 The switching is done by applying a voltage to the material, or by performing some simple mechanical operation.Windows, skylights, etc., that are made of smart glass can be used to adjust indoor lighting, compensating for changes of the brightness of the light outdoors and of the required brightness indoors.The use of heliostats, mirrors which are moved automatically to reflect sunlight in a constant direction as the sun moves across the sky, is gaining popularity as an energy-efficient method of lighting.