Electric light by the first practical electric arc light in 1806. By the 1870s, Davy's arc lamp had been successfully commercialized, and was used to light many public spaces. The development of a steadily glowing filament suitable for interior lighting took longer, but by the early twentieth century inventors had successfully developed options, replacing the arc light with incandescents. The energy efficiency of electric lighting has increased radically since the first demonstration of arc lamps and the incandescent light bulb of the 19th century. Modern electric light sources come in a profusion of types and sizes adapted to many applications. Most modern
Light crude oil less than 850 kg/m (API gravity greater than 35° API) The Mexican state oil company, Pemex, defines light crude oil as being between 27° API (893 kg/m) and 38° API (835 kg/m). This variation in definition occurred because countries such as Canada and Mexico tend to have heavier crude oils than are commonly found in the United States, whose large oil fields historically produced lighter oils than are found in many other countries. Canada also uses the SI of units to measure oil rather than American oil industry conventional units, and the base temperature for density calculations is different in