Window Film Performance Terms Explained

Quick Reference

Window film performance terms at a glance

What each rating measures, how it is expressed, and which direction is better. Always compare ratings for the same glass.

01 / Solar Energy Basics

How sunlight interacts with glass

When sunlight strikes glass, three things can happen. Some solar energy is reflected away from the glass, some is absorbed by the glass, and some is transmitted through the glass into the building.

These three values always work together. If more solar energy is reflected, less may be absorbed or transmitted. If more energy is absorbed, the glass may become warmer. If more energy is transmitted, more light and heat can enter the building.

For commercial buildings, this matters because glass can be a major source of heat gain, glare, fading and comfort complaints.

02 / Solar Spectrum

UV, visible light and infrared heat

Sunlight is made of different types of energy. For window film, the most important categories are ultraviolet, visible light and infrared.

A good window film recommendation depends on which problem needs to be solved. A glare problem, a heat problem, a fading problem and a winter comfort problem may not all call for the same film.

03 / Visible Light Transmission

VLT: how light or dark the glass feels

VLT stands for Visible Light Transmission. It measures how much visible light passes through the glass and film system.

A higher VLT means more daylight comes through. A lower VLT means the glass will appear darker and allow less visible light through.

A high VLT film can keep a space bright and natural looking. A lower VLT film can reduce glare and may improve daytime privacy. However, darker is not always better. The right VLT depends on the room, the glass, the sun exposure and how the space is used.

04 / Solar Heat Gain

SHGC: how much solar heat gets inside

SHGC stands for Solar Heat Gain Coefficient. It measures how much solar heat is admitted through a window system.

SHGC is shown as a number from 0 to 1. The lower the SHGC, the less solar heat is admitted through the glass.

This is one of the most important numbers for solar control window film. A lower SHGC can help reduce solar heat gain in offices, schools, churches, retail spaces, conference rooms, lobbies and other areas with uncomfortable sun exposure.

05 / Total Solar Energy Rejected

TSER: how much solar energy is rejected

TSER stands for Total Solar Energy Rejected. It is commonly used in the window film industry because many people find it easier to understand than SHGC.

TSER is expressed as a percentage. A higher TSER means the glass and film system rejects more total solar energy.

SHGC and TSER are closely related. SHGC tells you how much solar heat is admitted. TSER tells you how much solar energy is rejected. As examples, Solar Gard lists Ecolux 70 at 53 percent TSER and Silver AG 25 Low-E at 77 percent, each on 1/4 inch clear glass.

TSER counts all the solar energy kept out of the building, through both reflection and absorption. It is not the same as how reflective or mirrored a film looks from outside.

06 / Glare Reduction

Glare reduction: making bright rooms more usable

Glare reduction is mostly related to visible light. If a room receives more daylight than occupants can comfortably use, glare can make computer screens difficult to see, cause eye strain and make work areas less comfortable.

Darker films generally reduce more glare because they lower visible light transmission. However, glare is not only about film darkness. It can also be affected by window orientation, time of day, screen placement, interior lighting, wall color and the way the space is used.

07 / U-Factor

U-factor: heat transfer through the window

U-factor, also called U-value, measures heat transfer caused by indoor and outdoor temperature differences.

This is different from solar heat gain. SHGC is about heat from the sun. U-factor is about heat moving through the window because one side is warmer than the other.

The lower the U-factor, the better the window is at slowing heat transfer. This matters most when people are concerned about cold glass, winter comfort, heat loss or sitting near windows during cold weather.

08 / Low-E + Emissivity

Low-E and emissivity: helping glass hold heat better

Low-E stands for low emissivity. Emissivity measures how easily a surface gives off heat as thermal radiation.

Regular clear glass has high emissivity, about 0.84, which means it absorbs and gives off a lot of radiant heat. A Low-E surface has low emissivity, which helps reduce radiant heat transfer. For example, Solar Gard lists Ecolux 70 Low-E film at an emissivity of 0.09.

Low-E coatings and Low-E window films are used to help improve comfort and energy performance. In cold weather, a Low-E surface can help reflect room-side heat back into the occupied space instead of allowing as much radiant heat loss through the glass.

09 / Low-E Surface Location

Why surface numbers matter

On a double pane insulated glass unit, the glass surfaces are numbered from the outside of the building to the inside of the room.

The location of a Low-E coating changes how the glass performs. A Low-E coating on surface #2 is often used to help control incoming solar heat. A coating on surface #3 is often associated with reducing heat loss while allowing more passive solar heat gain.

Low-E window film goes on surface #4, the room side of the glass, where it can help reduce radiant heat loss from the occupied space.

10 / UV Protection + Fading

UV protection helps slow fading, but it does not stop it

Solar Gard architectural films block more than 99 percent of ultraviolet light. UV protection helps reduce exposure to ultraviolet rays and can help slow fading of flooring, furnishings, artwork, merchandise, displays, fabrics and interior finishes.

However, no window film or glass product can completely stop fading. UV is a primary contributor, but fading is also affected by visible light, heat, material sensitivity, artificial lighting, humidity, chemical exposure and time.

Vitro Architectural Glass, citing research used by Lawrence Berkeley National Laboratory, notes that visible light can account for as much as 40 percent of fading, and that heat from absorbed infrared energy can influence the fading process. Depending on the material and exposure, films that also reduce visible light and solar heat may provide additional fade protection.

11 / Solar Absorptance + Glass Safety

Solar absorptance, glass safety, and why glass must be checked first

Solar absorptance measures how much solar energy is absorbed by the glass and film system.

This matters because absorbed heat can increase the temperature of the glass. Under certain conditions, that can increase thermal stress.

Thermal stress is related to temperature differences across the glass. The center of the glass may heat up faster than the edge of the glass hidden under the frame. If the temperature difference becomes too large for the glass to handle, the glass can crack.

A professional recommendation should always start with the glass. The installer needs to know whether the window is single pane, insulated, laminated, tempered, tinted, reflective or Low-E glass before choosing the right product. We explain how this works in Will Window Film Crack Your Glass?.

12 / Film to Glass Compatibility

Choosing a safe film starts with identifying the glass

Not every window film can be installed on every type of glass. Before recommending a commercial window film, the existing glass should be evaluated for compatibility.

A professional evaluation starts with identifying what kind of glazing is onsite. A glass meter helps determine the glass construction and whether Low-E coatings are present. That information is then compared with the manufacturer’s film to glass guidelines before a product is recommended.

Solar Gard’s film to glass guide sorts film and glass combinations into approved, caution (written approval required) and tempered or heat strengthened only, and it requires written approval for any installation over 2,500 square feet.

The safest recommendation is not always the darkest film, the strongest number or the most expensive product. The right film has to fit the customer’s goal and be appropriate for the glass system.

13 / Commercial Film Types

Common commercial window film types

Different window films solve different problems. Some are designed for solar heat control. Some reduce glare. Some improve privacy or appearance. Some help retain broken glass. Others help protect glass from scratching, graffiti or bird strikes.

The right product depends on the building, the existing glass, the customer’s goal and whether the film is compatible with the glass system.

This is why a professional recommendation should not be based on appearance alone. Two films may look similar but perform very differently once installed on the glass.

14 / Film Appearance vs. Performance

Why two films that look similar can perform differently

Two window films can look almost the same on a sample card or installed glass, but still perform very differently.

One film may reduce glare but absorb more heat. Another may allow a lot of visible light while rejecting more infrared energy. Another may be excellent for solar control but not appropriate for certain Low-E glass. Another may provide safety benefits but very little solar heat reduction.

This is why sample appearance alone is not enough. A professional recommendation should consider both the way the film looks and the way it performs on the existing glass.

15 / Dry Out + Curing

Why window film may look hazy after installation

After window film is installed, it is normal for some moisture, haze or small water pockets to be visible during the dry out period.

Window film is installed with a mounting solution. The installer removes as much solution as possible during installation, but a small amount can remain between the film and the glass. That moisture has to dry out over time.

Window film can take several weeks to dry after installation. As a general guideline, allow about 30 days, although drying and adhesion development vary with the film, the glass and the conditions, and thicker safety films or shaded and colder installations may take longer. Separately, Solar Gard recommends waiting 30 days before cleaning newly installed film.

Temporary haze during the dry out period is not the same thing as a failed installation. A professional installer should explain what is normal, what is not, and how long drying may take for the product and the jobsite.

16 / Professional Evaluation

Why a professional evaluation matters

Window film performance numbers are helpful, but they do not tell the whole story. The right film depends on your glass, your building, your sun exposure and what you are trying to improve.

A film that works well for one building may not be the right choice for another. Some customers need heat reduction. Others need glare control, privacy, fade reduction, Low-E performance, safety film or a combination of goals.

A professional evaluation helps make sure the film recommendation is not only useful but also appropriate for the existing glass. That is especially important on insulated glass, Low-E glass, tinted glass, laminated glass, large panes, skylights and heavily shaded glass. AAA Glass Tint’s assessment is free.

Commercial Window Film Guidance

Need help choosing the right commercial window film?

A good window film project starts with understanding your glass, your building and what you are trying to improve.

Whether you need to reduce heat, lower glare, add privacy, protect interiors, improve glass safety or support a commercial construction schedule, AAA Glass Tint can help you compare options and choose a film system that fits your building.

AAA Glass Tint is a commercial window film contractor serving commercial buildings throughout Northern Illinois since 1984. We work with commercial properties, schools, churches, offices, retail spaces, municipal buildings, healthcare facilities, general contractors and property managers throughout the Chicago metropolitan area and Northern Illinois, with select projects in Northwest Indiana, Southern Wisconsin and Southeast Michigan. Every assessment is free.

What are the drawbacks of window film?

Window film has limits. It has to be selected correctly, may change the look of the glass, can reduce some natural light, needs drying time after installation, and is not approved for every glass type. Insulating (Low-E) film improves comfort but is not a replacement for new insulated glass, and no film can fix failed seals, damaged glass, poor frames or every comfort problem in a building.

Can people see through window film at night?

Daytime privacy film usually works best when it is brighter outside than inside. At night, when interior lights are on, visibility can reverse and people may be able to see in. For nighttime privacy, frosted film, decorative film, blinds, shades or a different privacy strategy may be needed. We explain why in Does Privacy Window Film Work at Night?.

How do I choose the right window film?

Start with the problem you want to solve. Heat, glare, privacy, fading, safety, security, winter comfort and appearance may each require a different type of film. A professional should also evaluate the existing glass before recommending a product so the film is appropriate for the glass system.

How long do window films last?

Service life depends on the film type, glass type, exposure, installation quality, interior conditions and whether the film is installed inside or outside. Many commercial interior films can last for years when properly selected and installed. Exterior films and high exposure areas may have shorter service lives. The manufacturer warranty for the specific film is the best reference.

What are common mistakes to avoid with window film?

Common mistakes include choosing film by darkness alone, ignoring glass compatibility, skipping Low-E coating checks, installing the wrong film on high risk glass, expecting privacy film to work the same at night, and assuming security film is unbreakable or bulletproof.

What are the rules for glass film?

The main rules are that the film should be appropriate for the glass, installed according to manufacturer guidelines, and selected for the customer’s goal. Some projects may also involve building standards, school safety requirements, bird-friendly glass guidelines, warranty requirements, or owner and property manager approval.

What are the negative effects of window film?

When the wrong film is selected, possible problems include unwanted appearance changes, too much darkness, glare reflection, thermal stress concerns, poor privacy expectations or reduced performance. These issues are why glass type, exposure, shading and customer goals should be reviewed before installation.

What is the newest trend in window coverings?

In commercial buildings, many customers are looking for glass solutions that improve comfort without blocking daylight. Popular options include high performance solar control film, Low-E retrofit film, decorative privacy film, bird strike prevention film and security film systems for vulnerable glass.

Does window film peel off easily?

Properly installed professional window film should not peel off easily under normal conditions. Peeling is more likely when the glass was not prepared correctly, the wrong film was used, the film was disturbed during curing, the edges were damaged, or the product has reached the end of its service life.

Which is better, frosted glass spray or frosted film?

For commercial glass, frosted film is usually the better choice. It gives a cleaner, more consistent appearance, can be professionally cut or patterned, and can often be removed or replaced later. Spray products are harder to control and usually do not provide the same professional finish.

How do you clean frosted window film?

On factory frosted glass, many standard glass cleaners may be acceptable. On frosted window film, cleaning should follow the film manufacturer’s care instructions. In general, avoid abrasive pads, harsh scraping, strong chemicals and aggressive cleaning that could damage the film surface.

Is ceramic tint better than film?

Ceramic tint is a type of window film, not something separate from film. Ceramic films can offer strong solar performance with a less reflective appearance, but they are not always the best choice for every commercial project. The right product depends on the glass, the performance goal, appearance preference and compatibility guidelines.

Should frosted glass film be installed inside or outside?

Most frosted privacy films are installed on the interior side of the glass, especially for offices, conference rooms, schools and interior glass walls. Exterior installation may be possible with certain products, but it depends on the film, exposure, glass location, durability needs and manufacturer guidelines.