If any lights have been maintained by public subscription or by money supplied from the district road funds, within any territory which subsequently becomes a lighting district organized under this part, at the time of the establishment of such lighting district, or at the time of expiration of any then existing contract for the maintenance of such lights; such lights and the future cost of maintaining and operating them shall be included in the estimate of the governing body and shall thenceforth be maintained as a part of the lighting system of the district.