Glossary

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V

Vapor retarder
A material that reduces the diffusion of water vapor across a building assembly.
Vent
The movable framework or sash in a glazed window that is hinged or pivoted to swing open.
Vinyl
Polyvinyl chloride material, which can be both rigid or flexible, used for window frames.
Vinyl-clad window
A window with exterior wood parts covered with extruded vinyl.
Visible light
The portion of the electromagnetic spectrum that produces light that can be seen. Wavelengths range from 380 to 720 nanometers.
Visible reflectance
The measured amount of energy in the visible wavelength range that is reflected by a window system, expressed as a percentage.
Visible transmittance (VT)
The percentage or fraction of the visible spectrum (380 to 720 nanometers) weighted by the sensitivity of the eye, that is transmitted through the glazing.