Terminology

Categories: Support & Terminology

Absorptance
The proportion of incident solar radiation absorbed by the glass, expressed as a fraction.  See solar properties.

Absorption
An alternative word for absorptance, expressed as a percentage.

Brise Soleil
A partial shading device, usually above a window on the exterior of a building.

Cold radiation
A description of the apparent effect felt when sitting near to a cold window surface, e.g single glazing in cold weather.

Comfort
See thermal comfort.

Diffusing
Randomly scattering the incident light while still allowing transmission.  Usually applied to the effects on light of acid etching, sand blasting and white interlayers.  See also translucent.

Diffusion
See diffusing.

Direct transmittance
The proportion of solar radiation that goes straight through the glass without being absorbed.  See also solar properties.

Electromangnetic attenuation
See electromagnetic shielding.

Electromagnetic radiation
The full spectrum range from gamma rays with very short wavelength, through X-rays, UV light (generally described as 280nm to 380nm wavelength), visible spectrum (generally described as 380nm to 780nm) and infrared, to radio waves with very long wavelength.

Electromagnetic shielding
The use of a Faraday Cage to reduce or prevent the passage o the longer wavelengths of electromagnetic radiation, usually at the frequencies of radar and radio waves.  The electromagnetic attenuation given by the Faraday Cage is measured in decibels.

Emissivity
The ability of a surface to absorb ore emit electro-magnetic radiation.  In terms of glass, emissivity is only important with respect to long wavelength radiation (in the range 5000nm to 50000nm) produced as radiated heat by objects at around room temperature.  Glass naturally has a high emissivity glass (low E glass), the glass surface does not absorb the radiated heat, but reflects it back into the room, enhancing the U-value of the glazing.
 

Glare
Excessive illumination or excessive contrast between lit and unlit areas, which cause difficulty with vision.

Glare reduction
The ability to reduce glare problems, either by reducing the overall illumination or by diffusing direct light or a combination both.

Glazing factors
Another term for radiometric properties, i.e solar properties and optical properties.

Greenhouse effect
The retaining of solar heat by glass, for two reasons.  Firstly, the presence of the glass prevents the wind from removing the heat rapidly.  Secondly, the glass lets through the short wavelength radiation direct from the sun, but is opaque to the long wavelength radiation emitted by the warmed items inside the greenhouse so the heat takes a lot longer to escape than it does to enter the greenhouse, resulting in the greenhouse getting warm inside.  See also effective U-value.

Heat gain
See solar heat gain.

ISO range
The part of electromagnetic radiation, which is UV, light according to the ISO definition (between 280nm and 380nm).

Light diffusion
See diffusing.

Light reflectance
The proportion of the visible spectrum, which is reflected by the glass, expressed as a fraction.  See optical properties.

Light reflection
An alternative term for light reflectance, expressed as a percentage.  Light reflection can be described as low (<15%) or high (>15%).

Light shelf
A reflective device (possibly a partial mirror), placed in a position near the upper edge of a window, which redirects light form the sun and sky on to the ceiling or towards the back of the room, in order to improve the natural illumination within the room.

Light transmittance
The proportion of the visible spectrum, which is transmitted by the glass, expressed as a fraction.  See optical properties.

Light tramsmission
An alternative term for light transmittance, expressed as a percentage.  Light transmission can be described as low (<25%), medium (>25^ and <50%), or high (50%).

Lighting conditions
The level of illumination, specifically the illumination on the public side and the private side in relation to one way vision effects.

Long wavelength energy
An alternative term for long wavelength radiation.

Long wavelength radiation
That part of the electromagnetic spectrum (i.e. from 5000nm to 50000nm wavelength), which is produced by objects at around room temperatures.  Glass is opaque to this radiation so short wave radiation form the sun is trapped by glass, giving the greenhouse effect.  It is possible to design coatings which are transparent to visible light, but which are highly reflective, i.e. have a low emissivity, to long wavelength radiation.  Glass with such a coating is called low E glass.

Long wave shading coefficient
See shading coefficients.

LWSC
Long wave shading coefficient.

Optical properties
The light transmittance and light reflectance or glass products.

Optical quality
The light presence or absence of visual distortion or small blemishes in the glass.

Polarised light
Light waves, which are vibrating in a specific orientation, either after passing through a polarising filter, or after being reflected from a surface or from the sky.

Radiation
Depending on the context it could mean:

• One of the methods of heat transfer across the cavity of an insulating unit, or
• Electromagnetic radiation
• One of the forms in which heat from a fire gets through non-insulating glass.

Radiometric properties

The combined sets of optical properties and solar properties of a glass product.

Reflectance
The proportion of incident light or solar radiation reflected by the glass, expressed as a fraction.  See optical properties and solar properties.

Reflection
An alternative word for reflectance, expressed as a percentage.

Reflective glass
Glass with a coating that reflects light or short wavelength infra-red radiation.

Refraction
The distortion of the path of light as it passes through a glass/air interface.

Relative spectral distribution
A specific description of the solar spectrum used to determine the radiometric properties of glass.

Shading coefficients
The total shading coefficient is a measure of the total amount of heat passing through the glazing (known as the total solar heat transmittance) compared with that through a single clear glass. Glass lets heat through in tow ways; a proportion of the short wavelength radiation is transmitted straight through, while some is absorbed by the glass and re-radiated as long wavelength radiation.  The total shading coefficient is split into two parts relating to the proportions of the total solar heat transmittance which are short wavelength – the long wave shading coefficient.

Short wavelength energy
An alternative term for short wavelength radiation.

Short wavelength radiation
The part of electromagnetic radiation (i.e. from 280nm to 2500nm wavelength), which is radiated by the sun.  The main components of glass are transparent to the majority of this short wave radiation.

Short wave shading coefficient
See shading coefficients

Solar control
The effectiveness of glass in limiting solar heat gain.  Solar control can be described in terms of the total shading coefficient of the glass, as being low (shading coefficient>50%), medium (35%< shading coefficient < 50%), or high (shading coefficient <35%).

Solar direct transmittance
The proportion of incident solar radiation that passes straight through the glass expressed as a fraction.  See solar properties.

Solar energy
An alternative term for solar radiation.

Solar gain factors
Numbers related to and derived from shading coefficient, which also describe the ability of the glazing to reduce solar heat gain.

Solar heat gain
The amount of heat from the sun which passes through the glass into a building.

Solar properties
Those properties of glass related to solar radiation, i.e. reflectance, absorptance, solar heat transmittance, shading coefficients and solar gain factors.  The term is also used occasionally to include emissivities and optical properties.

Solar radiant heat properties
See solar properties.

Solar radiation
The heat, light and UV emitted by the sun as received at the surface of the earth.

Solar spectrum
The electromagnetic radiation emitted by the sun and its variation with the wavelength of the radiation.  The solar spectrum effectively has a range of wavelengths from 280nm to 2500nm, with the largest proportion present as visible light.

Spectral distribution
The proportion of different wavelengths of a spectrum.

Spectrum
The wavelengths contained within a particular type of electromagnetic radiation, such as the solar spectrum.

Thermal comfort
The physical feeling of comfort in relation to the absence of cold radiation and down draughts from window surfaces of insulating units with low U-value..

Total shading coefficient
See shading coefficients.

Total solar energy transmittance
The proportion of the incident solar radiation transmitted by the glass including both the solar direct transmittance and a portion of the absorbed radiation, which is re-radiated, expressed as a fraction.  See solar properties.

Total solar heat transmittance
The proportion of incident solar radiation transmitted by the glass, including both the solar direct transmittance and a portion of the absorbed radiation which is re-radiated, expressed as a fraction.  See solar properties.

Total transmittance
An alternative term for total solar heat transmittance.

Transluscent
Letting light through but obscuring clear vision.

Transmission
An alternative word for transmittance, expressed as a percentage.

Transmittance
The proportion of incident light or solar radiation transmitted by the glass, expressed as a fraction.  See optical properties and solar properties.

Transparent
Allowing through vision.

Ultraviolet transmittance
The proportion of incident UV radiation transmitted by the glass expressed as a fraction.

UV filter interlayer
An interlayer in a laminated glass that blocks the majority of the UV radiation.

UV filter layer
An alternative term for UV filter interlayer.

UV light
An alternative term for UV radiation

UV protection
An alternative term for UV reduction

UV radiation
The part of the electomagnetic spectrum with a slightly shorter wavelength than visible light, within the UV range, known as ultraviolet light or UV light.

UV range
The wavelengths of the electromagnetic spectrum usually described a being UV radiation.  There are two common descriptions, the ISO range and the Parry Moon range.

UV Reduction
The proportion of UV radiation that is blocked by the glass.

UV transmission
An alternative expression for UV transmittance, expressed as a percentage.

UV transmittance
The proportion of incident UV radiation transmitted by the glass expressed as fraction.

Visible spectrum
The part of the electromagnetic spectrum which is visible to the human eye, i.e. at wavelengths between 380nm and 780nm.

Wavelength
A character of electromagnetic radiation, by which it can be described.  Usually used to discriminate between different types of electromagnetic radiation, such as visible, UV and infrared (heat).