Sunglasses allow better vision in bright daylight, and may protect one's eyes against damage from high levels of ultraviolet light. Typical sunglasses are darkened for protection against bright light or glare; some specialized glasses are clear in dark or indoor conditions, but turn into sunglasses when in bright light. Most sunglasses do not have corrective power in the lenses; however, special prescription sunglasses can be ordered. Specialized glasses may be used for viewing specific visual information (such as stereoscopy) or 3D glasses for viewing three-dimensional movies. Sometimes glasses with no corrective power in the lenses are worn simply for aesthetic or fashion purposes. Even with glasses used for vision correction, a wide range of designs are available for fashion purposes, using plastic, wire, and other materials. According to the carrying capacity, there are minivans (under 1.8 tons), light trucks (1.8-6 tons), medium goods vehicles (6-14 tons) and heavy trucks (over 14 tons). The UK glass industry is pursuing an active programme on energy efficiency and decarbonisation. But building the business case to secure funds remains a barrier. Capital costs can be very high and paybacks periods are often in excess of two years; traditional loans are usually unattractive for this work. In the early 20th century, famous American economist elvin fisher developed the theory of economic gain. In its book "the nature of capital and yield", first, the concept of yield is analyzed in terms of the performance of earnings, and three different types of benefits are proposed: