The percentage of visible light that passes through glazing materials, affecting interior brightness and visual comfort in buildings.

Visible Light Transmission is the percentage of visible light that passes through glazing materials, affecting interior brightness and visual comfort in buildings through optical properties that determine how much natural daylight enters interior spaces while influencing energy performance and occupant satisfaction. This fundamental glazing characteristic measures the fraction of visible spectrum light (380-780 nanometers) that transmits through glass or other transparent materials, expressed as a percentage that directly impacts interior illumination, visual connection to outdoors, and overall building performance. Visible light transmission is a critical consideration in fenestration design where it affects daylighting strategies, energy efficiency, occupant comfort, and architectural aesthetics, making it essential for window selection, building design, and any application where balancing natural light admission with energy performance and visual comfort is necessary for optimal building function.

Visible light transmission is evaluated in various glazing applications and building contexts including residential windows where it affects interior brightness and connection to outdoor views, commercial buildings where it influences daylighting strategies and energy consumption, institutional facilities including schools and hospitals where natural light quality affects occupant well-being and performance, retail environments where it impacts merchandise visibility and customer experience, office buildings where it affects workspace quality and employee productivity, and specialty applications including museums, galleries, and laboratories where precise light control is critical for function and preservation. Each application requires appropriate VLT selection based on orientation, climate, and use requirements.

The measurement and specification of visible light transmission include standardized testing procedures that measure light transmission across the visible spectrum, weighted calculations that account for human eye sensitivity to different wavelengths, whole-window VLT values that consider frame effects and glazing area, center-of-glass measurements that evaluate glazing material properties, and comparative ratings that enable product selection and performance comparison. Understanding measurement methods enables accurate specification and realistic performance expectations.

Fun Fact: The human eye is most sensitive to green light at 555 nanometers, which is why VLT measurements are weighted to match human visual response, and clear glass typically has a VLT of about 90%.

• Light Gauge Steel
• Light Fixture
• Light Switch