4 ms·
In the US the rating associated with this loss is called Visible Light Transmission, or VLT, and it can be quite low by percentage, especially in ‘Low-E’ window
by doctorhandshake 4y ago
In the US the rating associated with this loss is called Visible Light Transmission, or VLT, and it can be quite low by percentage, especially in ‘Low-E’ windows designed for sunny climates. The nature of our perception of light intensity means that the use of a percentage of transmission might not be the best measure for the effect. I feel like something like the geometric scale of the f-numbers used in cameras would be more appropriate for how the change in light intensity feels, which I think is the intent of the VLT factor as there is also a Solar Heat Gain Coefficient (SHGC) that relates to the performance of the window in that regard.
- hgomersall 4y agoLow-e windows are not just for sunny climes - it's arguably the dominant benefit of modern windows. Interestingly, when you put low emissivity layers on each pane, it doesn't matter whether it's pointing towards the inside or the outside. When pointing outwards, it reduces the propensity to radiate outwards, when on the inside it reduces the propensity to be heated by radiation. More layers are good because that increases the number of low-e layers you have - with double glazing, you only have two on the insides; with triple glazing you have 4.
- doctorhandshake 4y agoI don’t think you can generalize quite that much - on buildings in heating-dominated climates, low-e windows and their accompanying low SHGC result in rejected solar energy that could otherwise be used to heat the home by day. Without proper shading, overheating can be a concern in fall and spring for south and west facing windows but in my understanding north facing glazing shouldn’t be low-e in any heating dominated climate.