Double-Glazing Questions: What Is Visible Light Transmittance?

Double-Glazing Questions: What Is Visible Light Transmittance?

23 April 2020
 Categories: , Blog

Choosing the right double-glazed windows isn't just a question of choosing a style you like. Window frames and their glass have various ratings that affect their performance and the way they work in your home.

For example, double-glazing glass comes with a visible light transmittance rating. What does this rating mean, and how does it affect your glazing choice?

What Is Visible Light Transmittance?

Visible light transmittance refers to the glass's ability to allow light in through a window. While you may think that all glass lets in the same amount of light, this isn't the case.

Treatments and coatings affect this visibility. For example, if you install a glass that has a solar protective coating, then this coating might reduce light transmittance into a room.

Here, the coating deflects or cuts out some solar rays as they hit the window. However, in doing so, it creates a barrier on the glass that affects the light that can come through the glass. So, in this case, a window might let in less light than an untreated one would.

Why Is Visible Light Transmittance Important?

The visible light transmittance rating on glass affect the light that comes in your home. Get this right, and you get the right amount of light.

However, if you choose glass with the wrong rating, then some of your rooms might be too dark. Or, you may have too much light coming in, which creates over-hot rooms and too much glare.

What's the Right Visible Light Transmittance Rating for Your Home?

This kind of light is measured as a VLT (visible light transmittance) or TvW (visible transmittance of the window) number. The lower the VLT or TvW number a glass has, the less light it lets in; higher ratings bring in more light.

It's important to look at your rooms and their windows before you decide on a rating. For example, if you are installing a window in a small dark room, then you want a higher rating. This brings as much light as possible inside.

Alternatively, if you have a large and airy room with lots of big windows, then it might be better to go for a lower rating number. You might prefer to control incoming light to make sure that the room isn't overly bright and hot.

Bear in mind that this might mean choosing different ratings for different areas of your home. To learn more and to get advice on good ratings, talk to your double-glazed windows supplier.

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