumer to conclude that one film’s superior BTU reading means that it overall outperforms the other films that it is being compared too. Note the following demonstration found on You Tube: [Update See Why This Video Is Unavailable] [Another Example Can Be Found Here]

In my opinion this is a deceptive practice. What you are seeing is a lamp that throws out over 90% of it’s energy as infra red radiation and a meter that is designed to measure the amount of infrared that it is being bombarded with. There is no way to account for the energy in the Visible Light Spectrum which makes up a sizable portion of the total solar energy because Infrared Light Bulbs are not designed to produce visible light. Remember too, in a previous blog we established that IR rejection does not translate to overall film performance. Nonetheless, let’s break this demonstration down by asking ourselves some questions.

What wavelength does this meter sample at? Well a little research shows that it is between 900-1050nm. Is this the entire Solar Spectrum that is being sampled? No, the solar spectrum starts at around 300nm and extends past 2500nm.* It becomes clear that BTU meters like the one in the demonstration are not capable of measuring total solar performance past 1050nm.

What wavelengths of the IR spectrum is the film rejecting energy? Some films are designed to reject IR at 900-1000nm. You can find these references as footnotes added to IR rejection specifications. If you refer back to the solar spectrum chart in our previous blog you will see that this particular wavelength range is one of the lowest intensity areas in the IR spectrum. That just so happens to be where beam splitters sample IR rejection (950nm) and it is also part of the “sweet spot” that some BTU meters sample at. So if a particular film performs best at that specific wavelength then it is naturally going to produce a better reading on a BTU meter than other films, but this does not necessarily mean that its overall energy rejection will be better. Why? As we have established, Total Solar Energy Rejection is an entirely different, and more accurate, measurement that IR rejection. Total Solar Energy Rejection (TSER) and the Solar Heat Gain Coefficient (SHGC) are total performance measurements that take in the entire solar spectrum rather than select wavelengths. Due to the publishing of single region measurements that can be marketed to resemble total performance, such as IR rejection, the International Window Film Association went so far as to publish a clarification on the difference between IR rejection and Solar Heat Gain Coefficient measurements. SHGC measurements can be used to accurately compare the total performance of one window film to another whereas single region measurements cannot.

Therefore to imply that BTU readings are an accurate test to determine overall performance from one film to the next has no basis according to the facts. It is a deceptive sales presentation to say the least and in my opinion it should cease to be used in this manner. Third party performance testing by a reputable organization such as the NFRC is a much more accurate and reliable way to gather and publish data so that you can compare the performance of one window film to the next. Ask your sales professional to provide you with NFRC test results rather than hyped up marketing demonstrations designed to capitalize on a consumers lack of understanding.


*ASHRAE 2005 Handbook Fundamentals– 31.14

Infrared Rejection

Window Films are capable of rejecting Infrared (IR) but oftentimes this can be mistaken for Total Solar Energy Rejection. Improperly educated window film dealers, crafty marketing on the part of manufactures, and a lack of standardized testing can propagate misinformation leading a consumer to conclude that a window film will reject up to 98% of the heat! This just isn’t true at all. Let’s take a few paragraphs and learn what infrared is, why it is listed on some specification cards, and how IR rejection should be interpreted.

Infrared –What is it?

Energy created by the sun travels to earth in different wavelengths. These wavelengths make up what is known as the “Electro Magnetic Spectrum” or EM spectrum for our acronym dependent crowd out there. The diagram above illustrates how differing wavelengths affect us in different ways. When it comes to our windows and energy control we are affected primarily by what is known as the “Solar Spectrum” which is a band of frequencies made up of Ultra Violet, Visible, and Infrared wavelengths. These three areas are responsible for what we feel as heat and the total solar energy that results from solar spectrum can be regulated by window film.

The chart above shows that energy is distributed across the solar spectrum in 3 distinct bands. Infrared frequencies extend from 780 to 2500nm and beyond. 53% of the sun’s energy comes to us in this band whereas 44% of the sun’s energy is in the form of visible light and 3% in the form of UV radiation. (Note: See Updated Understanding of Energy Distribution Across the Solar Spectrum.) As you can see infrared radiation is a band of electromagnetic wavelengths that account for 53% of the sun’s energy. Clearly, this band cannot be interpreted as Total Solar Energy (Heat) nor can it be used as a total performance specification to differentiate one window film’s ability to regulate the total amount of energy that enters through glass over another film. So why do some manufacturers publish this specification in their literature?

Why List IR Rejection Percentages?

We mentioned earlier how window film can be designed to regulate these three bands of the Solar Spectrum. Certain materials that have spectrally selective properties can be incorporated into film substrates. There is one family of films that primarily focuses on IR rejection while allowing more of the visible light to transmit through the film. These films are sometimes referred to as Spectrally Select Window Films because they regulate specific wavelengths of the EM spectrum. With the advent of Spectrally Select Films eventually came the justification to list the performance of the primary regulated band in the solar spectrum namely, the infrared rejection. As a result, you will find some manufacturers listing their product’s IR rejection in varying percentages.

How Should IR be Interpreted?

Even if these specifications came about with the most noble of intentions, the reality is that IR rejection specifications can certainly be capitalized on with a little crafty marketing or simply from a salesperson that lacks the proper training and education. If we simply keep in mind that any given IR rejection percentage is simply telling you that the film is rejecting xx% of the IR band which makes up 53% of the total solar energy then it becomes easy to interpret performance in the context it belongs in.
One note of caution must be mentioned. Marketing departments can report IR rejection any way that they want because there has never been an industry standard for reporting IR rejection. One strategy for reporting extraordinarily high IR rejection numbers is to sample specific wavelengths in the IR band and report rejection. For example, a film’s specification card may say that it rejects 97% of the IR. Wow that is amazing! Or so it looks that way, however when you do some further investigation you find that they are only reporting this IR rejection percentage between 900-1000nm. Is that the entire near IR band which extends from at least 780-2500nm? Hardly! So is this film really rejecting 97% of the IR? No, it is actually closer to 86% when you average it out over 780-2500nm. We will go into more detail in future articles but suffice it to say, buyer beware. Standardized performance measurements such as the Solar Heat Gain Coefficient (SHGC) which is recognized by the NFRC the only non-profit independent rating agency for window and applied film performance is a much more accurate total performance specification that can be relied upon to compare one film’s performance to another film. Fortunately, there are many well-trained professionals in the window film industry that can help you to find the right product for your needs but it certainly does not hurt to do a little research and educate yourself along the way.

Total Solar Energy –What You Need to Understand

Ok, so what is this term that we hear about called “Total Solar Energy Rejected?” Often times we see some untrained window film dealers implying that this is temperature reduction percentage. Well, not really… while the measurement does translate indirectly to temperature reduction it should never be confused with it. Why is this so?

Heat and Temperature –What is the Difference?

When we measure temperature we are measuring the intensity of molecular motion. If you were to measure the temperature of the flame created by a lighter versus the flames of a forest fire they would be similar, however, the forest fire would generate much more heat than the lighter. Heat is a unit of energy. So even though the temperature of the flames are the same the far greater volume of mass of a forest burning will result in much more energy (heat) being produced.

The energy that makes up the solar spectrum is divided into three areas, Ultraviolet Radiation, Visible Light, and Infrared. Their intensities vary depending on their wavelength size and each one accounts for varying percentages of heat as indicated in the following diagram. (Note: See Updated Understanding of Energy Distribution.)

Total Solar Energy Pie Chart

As you can see 53% of the sun’s energy comes to us in the Infrared Spectrum, 44% from the Visible Light Spectrum, and 3% from the Ultra Violet Spectrum. All of these three areas make up what is known as the Solar Spectrum and their combined energy is what we are referring too when we use the term “Total Solar Energy.” Window Films act as a filter reducing varying percentages of each part of the Solar Spectrum. Darker films will filter out more visible light resulting in energy reduction whereas lighter films have to filter out more infrared in order to reject large amounts of energy. Films can be designed to work on either one part of the Solar Spectrum or all three. Clearly then when we read the specification called “Total Solar Energy Rejection”, we can now see that it is not referring to temperature reduction percentage, but rather, it is the percentage of incident solar energy rejected. The Total Solar Energy (TSER) specification along with another specification that is commonly used in the glass industry called the “Solar Heat Gain Coefficient” (SHGC) are two excellent ways for a consumer to compare the performance of one window film to another.

Window films alone cannot lower the temperature of a room but they can reduce the rate that energy enters a room which helps reduce the load placed air conditioning systems. The greater the glass area, the greater the impact window film can have on heat transfer into or out of a room. This makes window films an essential component to creating a more energy efficient building or home.