To report a fault with a street light near you go to the Cambridgeshire County Council website and fill in the applicable form (see link below)
The submitted form will go directly to the local officer for the area and will also be logged onto the system for future reference and ensure your street light issue is recorded and dealt with according to their customer response standards.
Link to form: http://www.lightingcambridgeshire.com/contact-us/report-fault.htm