There is no standard height for a light switch. Home owners should install them at a height that is convenient to those using them. Generally, this is between 48 and 52 inches from the floor to the top of the electrical box.
In homes where an occupant uses a wheelchair, setting switches lower is more convenient. As of 2012, the Americans with Disabilities Act requires light switch installers to lower the switch to the 48-inch height to provide better accessibility in public facilities. While the ADA applies to new construction, existing public facilities are not required to meet the new standards.