This difference in reflectivity decreases as the season progresses toward the winter solstice, and in winter the tilted and vertical windows transmit essentially the same amount of solar energy. Schematic arrangement of a tilted window in a south facade. Reflectivity of glass can be increased by coating the surface with either a very thin metallic film or a film of dielectric material that has a high index of refraction. Sealed double glazing units are now available with a reflective coating on the inside surface of the outer pane. Their reflectivity depends on the angle of incidence just as for uncoated glass, but the value at all angles of incidence is higher than for ordinary glass.
Blinds provide another method of solar control.
A light coloured blind reflects some of the solar radiation and absorbs the rest. This causes the blind to heat until it is losing heat at the same rate as it receives it from the sun. If the blind is in the room, most of the energy it absorbs is added to the room's cooling load. If it is between the panes of a double window, however, some of the absorbed energy is transferred to the outside air and the room's cooling load is reduced accordingly. It is desirable therefore, to use light coloured blinds and, if possible, to place them between the panes, of a double window.