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What’s window film?
Generally, window film provides specific personal and property protection from the effects of the sun as well as added safety and security in the events that result in broken glass.
The concept of window film for use in solar control flat glass application dates back to the early 1960s. The original film design objective was to control the heating and cooling imbalances that result from solar loading. Such early films were found to reflect solar radiation back from a window, preventing the warming of inside surfaces normally hit by direct sunlight while still allowing vision through the glass.
As the window film concept was developed and improved upon, a demand developed for colored sun control films that would complement architectural design. Coloration of film was achieved through various means to produce colors such as bronze, gray, gold, amber, etc.
The energy crisis of the early 1970s prompted an interest in another aspect of window film use: the reduction of heat loss to the outside. It was discovered that polyester film tended to absorb and reradiate long wave infrared heat rather than act as a transparent medium. Through experimentation, new film materials and constructions were developed that enhanced this characteristic. These films greatly improved heat retention within a room’s interior. The efficiencies of solar control window films are closely related to local weather conditions, building orientation, window size, and other factors such as exterior shading conditions. However, with escalating energy costs, products such as window film are increasingly valuable as an investment for commercial and residential owners and commercial facility managers.
There are many types and constructions of solar control and safety window films. These films are considered in the building industry to be “retrofit” products; that is, products to be applied to existing buildings as opposed to use in new construction. In their simplest forms, window films are composed of a polyester substrate to which a scratch resistant coating is applied on one side; a mounting adhesive layer and a protective release liner is applied to the other side. When the release liner is removed, that side of the film with the adhesive is applied to the interior surface of the glass.
What’s the solar energy?
Solar energy is a form of electromagnetic radiation. All forms of solar energy can be expressed as a wavelength, which is the measure of the length of a full cycle in a repeating electromagnetic curve. The solar energy that enters into the earth’s atmosphere is split into three bands by wavelengths; the ultraviolet (UV), visible (VIS) and infrared (IR) bands.
The UV Band: is measured between 100-400 Nanometers and are the wavelengths most responsible for fading or sun damage to carpets, drapes, fabrics, upholstery, etc. The UV band is the one that tans the skin and can also contribute to certain types of medical problems when over exposed, such as certain types of skin cancers. The UV band accounts for 3% of the solar spectrum.
The Visible Band: is measured from 380-780 Nanometers. This is the only part of the solar spectrum actually seen with our eyes and is the most intense in the entire solar spectrum. The visible band accounts for 44% of the solar spectrum.
Infrared energy is measured from 780-50,000 Nanometers and is divided into the near infrared (NIR) and the far infrared (FIR) bands. Infrared accounts for 53% of the solar spectrum. The Near Infrared is measured from 780-2400 Nanometers and is the “heat band.” We do not see it, but are aware of it and sense these wavelengths as heat. The near infrared band accounts for only about 3.2% of the entire infrared range. The Far Infrared is measured from 2400 to 50,000 Nanometers. This band is beyond the near infrared range and accounts for 96.8% of the total infrared band. There is no solar energy in the far infrared band. The far infrared band has nothing to do with solar heat gain but is crucial in containing heat loss.
Window films are frequently referred to as “solar control” window films. However, there is a great deal of confusion and misunderstanding about “solar energy rejection,” particularly in the infrared range. The International Window Film Association (IWFA) does not recognize “IR” rejection as a valid measurement or expression of any window film’s efficiency in reducing total solar energy or for comparing one film to another. Please note, the impression being created by some brands is that the percentage of “IR” rejection means the same as “total solar energy reduction”, which simply is not accurate.
Is UV harmful?
Ultraviolet radiation is measured between 100-400 Nanometers and accounts for about 3% of the total solar spectrum. Despite the small percentage of the total solar energy, ultraviolet radiation plays an important role in both the energy balance and chemical composition on earth, including the production of vitamin D in humans. However, there are some serious negative effects of ultraviolet radiation as well. Ultraviolet rays are commonly associated with fading or sun damage to all types of interior furnishings, such as carpets, draperies, upholstery and furniture, etc. In addition, UV rays tan the skin but are also directly related to various types of skin disorders, cancers and eye problems such as cataracts.
Ultraviolet radiation is divided into three classifications:
UVA, which is measured between 320 to 400 Nanometers, is about 1,000 times less in intensity than UVB rays but between ten to one hundred times more prevalent in the earth’s atmosphere. UVA are the longest of the ultraviolet wavelengths and therefore passes through material objects, including glass, far easier than the other UV rays. UVA also penetrates skin more deeply than the other UV wavelengths and interacts with organic molecules, which promotes the development of various types of skin cancers.
UVB which is measured between 290 to 320 Nanometers, are the wavelengths most responsible for causing a reddening of the skin or sunburn, as well as “welder’s flash” and “snow-blindness” which are irritations of the cornea caused by overexposure to excessive light.
UVC, which is measured between 10 to 290 Nanometers, are the shortest UV wavelengths and potentially the most lethal to human life. Fortunately, virtually all of the UVC radiation is blocked out by the earth’s atmosphere, primarily the ozone layer, before it reaches the earth’s surface.
While it is virtually impossible to completely avoid all contact with ultraviolet radiation, there are preventative steps that can be taken to reduce or minimize the risks of overexposure, such as wearing long and closely woven clothing, proper sunglasses, wide brim hats and sun-screens with a sun-protection factor (SPF) of 15 or higher on all exposed skin.
In most cases, standard plate glass or automotive glass is fairly efficient in preventing UVB radiation from passing through it, which is why it is difficult to get a sun tan behind glass. However, a very high percentage of the UVA radiation still penetrates standard glass and can significantly contribute to skin problems. An example of this is that there is a much high ration of skin malignancies on the driver’s exposed side of the body as opposed to the interior side with is better protected.
Will window film really stop fading of fabrics?
There are six factors affecting fabric fading:
1. Ultraviolet Light (40%)
2. Visible Light (25%)
3. Heat and Humidity (25%)
4. Chemical Vapors (including ozone) (10%)
5. Age of Fabric
6. Dye Fastness
Clear single pane glass (1/8″ to 1/4″) will reject 23-28% of the ultraviolet light from the sun. Insulated glass is slightly better, rejecting 36-41%. Window films installed on glass reject 95-99% of solar ultraviolet light. Different types of clear glass and window systems will reject 13-29% of the solar heat. With window films, 80% solar heat rejection can be obtained.
No window film can eliminate fading. It can, however, offer maximum protection from fading due to solar ultraviolet light and solar heat.
How long will film last?
The effective life of window film will vary by the type of film, type of glass, window construction, compass orientation of glass, and in which part of the world the building is located. There are documented cases of film lasting 12 to 22 years or more in some instances. This should not, however, be assumed to be the normal expected life.
All quality window films for residential and commercial use are warranted by the film manufacturers for a minimum of five years (certain products may have extended coverage). The warranty includes an address to contact the manufacturer directly should any questions arise either before or after the installation of the window film.
How should I clean my windows after film is applied?
Windows with film applied are easily cleaned without damage to their appearance as long as a few common-sense guidelines are followed:
1. Use a soft clean cloth, soft paper towel, or clean synthetic sponge.
2. Use a soft cloth or squeegee for drying the window.
3. Use any normal glass cleaning solution which contains no abrasive materials.
The availability of scratch resistant coatings as a standard feature of quality films has virtually eliminated the need for extra special precautions in cleaning.
Will window film kill my house plants?
In most cases if a house plant is already receiving adequate light the use of window film will not harm it. New growth or flowering may be retarded, and, for a few days, a plant may go into a state of shock while it adjusts to the light change. If a particular plant normally wilts by the end of a sunny day, it will actually thrive better with film installed. Although there are some obvious guidelines in determining what, if any, effect window film will have on a plant (for instance, dark green plants need less light than lighter colored ones), there is one sample test which can be done prior to film installation: merely move the plant to an area with less sunlight for a few days. In addition, most nurseries or local agriculture agencies can advise you whether a particular plant needs closer to maximal or minimal light.