Heat Shield Spectrally Selective Window Films

The information provided below was designed to help our customers understand how Spectrally Selective window films stop harmful infrared heat and ultraviolet radiation while enhancing your view, both day and night.

The sun’s energy is known as solar radiation. It is also called the solar spectrum. The solar spectrum has 3 components- ultra violet radiation, visible light and infrared heat. The visible light is the only component that humans can see. It is also sometimes called daylight. The visible light is what causes the colors of the visible light spectrum. Window films that block most of this component of solar radiation will cause the space to be very dark and lacking of bright colors. Studies have shown that employees spending 6 to 8 hours per day in dark spaces are much less productive and call in sick more than employees in naturally day lighted areas. UV energy has the shortest wavelength. Visible light is the middle wavelength and infrared has the longest wavelength. You can think of this as being similar to the ripples in a pond after you toss a pebble. The ripples that are closest together would represent the UV, the middle ripples would be the visible light and the ripples that are furthest apart would be the infrared. Infrared is responsible for 53% of the suns energy, visible light is responsible for 44% and UV 3%.



 

Here is a plot that shows the amount of energy versus wavelength for the sun. The wavelength is given in dimensions of nanometers (nm), which is one billionth of a meter.

The Solar Spectrum above looks like piles of white sand. The piles of sand represent the solar spectrum or what we know as sunlight. Unfiltered sunlight is intense. Skin cancer, sun fading and heat load are all problems associated with this brutal sunlight.

Let’s look at one of the most important numbers in the window film industry, TSER or Total Solar Energy Rejected. This number represents the total solar energy (UV + Visible Light + Infrared Heat) being rejected by a particular filmed glazing system. Since the solar energy above looks like piles of white sand a TSER of 50% would mean you removed half the sand. The key point to remember is that it does not tell you which piles of sand were removed but only that half is now gone. TSER does not tell you which wavelengths are being rejected, just the total amount of solar energy removed. Another very important term used in the glass and film business is SHGC or Solar Heat Gain Coefficient. The difference between SHGC and TSER is very simple: TSER = (1 - SHGC). So if you have a TSER of 40%, the SHGC = .60. The TSER can be thought of as the percentage of solar energy rejected (higher being better) while the SHGC is the amount of solar energy being transmitted (lower being better).

Most people would think the film with the highest TSER is the best performing product. TSER can always be increased by making the film darker and more reflective. Remember that TSER looks at UV, Visible Light and Infrared Heat. To make apples to apples comparisons, you need to look at films with the same or similar visible light transmissions. As a quick example, here are two charts that show glazing systems with a TSER of 50%, however one of these systems has a visible light transmittance (VLT) of 80% while the other has a VLT of 20%. These films look identical from TSER, but the 80% (VLT) film is a much higher performing film because it is spectrally selective, i.e. blocks out more infrared heat than visible light. If we took the 80% VLT film and tinted it down to the same 20% VLT level, without rejecting any additional UV or Infrared energy, then the TSER number would increase to approximately 80%. Luminous Efficacy was created to help people make this sort of comparison because it is defined as the VLT divided by the shading coefficient. Special window films that score 1.0 or greater are “Spectrally Selective”. The higher the Luminous Efficacy, the better you are doing at rejecting the IR heat and letting the visible light through. This is important since recent studies have shown that 30 - 40% of the total electricity bill for commercial buildings is caused by interior lighting. Day lighting (the practice of placing windows, or other openings, so that, during the day, natural light provides effective internal illumination) is also a big concern and we believe you will hear a lot more on this subject in the future.

Another quick point to make is that the California energy commission pays more in energy rebates for spectrally selective films than is does for traditional metalized technology.

This film below (the turquoise colored curve) is spectrally selective because it lets in maximum light and filters out maximum UV and infrared heat. Spectrally Selective films are the most difficult films to produce because they are spectrally tuned to let in the light and block out the heat.

Finally… a window film that is clear yet blocks harmful Ultra Violet radiation and Infrared heat. The perfect solar control film for any climate is "Heat Shield", available only through Heat Shield USA 720-230-8468

This film here (the turquoise colored curve) is a traditional metal film that gets its performance from blocking most of the visible light component of the spectrum. This is why most traditional metalized products are dark and reflective. Notice how much infrared heat is transmitted through this film. This film is not “Spectrally Selective” because it does not block more infrared than visible light. It actually blocks more light than heat! From a manufactures point of view this is the easiest and least expensive film to make. Visible light is what we want in our homes and business’s. We recommend films in the 70% VLT range and above. Be a wise consumer and do your homework. Visible light transmission is defined within NFRC 200 - 2004. VLT is the total amount of the visible light, i.e. sunlight (380nm - 780 nm), that transmits through your filmed window.

Nano-ceramic window film is the single most cost effective way to “Go Green” and saves on the continually rising energy cost associated with today’s economy. Clear spectrally selective window film does not change the appearance of the existing glass, allowing its application on the entire facility or on as few windows as necessary to deal with a localized solar heat gain issue.

19 of the 20 hottest years since 1986 have been in the last 20 years. The good news is that with Heat Shield Window Film you can help reduce using air conditioning, the energy it demands – and its effects on the environment! (Data from www.nasa.gov)

Solar Heat Gain, or what we know as natural sunlight, consists of three elements: 53% Infra Red (IR) radiation, 44% Visible Light (VL) and 3% Ultra Violet (UV) radiation.

UV radiation is highly damaging. It is widely acknowledged that the sun's UV radiation can cause skin cancer and cataracts through prolonged exposure. Similarly, this radiation is the primary cause of fading to home and office interior fabrics and colored components.

Visible light, on the other hand, is absolutely essential. It is the visible light that allows us to see.

To effectively protect you from the sun, window films need to reject UV radiation and Infrared radiation, while allowing for as much visible light transmission as possible. This intelligent filtering, or spectrally tuning is made possible by Heat Shield’s nano-ceramic technology and is known world wide as spectrally selective window film.

 

BTU Meter

a device that measures solar energy intensity and gives solar intensity in either W/m² or BTU/ft².hour. It is used to compare the solar intensity entering through glazing with and without solar control window film.

 

 

BTU-British Thermal Unit

The amount of heat energy required to raise the temperature of one pound of water one degree Fahrenheit. 1 BTU = 252 Calories (Cal).

 

 

Infra-Red Radiation

Wavelengths of electromagnetic radiation from 780 nm to about 60 000 nm; near infra-red is about 780-2500 nm and far infra-red is about 2500-60 000 nm. Solar radiation contains a large amount of infra red radiation between 780 nm to 2500 nm. This type of radiation is not radioactive.

 

 

Luminous Efficacy

A measure of how effective a glazing product is in rejecting solar energy but retaining good visible light transmission. A number greater than 1.0 indicates the film or glazing unit is "Spectrally Selective," blocking more of the near infrared than the visible light components of the solar spectrum.

 

 

Machine Direction (MD)

The machined direction along the entire length of a roll of window film.

 

 

Metalizing

A manufacturing process used to deposit a metal onto polyester film surfaces by evaporation; the metal is usually Aluminum. Metalized window film provides excellent solar control.

 

 

Neutral Color

Usually refers to films that have a high Color Rendering Index (> 90). See Color Rendering Index.

 

 

*Nanometre or nm

One millionth of a millimeter or 0,000000001 m.