Low-E coatings, as they are referred to, is the shorthand for Low Emissivity coatings that are applied to most insulated glazed units in modern architecture and construction.
Emissivity is the amount of radiant energy a material absorbs. When it comes to thermal insulation in buildings and projects you do not want the external elements of the construction to absorb the heat from the internal space, you want this radiant heat energy to remain within the internal spaces in order to maintain a constant heat level internally and reduce heat loss to the external environment.
Levels of emissivity are measured on a scale of 0 to 1; a level of 1 would signify full radiant energy absorption and a level of 0 would signify a material that reflected 100% of energy directed at it.
Glass naturally has quite a high emissivity value, at around 0.89 for standard, uncoated float glass. Low Emissivity coatings are applied to glazing units in order to reduce the amount of heat that glazing units absorb and, therefore, emit to the external of a space. These Low-E coatings reflect radiant heat back into the internal spaces, improving the thermal performance of the glass unit.
There are criticisms of Low-E coated glass amongst them designing circles as reflection is inversely proportional to emissivity, so the lower the emissivity, the higher the reflectivity of the material. This makes glass units less transparent and more visible in architectural design when a low-e coating is used. Unfortunately little can be done about this in a time where thermal performance criteria are needed in order to maintain the energy efficiency standards across all building sectors.
The use of low iron and anti-reflective glass will reduce the visibility of glass units used in architectural design.
Low-E coatings are a must for all insulated glass units in order to achieve the thermal performance criteria demanded by Building Regulations Part L.