If you plan to replace your windows, you may have stumbled upon something called window Visible Transmittance (VT), and now you’re wondering what it means and whether it’s an important metric, right?
In short, window Visible Transmittance measures how much visible light passes through a window. As such, understanding VT is crucial if you want to boost the amount of natural light in your home. This article will tell you everything you need to know about VT, so read on!
Key Takeaways
- Visible transmittance (VT) measures how much visible light passes through a window. It is measured from 0 to 1; the higher the VT of a window, the more natural light passes through it.
- High-performance windows, guided by NFRC ratings, balance VT with considerations like the Solar Heat Gain Coefficient (SHGC). For a perfect balance between SHGC and VT, homeowners should pay attention to the Light-to-Solar Gain (LSG) ratio.
- Factors affecting VT include the number of glass panes and coatings, frame thickness, and the insect screen type.
What Is Window Visible Transmittance?
Window Visible Transmittance (VT), also known as visual transmittance, refers to the amount of visible light that passes through a window. It is measured on a scale from 0 to 1. This scale quantifies how well windows transmit natural light. Higher numbers mean that more visible light is transmitted through the window. As such, if the VT of a window is 0.6, that window will allow 60% of sunlight in. If the VT is 0.2, the window will allow only 20% of sunlight in.
A good VT rating not only reduces the need for artificial lighting but also enhances the overall ambiance of your home by making it feel brighter and more welcoming.
What Is Light-to-Solar Gain?
If you’re wondering what VT is, you may have also stumbled upon the Light-to-Solar Gain (LSG) coefficient. It is basically the ratio between the Visible Transmittance and the Solar Heat Gain Coefficient (SHGC). While VT measures how much light enters your home through the window, the SHGC measures how much solar heat passes through it. As such, the higher the LSG, the more light passes through the window without letting in excessive amounts of heat and radiation.
How Is Visible Transmittance Measured?
VT, also known as visible light transmittance, is gauged by the volume of visible light that can penetrate a glass unit. This measurement plays a key role in ascertaining the quantity of natural light that can enter a space. The measurement process involves assessing the fraction of the sunlight spectrum visible to the human eye.
According toEnergy.gov, VT “is a fraction of the visible spectrum of sunlight (380 to 720 nanometers), weighted by the sensitivity of the human eye, that is transmitted through the glazing of a window, door, or skylight.”
While the Visible Transmittance is not required for Energy Star certifications, it is included in the National Fenestration Rating Council (NFRC) label, so any windows that have been tested for it should have a VT rating. The NFRC label provides a comprehensive way to compare a window’s energy properties, helping homeowners make informed decisions.
If you want to check the Visible Transmittance of Magic products, click here.
What Is a Good Visible Transmittance for Windows?
The higher the Visible Transmittance rating, the better; therefore, the closer the VT is to 1, the more natural light the room will get.
The truth is that no glass is completely translucent, even if it looks so. Therefore, you’ll likely never find a window with a VT of 1. Therefore, you should aim for windows with a VT as close to 1 as possible. At the same time, don’t forget to consider where the window is located. For example, if it gets plenty of sunlight during the day, you may want to look for a lower VT so the room isn’t too bright. Conversely, if the window isn’t always sun-kissed, you’ll want the highest VT possible to enjoy natural sunlight for most of the day.
In addition, don’t forget about other energy performance ratings. We’ll discuss them further down below. But first, let’s see what influences the VT rating.
Factors That Influence Visible Transmittance
The factors that influence a window’s visible transmittance (VT) include glass type and coatings, window frame designs, and insect screens. These elements play a crucial role in determining how much visible light passes through the window and enters your home. Let’s discuss a bit about each.
Glass Type and Low-E Coatings
The type and thickness of the glass used in windows significantly impact VT. The same is valid for Low-E coatings, which are ultra-thin coatings added to the glass that help regulate the passage of solar radiation, including ultraviolet and infrared light. If a window has two or three glass panes, you can add several Low-E coatings. Although they’re almost transparent, they can still lower the VT rating.
Here’s how the VT ratings vary across Magic products depending on how many glass panes and coatings they have:
- Double-pane casement window with 1 Low-E coating: VT – 0.53; SHGC – 0.48; U-factor – 0.33
- Double-pane casement window with 2 Low-E coatings: VT – 0.42; SHGC – 0.18; U-factor – 0.24
- Triple-pane casement window with 2 Low-E coatings: VT – 0.36; SHGC – 0.23; U-factor – 0.17
- Triple-pane casement window with 2 Low-E coatings: VT – 0.47; SHGC – 0.39; U-factor – 0.20
As you can see, a window with more glass panes and Low-E coatings has a lower VT. However, the last line shows that some Magic triple-pane windows have three glass panes, two Low-E coatings, and still quite a high VT. How’s it possible? Easy! Because we manufacture our own glass units. This allows us to customize everything – from gas fills to coatings. Therefore, our products will suit your preferences, climate, and home construction. That’s why some of our products have a high VT even if they’re equipped with several Low-E coatings. This way, you can have both highly energy-efficient windows and plenty of natural light!
Another thing you may have noticed is that higher VT ratings equal higher SHGC ratings. While a high SHGC is excellent for homes in Northern Canada, you’ll want less solar heat gain if your home is exposed to sunshine year-round. So, how can you balance all these? With Magic’s help, of course!
Frame Design
The design of the window frame also plays a critical role in determining how much light enters a home. Obviously, if the frame is thick, it will cut from the glazing area. This may not be a problem for large windows. Smaller ones, on the other hand, may have their glazing area cut in half with thick frames.
That’s why you should go for frames that are slim and strong – Magic’s Hybrid Fusion Frame, for example. Our technology combines vinyl, aluminum, and steel to create the most durable window frames on the market. The strength of our unique material allows us to manufacture the thinnest frames you’ll find in Ontario, thereby increasing VT and contributing to a brighter living space.
Insect Screens
Most insect screens are fixed within the sash. That’s why they cut a window’s VT by 50%. It is worth considering that the product you’re buying likely was NOT tested with the insect screen. Therefore, the numbers you’re seeing on their label do not fully correspond to what you’ll actually get.
This is one of the reasons Magic created fully retractable screens that feature our patented Slide ‘N’ Hide® technology. You can use the insect screen when the window is open and hide it when it’s closed. This way, Magic screens do not affect the window’s VT. In addition, you can also install our solar shades and thermal blinds, which lower the U-factor and improve your windows’ solar heat gain resistance.
Other Energy Efficiency Ratings to Consider
Besides VT, you should also pay attention to the Solar Heat Gain Coefficient, U-factor, and Air Leakage.
Let’s say you’re looking for a large window to maximize daylight in your room. You find the perfect window, install it, and notice that your furniture material begins to fade. This may be a sign that your window has a high Solar Heat Gain Coefficient. While it allows plenty of light in, it also cannot resist the heat gain. That’s why homeowners shouldn’t pick windows solely based on their VT rating. As such, here are other NFRC energy performance ratings to consider:
- Solar Heat Gain Coefficient (SHGC): the window’s ability to resist heat gain; it is measured from 0 to 1; the number you’re looking for depends on the climate.
- U-factor: the window’s ability to resist non-solar heat loss; it is measured from 0.20 to 1.20; you want to look for windows with a lower U-factor.
- Air Leakage (AL): measures how much air passes through a window; it is measured up to 0.3; the lower the AL, the better.
- Condensation Resistance: measures how resistant a window is to condensation; it is measured from 1 to 100; the higher the number, the better.
The NFRC label is a valuable tool for comparing the energy performance of windows, doors, and skylights. High-performance windows not only regulate the flow of heat and light but also contribute to lower energy costs by keeping indoor temperatures consistent year-round and minimizing air leakage.
The Health Benefits of More Natural Light
Exposure to natural light – even if indoors – offers a plethora of health benefits:
- Sun rays can elevate mood by prompting the production of serotonin, a hormone that reduces tension and enhances feelings of happiness.
- Natural light helps regulate circadian rhythms, improving sleep quality and reducing daytime fatigue.
- Natural light can boost your immune system.
- The sun rays in your room can reduce anxiety and the likelihood of developing Seasonal Affective Disorder (SAD) caused by a lack of sunlight.
- Natural light will maintain the room bacteria-free and promote plant growth. This will have positive effects on your body and indoor air quality.
- Having plenty of light in your room can reduce eye strain caused by artificial lighting.
- Working in a room with plenty of natural light can significantly boost productivity.
Contact Magic for Fully Personalized Windows
Without a doubt, understanding window Visible Transmittance (VT) is essential for optimizing natural light in your home. However, choosing windows that balance VT, SHGC, and U-value can be quite challenging. Luckily, Magic comes to your rescue! Reach out today for a free consultation and get fully personalized windows tailored to your needs, home design, and climate!
Frequently Asked Questions
What is window Visible Transmittance (VT)?
Window Visible Transmittance (VT) measures the amount of visible light that passes through a glass window, with higher values indicating more light transmission. It’s expressed on a scale from 0 to 1.
How is VT measured?
A window’s VT is measured as a percentage of visible light passing through a glass unit, determined by the fraction of sunlight spectrum visible to the human eye.
What factors influence VT ratings?
VT ratings are influenced by how many glass panes and Low-E coatings the windows have, the thickness of the frame, and the insect screen type.
How can I balance VT with energy efficiency?
To balance VT with energy efficiency, consider the solar heat gain coefficient (SHGC), which should be low, especially in regions with a warm climate. You should also consider the light-to-solar gain (LSG) rating – a ratio between VT and SHGC. The higher the LSG, the better.
What are the health benefits of increased natural light?
Increased natural light exposure has numerous health benefits, including improved mood and sleep quality, increased energy levels, and reduced anxiety.