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August 29th, 2022 by Nathan Hobbs

Terms of the Trade

By Manny Hondroulis

During training, a lot of time is spent on understanding the various performance characteristics of window film, such as:
• Visible light transmission (VLT);
• Glare reduction;
• UV blocked;
• Solar heat gain coefficient (SHGC);
• Total solar energy rejected (TSER);
• U-value; and
• Heat loss reduction

An end-user chooses a window film based on its performance and aesthetics, so it is imperative that anyone in an industry sales role understands these basic performance characteristics.

It surprises me how many industry veterans don’t know these terms. Product and technical training, or lack thereof, is one of our biggest challenges. Becoming a window tinter or dealer has low barriers to entry. Many enter without receiving the proper sales, technical or installation training. They learn as they go. While anyone in a small business can appreciate the can-do spirit of “learning on the fly,” a lack of product understanding can do the customer, dealer and industry a disservice.

While many of the terms above are technical in nature, they are by no means impossible to understand. Take, for instance, Glare Reduction. How many in the industry know the mathematical equation for it? Simply stated, how many know that Glare Reduction is the percent change of Visible Light Transmission from before film to after film? This means that Glare Reduction is only a function of Visible Light Transmission.

The darker the film, the more glare that will be reduced. Glare reduction has nothing to do with a film’s reflectivity (although there is usually a correlation between VLT and reflectivity in that films with lower VLTs tend to be reflective), composition, TSER or anything else except for visible light transmission. So, a 35% film with no reflectivity will reduce more glare than a 70% film with high reflectivity.

Energy Education

Another popular term is Total Solar Energy Rejected, or TSER for short. TSER happens to be the opposite of Solar Heat Gain Coefficient (SHGC). (In fact, when you add the TSER and SHGC of a particular film, the sum is one or 100%.) Think of TSER as to what happens on the outside of the window and SHGC on the inside.

The sun’s incident energy, ultraviolet, infrared and visible light, hits a window. The energy that is reflected by the window plus the energy that is absorbed by the window and reradiated outward equals the TSER. The energy that is transmitted through the window plus the energy that is absorbed by the window and reradiated inward equals Solar Heat Gain Coefficient. That’s why TSER plus SHGC equals one or 100%.

You have probably seen the term Infrared Heat Rejection followed by a high number such as 98%. Sounds impressive, doesn’t it? It makes you think that a film will reject 98% of the sun’s heat from passing through a window, thereby eliminating the need for air conditioning. Well, it’s simply not true. A term like Infrared Heat Rejection focuses exclusively on infrared without
regard to UV or visible light. In addition, the measurement, in this case 98%, is usually taken on only a small portion of the IR spectrum. While Infrared Heat Rejection is a technical term (some might consider it more of a marketing term) and has a place, it needs to be explained adequately by the dealer to the end-user.

TSER (or SHGC) is the most insightful performance characteristic to the overall effectiveness of a sun control film as it considers UV, Visible Light, and IR altogether.

U-Value, which is the inverse of R-Value, is equally important as it determines a film’s overall effectiveness in retaining artificial heat during the colder months. The lower a film’s U-Value, the less heat is lost through the glass to the outside. It is U-Value that serves as the basis for calculating Heat Loss Reduction. Heat Loss Reduction is the percent change of U-Value from before film to after film.

Manny Hondroulis is the vice president of Energy Distribution Products in Baltimore.

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