Control Fields are specialized field spells typically cast over buildings and their surroundings. The purpose of a Control Field is to draw magical energy from a desired source and use it to power lighting and devices, repel intruders and slow degradation.
Like any other spell, a Control Field must be cast using natural magical energy, mana. However, what is exceptional about it is the fact that it can be maintained almost indefinitely using artificial magical energy. Huge power plants, that can convert the kinetic energy of a river or the thermal energy of a boiler into artificial magical energy, provide power for the Control Fields of common households and the industry.
A Control Field can be tailored to suit the needs of any household, facility or factory. It’s function may be something as minimal as energizing the lighting and heaters for a small house. On the other hand, a highly advanced Control Field can direct the energy flow inside a large semi-automated factory. Although most people lack the knowledge and spellcasting ability to create their own Control Fields, magic power companies are always eager to help them with the setup and maintenance. For a reasonable price, of course.