An HBO documentary about the relationship between actress and writer Carrie Fisher and her Hollywood legend mother, Debbie Reynolds, will air Jan. 7. “Bright Lights: Starring Carrie Fisher and Debbie Reynolds,” was expected to premiere on the cable network this spring but HBO moved it up after the pairs’ deaths. Although it hasn’t been on television, “Bright Lights” was shown earlier this year at film festivals in New York and at Cannes.