5.1.8.1 General
Glare results from excessive contrast of illumination, or from an excess of illumination in the field of view. Reaction to it is subjective. When correctly designed, natural lighting should not be a glare problem.
NOTE — Contrasts in excess of 10 : 1 in illumination in different parts of the field of view might give rise to glare in some form.
5.1.8.2 Disability glare
Reducing the light transmission of glazing from 87 percent to 60 percent produces a just perceptible reduction in disability glare caused by direct sunlight. Even when the light transmission of the glazing is as low as 10 percent some 10 000 lux can still be experienced and glare shall almost certainly occur.
Glare can be reduced by some form of mechanical shading, for example a canopy, an overhanging floor, a balcony or a louvre system. Alternatively, internal screening can be provided by louvres or blinds.
NOTE — Any fixed shading system reduces the amount of natural light entering the building throughout the year, irrespective of whether there is a glare problem at any particular time.
It may also be possible to re-orientate the glazing to avoid entry of direct solar radiation. Alternatively, the interior layout can be suitably designed to eliminate glare.
5.1.8.3 Discomfort glare
Glazing products with light transmission lower than 50 percent can ameliorate discomfort glare. These products decrease the sky luminance components but permanently reduce the admission of daylight. Alternatively, shading devices, internal or external, movable or fixed, may be used.
PART 6 STRUCTURAL DESIGN — SECTION 8 GLASS AND GLAZING
Other methods of reducing the problems of glare should be considered, including,
a) installation of windows in more than one wall to raise the general background illumination and, in so doing, to reduce the contrast between a window and its surrounding surfaces;
b) use of light coloured matt finishes for the window frames and the surrounding surfaces;
c) splayed reveals, to assist in reducing the contrast between the window and its surroundings;
d) use of slender glazing bars and transoms of high reflectance; and
e) lowering window sills to allow increased illumination to enter, which increases the adaptation level and reduces the likelihood of discomfort glare.
5.1.9 Diffusion and Obscuration
The nature of some glazing products (for example, patterned or acid etched glass) can cause the direct incident solar beam to be scattered diffusely. Hence the window might assume an uncomfortable high brightness and become a discomfort glare source in its own right. Diffusing glazing used within the normal field of view should be used with caution.