Glossary of Terminology

ANNEALED GLASS – During manufacture of Float Glass the hot glass is cooled in the annealing lehr removing internal stresses from the raw glass during this process, and refers to the final state of the glass enabling it for good and easy cutting.

COATED GLASS – Thin layers of material are applied to the surface of the glass to add properties to the glass including reduced light transmission, increased solar energy elimination, colour and aesthetic properties. Examples of coated glass include mirror, spectrally selective glass and screened glass.

DOUBLE GLAZING – Two separate panes of glass are separated by an aluminium spacer between them to provide noise and/or thermal insulation of the glazing installation.

FLOAT GLASS – The foremost method of manufacturing normal glass by the Float Glass method. Molten Glass is conveyed onto a bed of molten tin, on which the glass floats. The glass cools to a solid state as it passes over the tin and is then lifted off the tin and onto rollers.

INSULATING GLASS UNITS – Two or more pieces of glass separated by a spacer. The airspace between the two glasses is critical to the insulation value of the unit. The units are designed for thermal insulation, but have the welcome advantage of reduced noise transmission and lower solar energy transmission.

INTERLAYER – The plastic layer between two pieces of glass which is used to make laminated glass. CITY GLASS always uses Polyvinyl Butyral – (PVB) for this purpose. The interlayer imparts additional properties to the glass including safety, security, solar control, light control, UV control, colour and sound absorption.

LAMINATED GLASS – Two or more pieces of Float Glass joined together by the PVB interlayer and subjected to heat and pressure. The Lamination process combines the properties of the glass with the properties of the interlayer. CITY GLASS Laminated Glass that is correctly marked – is a safety glass. However, unmarked glass or some other brands of laminated do not qualify as a safety glass.

NORMAL GLASS – Normal glass for buildings is the basic glass with which most buildings are glazed. It forms the basis from which all other glass is derived. It is a clear glass with a uniform appearance appreciated for its smooth flat surfaces.

SHADING CO-EFFICIENT – The ratio of Total Solar Energy transmission of a glass compared with the Total Solar Energy transmission for ordinary 3mm float glass. The lower the shading co-efficient number, the lower the amount of solar heat transmitted. This is dependent upon environmental conditions.

SOLAR ENERGY – All energy received from the sun on the surface of the earth. This includes the energy from the Ultra Violet, Visible and Infrared segments of the Solar Spectrum. For reasons of standardisation solar energy is measured between the wavelengths 280nm (nanometers) and 2500nm.

SOLAR ENERGY ABSORPTION – The part of the sun’s energy which is absorbed by the glass. This energy causes the glass to warm up.

SOLAR ENERGY DIRECT TRANSMISSION – The part of the sun’s energy which passes through the glass. This is independent of environmental conditions.

SOLAR ENERGY REFLECTION – The part of the sun’s energy which is reflected by the glass or glazing system. This is independent of environmental conditions.

SOLAR ENERGY TOTAL ELIMINATION – The part of the sun’s energy stopped by the glass or glazing system. This value will change when subjected to varying environmental conditions. In warm climates, glazing systems are compared using the American Society for Heating, Refrigeration and Air-conditioning Engineers (ASHRAE) Summer day time conditions. The environmental conditions, which affect Solar Heat Elimination, include air speed against both surfaces of the glass and temperature also on both surfaces of the glass.

SOLAR ENERGY TOTAL TRANSMISSION – Added to the Solar Energy Direct Transmission is the energy that is radiated into the building from warm glass. This is dependent on environmental conditions.

SPECTRALLY SELECTIVE GLASS – Glass which is designed to allow as much visible light through as possible but as little solar heat as possible. As solar energy is also carried in the visible light part of the solar spectrum, higher solar energy elimination than 50% can only be achieved by sacrificing significant quantities of light.

STRENGTH – Referring to Laminated glass, the strength is defined by the performance of the Polyvinyl Butyral interlayer (PVB).
0.38mm thickness of PVB interlayer is Normal Strength – (NS)
0.76mm thickness of PVB interlayer is High Penetration Resistance – (HPR)
1.52mm thickness of PVB interlayer is High Impact – (H)

THICKNESS – The thickness of ordinary float and rolled glass is normally described as the nearest whole number within the thickness variation. Each glass has a nominal thickness of 3mm, 4mm, 5mm or 6mm. A standard Polyvinyl Butyral (PVB) has a thickness of 0.38mm, but also available is 0.76mm, 1.14mm and 1.52mm. The thickness of a laminate made of two 3mm glasses with a 0.38mm PVB interlayer is
therefore 6.38mm – (NS). Also the thickness of a laminate made of two 3mm glasses with a 0.76mm PVB interlayer is described as 6.76mm – (HPR). (see above “Strength”)

TINTED GLASS – Glass which has had a colour either incorporated into the glass body itself, or introduced by a tinted PVB interlayer of a laminated glass.

TOUGHENED GLASS – Toughened Glass is manufactured by subjecting annealed glass to a process of controlled heating and rapid cooling. The process sets up high compressive stress at the surface of the glass with balancing tensile stress in the centre of the glass.
Toughened glass is at least five times stronger than conventional annealed glass. Once thermally toughened, the glass will fragment into hundreds of harmless small pieces if broken, cut or drilled.

U-VALUE – A measure of heat entering a building through the glass by conduction. The lower the U-Value is, the better the insulation and the more effective the control of heat loss or gain. The U-Value is dependent on environmental conditions.

VISIBLE LIGHT – Visible light is the part of the energy generated by the sun, which reaches the surface of the earth and is visible to the average human eye. Technically speaking, this is a spectrum of electromagnetic radiation at wavelengths of between 380nm and 780nm.

VISIBLE LIGHT REFLECTION – The percentage of visible light reflected from the surface of the glass, when the sun shines at right angles to the surface of the glass. The reflection increases as the angle of the sun decreases.

VISIBLE LIGHT TRANSMISSION – The percentage of visible light transmitted through the glass when the sun shines at right angles to the surface of the glass.