After lighting works have been purchased or constructed as aforesaid, in such city, the council may then raise and expend in making repairs or alterations, or in extending such works, such sum as it may deem advisable without submitting the question to the electors of the city; but the sum to be so raised in any 1 year shall be included in and shall not increase the total amount which by the provisions of section 5 of chapter 30 of this act the council is authorized to raise.