Design & Decor

Working the Window

What to look for when considering heat-blocking window film that won’t block light.

According to residential energy experts, as much as 40 percent of a home’s cooling requirements is because solar energy enters through glass; therefore, the best place to stop that heat and reduce air conditioning costs is at the window. But the most energy-efficient window film is not necessarily the film that blocks the most heat.

Conventional tinted and reflective window films do block heat, but they also block light. In some cases, highly reflective window films with metalized heat-reflective coatings block as much as 85 percent of the visible light outside from entering the inside of a home or condo. The result is an environment in which natural levels of light are permanently excluded.

Studies conducted by the U.S. Department of Energy and others document a relationship between low levels of natural light and less-than-optimum well-being. Occupants of darkened homes feel less energized, often suffer more illness and are less active and productive than those in homes benefiting from natural illumination.

In addition, conventional window films lessen the transparency and often change the external appearance of existing glass. The subsequent darkened interiors often require increased lighting, which not only adds cost, but as a generator of heat, might result in more, not less, use of air conditioning, defeating the cost-saving benefit of applied window film in the first place.

Back to Basics

Homeowners desire and need windows for natural light and a connection with the outside environment, but even a small amount of glass on the south or west side of a home or condo can result in uncomfortable overheating and increased air conditioning and other costs.

While it is relatively easy to manufacture tinted and reflective film that blocks heat, it is quite another to produce what is called spectrally selective window film that is capable of blocking undesirable heat while simultaneously transmitting desirable light.

The good news is that several professionally applied, spectrally selective window films are available in the Kansas City area for residential use. The bad news is that not all transmit visible light equally well. The ideal film would be totally clear yet able to significantly block unwanted solar heat and reduce glare. A true spectrally selective film transmits at least 70 percent of visible light. If a window film looks tinted and not clear, it is not optimally selective in the all-important category of visible light transmission.

When faced with a choice between a tinted or reflective film that blocks more heat and a spectrally selective film that blocks less heat but transmits more light, the latter is often the best choice. An increasing number of electric utilities encourage homeowners to choose a window film based on its luminous efficacy constant, a measurement of the ability to simultaneously block heat and transmit light. Those utilities offering rebates to homeowners who buy heat-blocking window film often grant larger rebates to those spectrally selective films with luminous efficacy constants over 1.0.

Less-expensive conventional window films have a shorter payback compared to more-expensive spectrally selective films. But the cost of extra energy used for lighting and air conditioning operation because of a conventional film’s inability to transmit sufficient visible light makes the payback for conventional film and spectrally selective film comparable. Given rising electricity and natural gas rates, the rate of payback for spectrally selective film is always improving — averaging about four years. Factor in the issues of comfort and well-being, as well as a home’s appearance, and it’s clear that spectrally selective window film is the preferred choice.

* The lower the shading coefficient, the lower the solar heat gain.

V-Kool applied window film is reducing the cost of air conditioning at Blockbuster Video stores in Lawndale and Northridge and at Chevron service stations from San Jose to Redding.

V-Kool is a trademark of V-Kool, Inc., Houston, TX, a sales and marketing distribution company of heat reflective applied films for residential and commercial architectural, automotive and specialized vehicular applications.

V-Kool, proudly participates in Energy Star® a voluntary partnership among the U.S. Department of Energy, the U.S. Environmental Protection Agency, product manufacturers, local utilities and retailers. Energy Star partners promote energy efficient products using the Energy Star logo and by educating consumers about the benefits of energy efficiency.

V-Kool's solar control films are manufactured by Southwall Technologies, Palo Alto, CA, whose window film technology was recognized by Popular Science as one of the 100 greatest inventions of the past millennium.

Return to Press Release main page