Everything You Need to Know About Visible Transmittance

There’s a lot that goes into rating windows and deciding whether or not they’re energy efficient. You need energy efficient windows on your home to save money and stay comfortable year round. Although it’s not so much geared towards saving energy as other ratings, visible transmittance is one of the important properties that goes into rating windows.

visible transmittance

Installing new windows or replacing old ones is a big investment for any homeowner. It’s extremely important that you get the right windows for your home so you don’t end up spending money on fixing issues because you made a fast decision without any real research.

What is visible transmittance? How is it measured? Why is it important? We’ll go over all the questions you may have about visible transmittance to help you get the best windows for your home.

What Is Visible Transmittance?


Also known as VT, visible transmittance is the measure of how much visible light travels through the window into your home.

The National Fenestration Rating Council (NFRC) is the party responsible for rating windows’ visible transmittance.

It doesn’t rate the window’s ability to keep heat in, out or anything real scientific. It’s simply how much natural light will be able to pass into your home.

Don’t let that make you feel like visible transmittance isn’t as important as the other ratings such as solar heat gain and u-factor.

The main reason anything has windows on it is to let in sunlight. Visible transmittance will let you know how much light you’ll be getting.

Something that happens all the time is when a homeowner gets new windows installed and yet it feels like the room is darker. That could be all from the VT and if they knew what it was beforehand, they could’ve avoided the problem.

What Goes Into Rating Visible Transmittance?

visible light transmittance

You may be thinking, what else besides the glass could possibly tell you how much visible light passes through a window? There are actually a number of different factors that go into rating a window’s VT.

Visible transmittance is a whole-window rating and takes every component into consideration from the frame to the glass.

In terms of numbers and range, VT is measured on a scale of 0-1 with 0 being the lowest amount of light passing through and 1 being the highest amount.

Obviously, the glass is the main contributor to a window’s VT. However, there are other factors such as the frame, sash and grids. If the window has a thick frame or any grids, that will decrease its visible transmittance.

Other factors such as solar heat gain coefficient, low-e coatings and tints all effect a window’s ability to let in visible light. The amount of panes the window has can also effect VT. Triple pane windows usually have a lesser VT because the light has to pass through three separate panes of glass.

Why Is Visible Transmittance Important?

visible transmittance

VT is an important window energy rating because it goes hand in hand with other ratings. For example, you might find a window with very high visible transmittance but that may be at the expense of a higher solar heat gain coefficient.

In such a case, your windows would be letting in a lot of light but also a lot of harmful rays that will heat up your home and cause furniture to fade. This scenario will cause you to lose money on energy bills from having to crank the air conditioning in the summer.

In other cases, you may want a low visible transmittance. If you’re looking to get more privacy, you’ll want to find a window that has lower VT. This can be achieved through tints, glass treatments, grids and frame thickness.

Visible transmittance can also help you save money. If your windows can let in more natural light, you won’t have to rely so heavily on artificial light to brighten up your home. You’ll be able to have the lights off for a longer time when your window’s VT is higher.

With the advances that have been made in window technology, you can now get the best of both worlds in terms of visibility and energy efficiency.

Through low-e and argon gas, you can have a high visible transmittance but your windows will still be able to block out harmful rays and keep your home comfortable.

Don’t Forget About Visible Transmittance

On your search for replacement windows, remember to keep in mind all the ratings that go into deeming a window energy efficient. That means keeping an eye out for visible transmittance too.

If you want more or less sunlight in a room, VT will let you know how much a window will let through.

You’ll want to find a window company that gives you many options so that you can create the best windows for your home. Feldco does just that.

Our windows are the most energy efficient on the market. We weren’t named America’s #1 window company for no reason.

We have many customization options to let you craft the perfect windows. You can choose the type of glass and grid options to allow for different amounts of visible light. Plus, we have many different window styles from double hung to architectural.

Join the over 400,000 homeowners who have trusted us with their home improvement projects and get a free quote for the best windows in the Midwest right now.

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