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Glass Building

Reading glass specifications

The most important reason for choosing low iron glass is the increased colour rendering which results from the more natural colours of the glass and whatever material it is combined with. The parameter referred to as ‘Ra' in a glass specification sheet indicates the likely degree of correctness the colour will have while increasing the thickness of the glass panel. For clear white glass the Ra factor is very high and remains high while the thickness of the glass is increased. For the clear white glass the deviation Ra from a 4mm glass to 12mm glass is 0.6%, for normal glass the deviation Ra is 2.2%. This is taken from general specs of St Gobain glass Diamant (extra clear) vs. Planilux (normal float glass).

Another parameter is TL, light transmission properties, that varies with 1% for the Clear white glass from 4mm to 12mm, while for normal float glass it is decreasing rapidly with increasing thickness of the glass. For personal comfort in buildings it is highly desirable to have a high level or percentage of visible light transmission, in order to provide the inhabitant with a good visibility of his surroundings together with an increased feeling of spaciousness. That is why decorated glass used in buildings should always have a very high Ra factor.