--- title: Common Measurements Used to Rate Window Films and Coatings description: Common Measurements Used to Rate Window Films and Coatings image: https://stcloudwindow.com/hubfs/Imported_Blog_Media/thumbnail-of-windows-in-the-sun-1.png --- # Common Measurements Used to Rate Window Films and Coatings **Written by: St. Cloud Window** **Date: February 5, 2026** With the huge variety of window films and coats available, knowing which are ideal for your needs can take time. Even harder can be deciphering what measurements mean and which ones are relevant. ![windows in the sun](https://stcloudwindow.com/hs-fs/hubfs/Imported_Blog_Media/To-Boone-Pickens-Conference-Hall-1-300x225-2.jpg?width=600&height=450&name=To-Boone-Pickens-Conference-Hall-1-300x225-2.jpg) [FacilitiesNet](https://www.facilitiesnet.com/windowsexteriorwalls/article/3-Windows-Numbers-To-Know--16790) breaks down the most common measurements used to rate window films and coatings: The** visual transmittance (VT) value** indicates how much visible light passes through the film or coating. With a maximum value of 1.0, the higher the VT value, the more visible light is passed. A typical uncoated, dual-glazed window will have a VT of approximately 0.81. The same window with a Low-E coating will have a VT of roughly 0.78. Adding a window film or coating can reduce this to as low as 0.33. At that value, the glass will have a dark appearance. For most applications, a good minimum target value is 0.65. A second measurement is the **solar heat gain coefficient (SHGC)**. This metric ranges between zero and one and rates the solar heat gain through the film or coating. The lower the number, the more effective it is at blocking solar heat gain. A third helpful measurement is the **light-to-solar-gain (LSG) ratio**. The LSG measures the visible light admitted through the film or coating relative to the solar heat gain. A typical dual-glazed window with no coatings has an LSG of 1.06. Adding a Low-E coating changes it to about 1.16. The higher the LSG number, the better the film or coating blocks heat gain while admitting daylight. For more window information, check out our [Choosing the Right High-Efficiency Windows](https://stcloudwindow.com/news/energy-efficient-windows/) and [Quality Materials are Essential to High-Performing Products](https://stcloudwindow.com/news/quality-materials-are-essential-to-high-performing-products/) posts. ## The Latest Window Industry News Blogs, insights, and more. [![Ever wonder why STC ratings for doors are important? ](https://stcloudwindow.com/hubfs/Imported_Blog_Media/Hope-Church-11c-1.jpg) ### Ever wonder why STC ratings for doors are important?  Simply stated noise impacts our health. 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