Understand The Solar Optical Properties Of Window Film Used For Tinting

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The primary objective of using window film is for energy saving and conservation of heat and other resources. It is the complex technology of these window films makes the equation simple. If you keep out the heat from your room, then less energy will be required and spent to cool the building in the summer season using your air conditioning. On the other hand, during the winter, if you control and reduce the heat loss from the inside, you will reduce the workload on the heating system. Thanks to the high-efficiency window films.

According to research, most of the heat is lost or gained through windows, but that does not mean you will keep it shut always. If you do so, then the primary objective and functionality of the windows will be compromised. Your rooms will be stuffy and uncomfortable due to poor ventilation and circulation of air. It will also be unhealthy and unhygienic. The easy and effective solution to manage and control amount of heat inside a room is by using window films.

Most effective solution

Using window films in your car, office or home is the cheapest and cleanest way to conserve energy in the most environmentally friendly way. Ideally, it is the solar optical properties of the window films that enable it and facilitates in saving energy. Moreover, on this planet, the most conscious energy is energy that you do not need to use. The three most significant and biggest areas in your building that provides you with such an opportunity to conserve energy are lighting, HVAC, and the entire building envelope.

Most people start with conserving energy by reducing the use of lights. This is because it is easy, quick and typically the most cost-effective way.

The envelope of the building is probably the most overlooked opportunity. Ideally, it is the most significant option to save money and energy both.

Simple as it may sound, you can put in a little effort and money in window filming, turning off the light when not necessary, avoiding unnecessary trips, and using the HVAC as and when required can help you to save a lot of energy. These are the most cost-effective, simple and passive ways to preserve energy and effectively offset greenhouse gas emissions.

Measurements to consider

There are typically five key measurements or metrics to consider when you select a window film. These are also called the solar optical properties of the film. These are:

  • Visible light
  • Transmitted visible light
  • Visible light that is reflected in the interior
  • Visible light reflected in the building exterior and
  • The Solar Heat Gain Coefficient or SHGC.

All designers, property owners and Commercial Window Tinters must understand all of these solar optical properties of the window film. It will help one and all to select the specific type of window film that will meet the unique needs of an individual.

The variance of solar energy 

The solar optical properties of a film of a film vary and have a significant role to play in its ultimate functionality. Each of these properties can be explained in details along with its different groups and sub-groups as under:

  • Total Solar Energy: This is the entire energy found in a solar spectrum that reaches to the earth’s surface and all living and non-living things on it. This spectrum includes UVA and UVB, the infrared energy that may range up to 2500 nm and visible light. However, the common concept of total solar energy happens to be the heat in it.
  • Transmitted Total Solar Energy: This is the amount of solar energy that transmits or passes through the glass on the windows or any other place in the building.
  • Reflected Total Solar Energy: This is the specific amount of total solar energy reflected off the glass and is directed back outside the building. This means the heat and light energy cannot enter into the building.
  • Total Solar Energy Absorbed: This metric measures the total amount of energy absorbed by the glass. This, in turn, heats up the glass so much so that it feels hot when you touch it. This heat absorbed and stored by the glass is then reradiated back into the room in small amounts, though the majority of the absorbed heat is kept out of the room.

Similarly, there are different types of visible light as well. The visible light is that part of the solar spectrum that you can see, meaning it falls on an object and gets reflected. Typically it contains all the colors of the spectrum and therefore appears to be white, remember Newton’s disc? This visible light ranges from 370 nm up to 770 nm approximately. The three varieties in visible light are:

  • Transmitted – This is the amount of visible light that passes just like the heat through the glass inside the building. The volume of light entering the room will depend on how dark or light the window film is.
  • Reflected Interior – This is the amount of visible light in the room that is reflected off the walls and other surfaces of the room’s interior after entering through the window glass. You can see this reflected light when you look out of the building while standing inside it. If the window film has a higher reflectance value, the window will look more like a mirror from inside.
  • Reflected Exterior – This measures the volume of visible light reflected off the window’s exterior surface. You can see this when you stand outside your building and once again a higher reflectance value will make the window look like a mirror from the outside.

Other properties to know

To understand the solar optical properties of the window films, there are a few other properties you must know and consider. These factors play their role according to the season and dimensions of the room and the glass on which you install the film.

  • U factor is one such property that affects the heat transfer, especially during the winter season due to temperature variance inside and outside the building. This factor represents the amount of heat that passes through one sq. Ft. of glass in an hour. This is measured for every single degree temperature difference in the outside and inside of the building. If this has a lower value, it signifies that a lesser amount of heat is passing through the glass and vice versa. This factor is desirable when you want to retain the temperature inside the room in cold climatic conditions.
  • The emissivity of the window film is a factor that determines the ability of it to reflect the infrared energy of the solar spectrum. This will eventually control and determine the amount of heat energy that will be allowed by the film to pass through it into the room. Low emissivity of the film or glass means it will emit a lot of heat back into your room, once again helping you to maintain the desired temperature in cold climates.
  • Ultraviolet Light Rejected – This factor controls the amount of UV energy of the sun that is blocked by the film. The film may either absorb it or reflect it but will never allow it to enter the room.

Glare reduction properties

The window films also have specific properties that reduce the sun’s glare. These are:

  • Luminous Efficacy – This is the ratio of solar heat to visible light transmission for a window film. If a film has higher luminous efficacy then under a given VLT it will be very effective in high heat rejection.
  • Shading Coefficient – This is another ratio that measures the heat passing through any clear and un-filmed glass as compared with a filmed window. In this case, a lower rate will mean better heat rejection.
  • Solar Heat Gain Coefficient – This is a specific metric that is very much similar to the shading coefficient. The only difference is that this value also represents the amount of energy that is reradiated back to the room through the glass when it heats up due to increased absorption. This is the primary indicator of the effectiveness of the film in rejecting solar energy. Once again, a lower coefficient will mean better heat rejection.
  • Infrared Rejection – This is another significant factor that indicates the amount of infrared energy of the sunrays that the window film can block. The value indicates the entire infrared region of the solar spectrum ranging from 780 nm to 2500 nm roughly. Even if the window film absorbs or reflects the infrared energy, its ability will be measured in this value.

All these factors and properties of a window film will serve as your ultimate goal of total solar energy rejection to regulate the internal temperature of your building. Commonly known as heat rejection in the window film industry, this is the primary objective of the films and determines its effectiveness and functionality.

It goes without saying that you must always buy window films from reputed and reliable manufacturers and avoid any cheap alternatives. It is your comfort and health on the line with which you should not be negligent.

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