Glossary

Air permeability
The unintended leakage of air through gaps and cracks in the external envelope of a building. In shading terms this is the openness of the fabric or the perimeter gaps at the edge of the shading.

Conduction
The transfer of heat between substances that are in direct contact with each other.

Convection
The transfer of the heat in fluid or air, caused by the movement of the heated air or fluid itself. In a building warm air rises and cold air settles to create a convection loop and is termed free convection.

Glare
The condition of vision in which there is discomfort or a reduction in the ability to see significant objects, due to an unsuitable distribution of or range of luminance.

Lux
The measure of illuminance on a surface (1 lux = 1 lumen/m2).

Natural Ventilation
The supply of adequate fresh air to space within a home through windows, trickle vents etc.

Radiation
The emission or transfer of energy in the form of electromagnetic waves or particles transferring energy from a warm body to a cold body without heating the air in between.

Solar Gain
The solar radiation that enters the building through glazing hits objects and is converted to heat. This reduces the need to artificially heat the space.

As Solar Absorptance
The measure of the fraction of solar energy absorbed by a fabric or material. A high value means that the fabric absorbs a lot of energy.

g-value
The measure of the total energy passing through the glazing when exposed to solar radiation.

gtot
The measure of the total energy transmittance of the glazing in combination with the blind or other shading when exposed to solar radiation. Also known as the Solar Factor.

Nm Nanometers
A unit of one billionth of a metre, which is used to measure the wavelength of the light emitted by the sun.

Of Openness Coefficient
The ratio between the area of openings in the fabric/material and its total area.

Rs Solar Reflectance
The measure of the fraction of solar energy reflected by the fabric. A high value means that the fabric performs well at reflecting solar energy.

Qi
It results from heat transfer by convection and longwave infra-red radiation of that part of the incident solar radiation which has been absorbed by the glazing. It is the absorbed heat that will not go back through the glass. So it is the part of the absorbed radiation that flows inwards through the combined glazing and shading device.

Suv Outside Shading UV Class
Rating system for the effect of awning fabrics to control UV for those beneath them.

Ts Solar Transmittance
The measure of the fraction of the solar energy transmitted through the fabric. A low value means that the fabric performs well at reducing solar energy transmission. Ts + Rs + As = 100%.

Tv Light Transmittance
The proportion of visible light transmitted through the shading material.

Tv n-dif Diffuse Normal Transmission
The diffused part of the light transmission that scatters in all directions when it hits an object.

Tv dif-h Diffuse Hemispherical Transmission
Classifies the daylight utilisation in a room. It is the ratio of the total transmitted flux to the ideally diffuse incident flux. Ideally diffuse irradiation means that the radiance or the luminance is equal for the whole hemisphere of the incident radiation.

Tv n-n Direct light transmission
The direct part of the light transmittance that goes straight through the openings in a shading material.

Tvis
The fraction of the visible light transmitted into the room.

Utot
The transfer of heat from inside to out through the combination of glazing and shading device.

U-value
A measure of thermal conductance which is the ability of a material to transfer heat.

UV transmittance
The proportion of UV-light transmitted through the shading material.