What is Solar Energy ?
The Solar Spectrum is made up of Visible light (47%), UV (2%) and Infrared or NIR (51%).
Visible Light reaching the surface of the earth that can be seen by humans is located between the wavelengths of 400 and 780 nanometers (nm) in the spectrum. It accounts for 47% of the overall solar energy from the sun but only 43% of the Heat. As the Visible light hits a surface the heat builds on that surface.
UV, or Ultraviolet Light falls between 100 nm to 380 nm and is not visible to the human eye. This energy is highly energetic and destructive (Skin Cancer, Burning, Fading) but, when considering heat the amount of energy it carries is small compared to the amount of energy contained by visible and infrared light. This form of light only accounts for 3% of the heat.
Last, the remaining energy is Infrared Radiation. The near infrared portion of the solar spectrum runs from approximately 780 nm to 2,500 nm and carries about 51% of the solar energy - just under half of the total solar energy. Although it accounts for 53% of the heat from the sun!
The Solar Spectrum is made up of Visible light (47%), UV (2%) and Infrared or NIR (51%).
Visible Light reaching the surface of the earth that can be seen by humans is located between the wavelengths of 400 and 780 nanometers (nm) in the spectrum. It accounts for 47% of the overall solar energy from the sun but only 43% of the Heat. As the Visible light hits a surface the heat builds on that surface.
UV, or Ultraviolet Light falls between 100 nm to 380 nm and is not visible to the human eye. This energy is highly energetic and destructive (Skin Cancer, Burning, Fading) but, when considering heat the amount of energy it carries is small compared to the amount of energy contained by visible and infrared light. This form of light only accounts for 3% of the heat.
Last, the remaining energy is Infrared Radiation. The near infrared portion of the solar spectrum runs from approximately 780 nm to 2,500 nm and carries about 51% of the solar energy - just under half of the total solar energy. Although it accounts for 53% of the heat from the sun!
Transmission, Reflection, and Absorption in Solar Energy
It is important to understand transmission, reflection, and absorption when discussing the behavior of films in the infrared portion of the solar spectrum. Reflected energy never enters a building through a window, nor does it enter the glass- it is ejected away from the building without affecting the temperature of either the glass or the interior. 100% of transmitted energy passes through a window and becomes heat gain inside of a home. Absorbed energy takes a more complicated path in the window system. Absorbed energy is taken into the pane of glass, thus heating up the window and its frame. Some of this absorbed energy that is stored in the window is radiated back outdoors, while some of it enters the home. |
Solar Heat Gain Coefficient
This is important because the Solar Heat Gain Coefficient (SHGC) takes into account the effects of all three phenomena. Infrared reduction numbers currently reported in the industry refer only to energy that is not transmitted, and ignore the heating effect of absorbed radiation. This is another reason the SHGC is the superior and industry recognized performance of a window, since not only does it take into account the full solar energy spectrum, it accounts for the harmful effects of absorption on home interior temperatures.
To perform an approximate conversion:
Use the formula SHGC = SC*0.87 to convert between SHGC and SC
Total Solar Energy Rejection
The TSER is the "true" heat rejecting value for a film, because it takes the entire solar spectrum into account (infrared is only 49% of the solar energy anyway), and also includes the effects of absorption. It is recognized by Energy Star, utility companies, and U.S. and Canadian governments. They only recognize SHGC, TSER. They do not recognize IRR. The sum of the TSER (Total Solar Energy Rejection, in decimal form) of a glazing system and its SHGC value is 1; therefore,
1 - TSER = SHGC
Thus, if the TSER of a specified film/glass combination is 58%, then 1 - .58 = .42, which is the SHGC of the window.
Comparing Window Tinting Film
Window Films act as a filter reducing varying percentages of each part of the Solar Spectrum. When comparing films, it is best to compare films with the same VLT (visible light transmission). When you choose your window film, once you decide the VLT, the color, you can focus Total Solar Energy Rejection, which tells you which film reject more solar energy. A film with a high TSER (Total Solar Energy Rejected) could be darker in color or highly reflective.
This is important because the Solar Heat Gain Coefficient (SHGC) takes into account the effects of all three phenomena. Infrared reduction numbers currently reported in the industry refer only to energy that is not transmitted, and ignore the heating effect of absorbed radiation. This is another reason the SHGC is the superior and industry recognized performance of a window, since not only does it take into account the full solar energy spectrum, it accounts for the harmful effects of absorption on home interior temperatures.
To perform an approximate conversion:
Use the formula SHGC = SC*0.87 to convert between SHGC and SC
Total Solar Energy Rejection
The TSER is the "true" heat rejecting value for a film, because it takes the entire solar spectrum into account (infrared is only 49% of the solar energy anyway), and also includes the effects of absorption. It is recognized by Energy Star, utility companies, and U.S. and Canadian governments. They only recognize SHGC, TSER. They do not recognize IRR. The sum of the TSER (Total Solar Energy Rejection, in decimal form) of a glazing system and its SHGC value is 1; therefore,
1 - TSER = SHGC
Thus, if the TSER of a specified film/glass combination is 58%, then 1 - .58 = .42, which is the SHGC of the window.
Comparing Window Tinting Film
Window Films act as a filter reducing varying percentages of each part of the Solar Spectrum. When comparing films, it is best to compare films with the same VLT (visible light transmission). When you choose your window film, once you decide the VLT, the color, you can focus Total Solar Energy Rejection, which tells you which film reject more solar energy. A film with a high TSER (Total Solar Energy Rejected) could be darker in color or highly reflective.