Perhaps the greatest improvements in building construction have been in heating, cooling, ventilation, lighting, and sound control. In most large buildings complete, year-round air conditioning is now standard. Some areas in a building may need to be cooled even in winter, depending on the distance from exterior walls and the heat generated by lighting, electrical equipment, or human occupancy. The level and quality of lighting have improved greatly. Largely as a consequence of these changes, the cost of the mechanical and electrical systems in buildings has increased at a greater rate than other individual building costs; such costs currently account for a quarter to a third of total construction expenditure. Increasingly since the late 1970s all these systems are automatically operated and controlled by computers that are programmed to maximize efficiency and minimize waste and energy consumption.