Technical Barriers Sun-directing glass is commercially available. The only real barrier to its use is cost. Sun-directing glass also looks different from a normal window; it may appear to be somewhat “milky”, which may interrupt the design of the facade, especially if most of the facade is transparent glass.
4.9.2. Application The system is designed for use in direct sunlight. The best orientation on a facade is south in moderate climate zones (in the northern hemisphere). On west or east facades, it is only useful in the morning or afternoon. The system also deflects diffuse light, but the illuminance level achieved is much lower than with direct sunlight. Thus, for north facades, the elements have to be larger. The profile of the acrylic elements has been designed for specific latitudes. The optimum sun altitude for the sun-directing glass is between 10–65° (Figure 4-9.4). In tropical regions where sun altitudes are higher, the sun-directing glass should be installed at a tilted vertical angle so as to redirect more light. In this case, the geometry of the sun-directing elements will have to be changed to prevent glare. A light-directing rooflight should be installed with a slope of about 20° towards the sun.
4.9.3. Physical Principles and Characteristics Sun-directing glass deflects light in the horizontal plane as well as the vertical. Thus, light can reach the depth of a room for all solar positions without the need for movable parts in the building facade. Vertical deflection is achieved by the shape of the acrylic elements. Horizontal deflection is achieved either by holographic optical elements or by a sinusoidal glazing surface. Vertical Deflection Incoming light is focused by the first surface of the acrylic elements (Figure 4-9.4) and redirected by total reflection at the lower surface of the profile. It is spread slightly towards the ceiling when it leaves the elements.
Figure 4-9.4: Vertical section
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