Technical parameters of automotive window films

By 2016-02-24 Egyéb No Comments

TSER, TST? VLT, VLR? What do all of these mean? What is the significance of technical parameters in the case of window films?

There is a lot of confusion in the marker because of the exact meaning of technological parameters. Which of them is an indication of the heat protection of the window film? Why are there several energy values? This is a short survey of such issues.

The situation is mush easier with automotive window films than with architectural ones, where the type of the glazing system is a crucial factor. With car windows, basically there is only one kind: a single-layer or glued tempered glass. Technical parameters can be categorized into three large groups: values related to heat protection, to light, and others.

First of all, let’s take a look at heat protection parameters. The energy reaching a surface can be divided into three parts. Firstly, the part that is reflected from the surface – this is called Total Solar Energy Reflected (TSR). Secondly, the part which is transmitted by the surface, which is named Total Solar Energy Transmitted (TST). The third parameter is Total Solar Energy Absorbed (TSA), which corresponds to the energy absorbed by the surface. Evidently, the sum of these three parameters is equal to the amount of energy which originallyreached the surface. It is also important to know that absorbed energy doesn’t disappear, but it is radiated at a different wavelength by the surface, thus increasing the amount of trasmitted and reflected energy. There is a further parameter showing the resultant of the above: Total Solar Energy Rejected (TSER). This value provides the most comprehensive picture about the heat protective function of window films from an energy perspective. Please note: sometimes this parameter is mistakenly confused with Total Solar Energy Reflected. If, however, you are interested in the amount of energy which will be transmitted, look at Total Solar Energy Transmitted, which is a good indication of how much less energy will enter the car. Anyway, this is the best indicator for automotive window films, as absorbed energy doesn’t play a role nearly as important as with architectural films.

As an example, let’s see a dyed and a dyed-metallized window film, as well as one with nanotechnology.

Dyed window film with 20% light transmission:
TSER – 42%
TST – 45%
TSR – 6%
TSA – 49%

Dyed-metallized window film with 20% light transmission:
TSER – 55%
TST – 27%
TSR – 8%
TSA – 65%

Nanotechnology window film with 20% light transmission:
TSER – 62%
TST – 15%
TSR – 7%
TSA – 77%

The heat protection of automotive window films is primarily not a question of energetics, but an issue of decreasing transmitted heat. For this reason, it is better to use TST than TSER, as it shows the technological difference between window films series.

Many in the market use the Infrared Rejection (IRR) parameter as well. The energy content of the radiation that falls on the glass surface is made up of visible light (in about 47%) and infrared radiation (about 53%). When the IRR value is used in comparisons, we have to assume that the visible light transmission of the two films is the same, or else comparing the values is not sensible. It is a further problem that a lot of people cheat with IRR by providing it for a certain range only, so in order to understand this value, it is indispensable to know the whole transmission curve.

The second large group of parameters is the ones related to visible light. The Visible Light Transmitted value shows how light the window film is, while the Visible Light Reflected parameter indicates the reflective characteristic of the surface. In Hungary, automotive window films with more than 10% reflectivity will not be certified.

Within the group of other parameters, UV rejection is important to mention.

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