A local school board may pledge, as security for the payment of the principal and interest on any bonds or other special obligations issued pursuant to the School Revenue Bond Act, a part or the whole amount of income derived from an existing building, improvement or other facility subject to the control of the local school board. A local school board may pledge this income whether or not the existing building, improvement or facility is to be improved, repaired or furnished by the proceeds of the bonds or other special obligations.