Glossary

Absorptance:
The amount that is taken into a medium.

BTU-British Thermal Unit:
The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit. 1 BTU = 252 Calories (CAL)

Deposition Process:
A form of physical vapor deposition (PVD) often used for deposition of metal films. Film is drawn through a tank containing metal ingots where a vacuum is created by reducing the pressure in the tank, which is then flooded with argon gas and the ingots are heated. The heat causes the metal to give up particles that migrate to the film's surface.

Dyed Film:
Window film that uses either a submersion process or a dyed adhesive process to deposit dye onto its surface to achieve the qualities and look of tinted film.

Emissivity:
The measure of surface's ability to absorb or reflect far-infrared radiation. The lower the emissivity rating, the better the insulating qualities of the window film/glass system.

Hybrid Film:
Window film that is made up of a combination of metallic film and dyed film to achieve the qualities and look fo tinted film.

Infrared Light:
A form of electromagnetic radiation with wavelengths between 0. 7 micrometers (0.0007 millimeters) and 1 millimeter. These wavelengths are longer than those of visible light, but shorter than those of microwaves. (The prefix 'infra' means 'below; infrared refers to radiation below the frequency of red light.) Infrared light is primarily thermal radiation, and we can think of this as being heat.

Metallic Film:
Window film that uses either a sputtering process or deposition process to deposit metals onto its surface to achieve the qualities and look of tinted film.

Polyester Film:
Polyesters are made from chemical substances found mainly in petroluem and are manufactured in fibers, films, and plastics. Polyester film (PETF) is a semi-crystalline film used in many applications such as videotape, high quality packaging, professional photographic printing, X-ray film, floppy disks, etc.

Reflectance:
The amount that is bent or sent back by a medium.

Shading Coefficient:
The ratio of solar heat gain passing through window film to the solar heat gain that occurs under the same conditions if the window were made of clear, un-shaded double strength window glass. The lower the number, the better solar shading qualities of the window film/glass system.

Solar Absorptance:
The percent of incident solar radiation that is absorbed by the window film/glass system. The lower the number, the less solar radiation absorbed. Solar Heat Gain Coefficient:
The ratio of total solar heat passing through a given window product relative to the solar heat incident on the projected window surface at normal solar incidence (I.E. perpendicular to the glazing surface). The lower the coefficient number for a particular window film/glass system, the better it is able to reduce heat.

Solar Reflectance:
The percent of incident solar radiation that is reflected by the window film/glass system. The lower the number, the less solar radiation reflected.

Solar Transmittance:
The percent of incident solar radiation that is transmitted through the window film/glass system. The lower the number, the less the solar radiation transmitted.

Sputtering Process:
A form of physical vapor deposition (PVD) often used for deposition of metal films. Sputtering involves knocking metal atoms off a disc of pure metal with charged, energetic, chemically inactive atoms called ions (from a plasma). The metal atoms will re-deposit and build on top of polyester film.

Total Solar Absorption:
The ratio of the amount of total solar energy absorbed by a glazing system to the amount of total solar energy falling on the glazing system. Solar absorption is that portion of total solar energy neither transmitted nor reflected. Since solar transmittance and solar reflectance are measured directly, the following equation should be used in calculating solar absorption. Solar absorption =1.00 - (solar transmittance) - (solar reflectance).

Total Solar Energy Rejected:
The percent of total solar energy (heat) rejected by the window film/glass system. The higher the number, the more total solar energy (heat) rejected.

Total Solar Reflectance:
The ratio of total solar energy which is reflected outward by the glazing system to the amount of total solar energy falling on the glazing system. On filmed windows this reflectance is a function of the side of the film facing the window surface. Value is usually expressed as a percent.

Total Solar Transmittance:
The ratio of the amount of total solar energy in the full solar wavelength range (300-2,100 nanometers) that is allowed to pass through a glazing system to the amount of total solar energy falling on that glazing system. Value is usually expressed as a percent.

Transmittance:
The amount that is allowed to pass through a medium.

U-Factor:
The overall heat transfer coefficient of the glazing system, U -Factor is a measure of the heat transfer that occurs through the glazing system, and its outer and inner surfaces. This value is a function of temperature, and is expressed in BTU per square foot per hour per degree Fahrenheit (BTU/ sq. ft./hr. degrees F). The lower the U- Factor, the better the insulation qualities of the glazing system.

U-Value:
The ability for heat to transfer through 1 square foot of window film for each 1° fahrenheit difference in temperature. It is dependent upon the local climate or environment that the window is located in effects the level of heat transfer and the rate; in summer, heat transfers from the outdoor air to indoor air. In winter, heat transfers from indoor air to outdoor air. The lower the U-Value, the better insulating qualities of the window film/glass system.

Ultraviolet Light:
Light having a shorter wavelength and higher energy than visible light. Ultraviolet light is potentially damaging to library, archive and museum objects. Removing UV light can reduce the rate of deterioration. Certain acrylic sheets have UV filtering chemicals built into them.

Ultraviolet Transmittance:
The percent of ultraviolet light (UV) that is transmitted by the window film/glass system. The lower the number, the less ultraviolet transmitted.

Visible Light:
Electromagnetic radiation at wavelengths which the human eye can see. We perceive this radiation as colors ranging from red (longer wavelengths; ~ 700 nanometers) to violet (shorter wavelengths; ~400 nanometers).

Visible Light Absorptance:
The percent of total visible light that is absorbed by the window film/glass system. The lower the number the less visible light absorbed.

Visible Light Reflectance:
The percent of total visible light that is reflected by the window film/glass system. The lower the number the less visible light reflected.

Visible Light Transmittance:
The percent of total visible light that is transmitted through the window film/glass system. The lower the number the less visible light transmitted.