The amount of daylight transmitted through a window pane is reduced by the number of glass layers it has to penetrate.As a rule of thumb, double glazing(with no coating) lets in approx.80% of the light, while triple glazing(with no coating) lets in approx. 70%of the light (compared to an open window). Coloured or coated glass can reduce the visible transmittance of a window pane to values as low as 20% and significantly modify the spectral quality of the transmitted light, as well as the perception of surface colours in the interior.
» It is impossible to "optimise" buildings for good daylight performance with static glazing alone, since daylight intensity varies dramatically «
Shading and sun screening are just as important to good daylighting performance as the window itself. Pleated blinds and Venetian blinds can be used to adjust the amount of daylight entering spaces and to reduce window luminance to control glare. The Venetian blind can also be used to redirect the light into the room.
The most efficient shading solution to prevent direct solar radiation into the building is to use external shading. Examples of external shadings are roller shutters and awning blinds. A dark grey screen (VELUX awning blind 5060) will reduce the illuminance and luminance levels significantly to a level where the risk of glare is avoided.