This service provides accurate in-situ measurement of the Visible Light Transmittance (Tvis) of transparent building envelope components such as windows, balcony doors, or innovative glazing systems. The Tvis value is a crucial photometric parameter that quantifies the percentage of visible daylight passing through a transparent element and entering the interior space. It is directly linked to daylighting performance, visual comfort, and energy efficiency, especially in passive and low-energy buildings.
The measurement is carried out under realistic conditions in the NTUA LivingLab, a dedicated research infrastructure designed for building component testing. The LivingLab includes modular window slots that allow easy installation of the customer’s glazing system and provide south-facing exposure to daylight under varying weather conditions.
The Tvis is determined by measuring the ratio of transmitted to incident visible radiation, using calibrated lux sensors (illuminance sensors) placed:
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On the exterior side of the glazing (to capture incident daylight illuminance)
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On the interior side behind the glazing (to capture transmitted illuminance)
The measurements are taken over the course of several days to account for different lighting conditions, ensuring reliable and representative data. By computing the average transmitted illuminance relative to the average incident illuminance on a vertical plane, the Tvis value is derived. This method is particularly valuable for assessing daylighting potential in façade-integrated systems or in the development of new transparent coatings.
The service is suitable for materials and systems in the Technology Readiness Level (TRL) 5 stage or higher, supporting developers in validating claims for light-transmitting performance, or in generating input data for simulation tools and certification processes.
