The incandescent light bulb was perhaps Thomas Edison's most significant invention, and the one that brought him the most fame. This long-burning new invention made it far more practical and inexpensive to use in city street lights, and it also found commercial application, allowing mills, factories, and other institutions, like hospitals, to run throughout the night. The incandescent bulb (or using many of them at the same time) also required tremendous amounts of energy, creating a demand for safe methods of generating energy for large areas. Edison wrongly thought direct current the best method for doing this. His invention, however, ushered in what might be called the Age of Energy, where new forms of energy made increased production possible even as they created their own demand.