The trustees may purchase street lighting service and facilities and may levy an annual tax not to exceed fifty-four cents per thousand dollars of assessed value for the purpose of exercising the powers granted in this chapter. This levy shall be optional with the trustees, but no levy shall be made unless first approved by the voters as provided herein. The trustees may purchase material, employ labor, and may perform all other acts necessary to properly maintain and operate the benefited street lighting district. The trustees shall be allowed necessary expenses in the discharge of the duties, but shall not receive any salary.