Visible Light Transmitted (VLT), Infrared Rejected (IRR), Total Solar Energy Rejected (TSER), Visible Light Reflected (VLR)…
Feb 28 2023 Sophia
What do all these terms mean?
When looking for window films for your home, you may have stumbled across terms like VLT, TSER, VLR, IRR etc. These terms can be daunting for a first-time buyer; “What do these terms mean?”, “What terms must I pay special attention to?”
We’ve got you covered! Let’s take a closer look at each term and break down their meaning and significance.
We will be using the table below as a reference:
What is Solar Energy?
Before we start dissecting the meaning of each term, it is important to understand what solar energy is made up of.
Solar energy from the sun is made up of 3 components; Visible Light (VL) which we can see, Infrared Rays (IR) which we feel as heat, and Ultraviolet (UV) rays which are invisible. Sunlight at Earth’s surface is around 53% IR, 43% VL, and 4% UV.
So the term Total Solar Energy (TSE) simply refers to the sum of these three radiations:
Total Solar Energy (TSE) = Visible Light (VL) + Infrared Rays (IR) + Ultraviolet (UV) rays
A high-quality solar film aims to effectively regulate the levels of all three radiations, while still maintaining a balance – We wouldn’t want a cool but dark looking house because all visible light has been blocked out, would we?
What is Visible Light Transmitted (VLT)?
Visible Light Transmitted (VLT) is the amount of Visible Light (VL) that passes through the glass. The higher the percentage of VLT, the greater the amount of light that passes through the glass. To block out glare, you will want to select a film that has a lower VLT (i.e., the darker looking film).
Let’s take a look at the table below:
From the table, you can see there are 5 percentages of VLT – 21%, 40%, 51%, 61%, and 69% – for this specific series of window film. It simply means that PR20 allows only 21% of light to pass through, while PR70 allows much more light – almost 70% – through. Not surprising, PR20 is a much darker film than PR70, since excessive VL (i.e. glare) can only be countered by a darker film.
Apart from glare, VL can also contribute to the heat (since it makes up 43% of the TSE). A simple way to understand the relationship between heat and light is: more light = more heat. If you were to compare two films with exactly the same film technology, the darker film will reject heat more effectively than the lighter film.
It might get a little confusing here. Even though a darker film is more effective in blocking out heat than a lighter film, you might be thinking “As long as my window film is dark, I can block out all the heat, right?” Wrong. This is not true as in reality, heat is caused largely by IR (which makes up 53% of the TSE – remember the pie chart above?), which cannot be block out just by using a dark film but by the film’s technology.
What is Infrared Rays (IR) Rejected?
Infrared Rays Rejected (IRR) is the total amount of infrared heat (IR) that is blocked out by the window film. The higher this number, the more IR is being rejected. Since IR is the main source of heat (53% of TSE), a higher IRR means that more heat is being blocked out.
Here, this series of window film is able to block out 97% of IRR. However, keep in consideration that this is true only for IR with wavelength of 900nm to 1000nm. In actuality, IR is measured over the wavelength from 780nm to 2500nm. Hence, you might want to ask the window film company for their film’s complete wavelength of IR Rejection.
Oftentimes, people use IRR to determine the level of heat rejection. However, this is not an accurate guide as IRR only covers a fraction of TSER. Hence, when you want to compare how much heat two films can reject, it is best to compare their TSER values as well (we will cover this in depth below).
What is UV Rejected?
UV Rejected is the total amount of UV that is blocked out by the window film. The higher this number, the less UV rays passes through the window. A good quality window film will reject a minimum 99% of UV rays. This means that apart from blocking out most of the harmful radiation, the film will pretty much block all the heat that is produced by UV as well.
So far, we have dissected the meaning and significance of VLT, IRR, and UV Rejected. But when deciding which window film is best at rejecting heat, the most important term to look out for is TSER.
What is Total Solar Energy Rejected (TSER)?
As mentioned above, TSER is the best indicator of heat rejection performance of a film. This computation takes in account heat from the whole solar spectrum; VL, IR, and UV. The higher the TSER percentage, the more heat is blocked out by the film.
Let’s circle back to this table:
As seen from the table above, PR20 has a TSER of 62%. Simply put, it means that PR20 can reject 62% of the sun’s heat.
But… What is TSER (On 60 Degree Angle) then? This might not be a term you have come across while looking for window films. Most window film companies test their films when the sun is perpendicular to the window (see image below). However, this is not an accurate test since the hottest parts of the day is when the sun is high up. Companies who do testing on their films when the sun is at a 60 Degree Angle obtain much more accurate results on the effectiveness of their films to block out heat.
In essence, window film companies oftentimes make statements such as “rejects up to 90% of infrared heat” to get your attention. While these claims are technically true, they do not paint the whole picture of what consumers should be looking out for when getting window films. So do not be tricked!
By now, you should know to be looking out for and comparing TSER values and not just IRR values – I hope so! This way, you can be rest-assured of the amount of heat-rejection you are truly getting.
Now that you know all the technical terms that window film companies use, you are on your way to being able to compare the different films in the market. Some other questions you might want to ask yourself to give you a better guide include:
- What problems am I facing in my home/office – heat/glare/fading of furniture/privacy?
- How much visible light do I want entering my home/office?
If you are not convinced of the heat-reduction properties of a window film, you should book an appointment with the company to do a demo test of the film onsite. This way, you will be able to experience first-hand the effectiveness of these films.
Got any questions about solar films that haven’t been answered here? Feel free to contact us. We’re happy to help home owners in their home solutions journey.
At Jestac, we distribute world-class 3M Solar Films for customers across Singapore. If you are shopping around for window films and other interior solutions, feel free to take a look at our prestige solar films, visit our blog, or request custom pricing using the button below.
Book an appointment with us!
If you would like an accurate price, we offer free on-site consultation, with no obligation charge. Our window film specialist will assist and advice you on which type of window film is suitable for you with respect to your requirements. After consultation, we will provide a final price to you.
How to contact us?
Check out what our customers have to say about us here.