What does Ug mean, UV or light transmission? Learn how window performance directly impacts your costs and quality of life.
In a context where the energy efficiency of buildings is regulated more and more strictly and required in quality projects, the correct choice of thermal insulating glass is no longer an aesthetic matter, but an essential technical decision. At Valras, we deliver glazed solutions that meet the most demanding energy performance criteria.
In this article we explain what the Ug coefficient means, the differences between UV, solar and light transmission, and how these characteristics influence the comfort, efficiency and, most importantly, the energy costs of a building.
What is the Ug coefficient and why is it essential?
The coefficient Ug (U-glass) is the most important indicator of the thermal insulation of the glass. It measures the ability of the glass to transfer heat. The rule is simple: the lower the Ug value, the lower the heat loss, which directly leads to lower energy consumption.
How to measure:
- It is expressed in W/m²K (watts per square meter per degree Kelvin).
- It is tested in accredited laboratories, under standardized conditions (according to European norm EN 673).
- Usual values for modern insulating glass are between 0.5 and 1.3 W/m²K.
Recommended values:
- Below 1.0 W/m²K: Required for passive houses and high energy efficiency buildings (nZEB).
- 1.1 – 1.3 W/m²K: Good standard for new commercial or residential buildings.
- 1.4 – 1.6 W/m²K: Acceptable for buildings in mild climate areas.
IMPORTANT! VALRAS has glazing with Ug=0.5 W/mpK in series production
Attention: Do not confuse Ug with Uw or Uf!
The actual performance of your window depends on the whole assembly, not just the glass.
Uw (U-window): It represents the heat transfer coefficient of the entire window (glass + profile). This is the final value that counts in the calculation energy of a building.
Uf (U-frame): It measures the heat loss through the window frame/profile. Usually, the profile has a higher U-value (insulates less) than glass.
Concrete example: Even if you choose an excellent window (Ug = 0.6 W/m²K), if the profile is weak (Uf = 1.2 W/m²K), the final value of the window (Uw) will be somewhere around 0.9 – 1.1 W/m²K. That's why the collaboration between the glass supplier and the carpentry is crucial.
Light vs. Heat: The Difference Between UV, Solar and Light Transmission
Energy efficiency does not only mean insulation, but also intelligent management of solar radiation.
UV (ultraviolet) transmission: Expresses the percentage of UV radiation that passes through the glass. These rays are the main culprit for discolouration of furniture, parquet and textiles. Valras performance windows, especially laminated ones, block over 99% of UV.
Total Solar Transmission ("g" Factor or SHGC): Represents the total percentage of solar energy that penetrates the interior, heating the room. A small "g" factor is ideal in summer or for south-facing facades, as it prevents overheating.
Light Transmission (LT or TV): Indicates the percentage of visible light that passes through the glass. A high LT means brighter and more pleasant interior spaces, reducing the need for artificial lighting.
The perfect balance is a high LT (lots of light) and an optimized "g" factor (heat control).
Types of performance glass and how we combine them
At Valras, we achieve top performance by strategically combining different types of glass:
Low-E glass (low emissivity): It has an invisible metal layer that reflects heat back inside in winter. It is essential for a low Ug.
Glass with Solar Control: It reflects a significant part of the solar energy, being ideal for offices, glazed facades and areas exposed to the sun.
Laminated Glass: Composed of two sheets of glass bonded with a PVB film, it offers superior impact safety, excellent sound insulation and the best UV protection.
By combining these technologies (eg: a triple pane with Low-E glass + laminated glass + argon gas), we obtain a product that simultaneously optimizes thermal insulation, visual comfort, safety and interior protection.
Certified quality, cutting-edge technology
Choosing the right partner for glazing solutions is as important as the technical specifications of the product. At Valras, we combine technical expertise with modern manufacturing capability to deliver excellence on an industrial scale.
Our production of thermal insulating glass is based on state-of-the-art fully automated lines that ensure millimeter precision and constant quality, regardless of the complexity of the order. Each glass unit is manufactured following the strictest procedures and undergoes rigorous quality control.
Our quality is not just a promise, but a certainty validated by certifications according to European standards (EN 1279, EN 410, EN 673). This commitment allows us to offer reliable and durable solutions adapted to any type of project and use – from windows for individual homes, to residential complexes, office buildings or large commercial facades.
Choose Valras for a partner that transforms architectural glass into performance solutions, delivering quality, efficiency and safety for your project.
Are you ready to invest in comfort and efficiency? Contact us for a personalized offer!