GlassCatalogue_LowRes

Glossary Of Terms / U-W
U-value or K-value
This value describes the rate of thermal energy passing through a material due to
conduction, convection and radiation under specific environmental conditions. It is
calculated using material thermal conductance and surface emissivity values which are
intrinsically measured. Lower values describe lower rates of heat energy transmitted
through a material and hence improved insulation values.
Vacuum coated
The process in which, by passing an electric current through an ionized gas and thus
bombarding the surface of a metal cathode with ions, atoms of the desired metal are
vaporised and then deposited in a thin film on the surface of glass. Also known as soft
coats and sputter coated glass.
Vents
Small cracks at the edges of glass that can lead to breakage.
Vinyl back mirror
Mirror with an organic vinyl backing applied that holds the glass together when broken.
Viscosity
The thickness and the stickiness of a substance and how easily it flows. The more viscous a
material, the thicker it is in consistency.
Visible Light Energy
Visible light energy is defined, by international standards, as electromagnetic radiation
energy with wavelengths between 380 and 780 nanometers and is the only type of
radiation visible to the human eye.
Visible Light Transmittance
Visible light transmittance is the term used to describe the fraction of the incident visible
light energy which passes through the glazing material of a window, expressed as a
percentage.
Visible Light Reflectance In
This is the term used to describe the fraction of incident visible light energy reflected from
the exterior surface of the glazing material of a window, expressed as a percentage.
Visible Light Reflectance - Out
This is the term used to describe the fraction of incident visible light energy reflected from
the exterior surface of the glazing material of a window, expressed as a percentage.
Warp
A bump, wave or twist rather than the perfectly level plane of the surface of a sheet of
glass.
Warm edge technology
Term used to describe technology that uses insulated glass spacers to achieve better
thermal performance of an insulated glass unit, particularly evident in the increase of
edge surface temperatures on the indoor side in the winter.
254 Product Catalogue For Glass Processors & IG Manufacturers