Accurate　lightsource　location　or　direction　is　important　in　shape　from　shading　(SFS)　and　photometric　stereo　(PS).　Tracking　interested　object　by　the　lightsources　on　it　is　also　a　widely　used　positioning　scheme.　However,　existing　methods　for　lightsource　localization　are　primarily　designed　for　calibration.　They　are　usually　inferior　in　speed　and　accuracy,　because　of　the　intermedium　geometry　they　introduced.　Specifically,　they　must　recover　the　camera-intermedium　geometry　before　gaining　the　desired　intermedium-lightsource　or　camera-lightsource　geometries.　In　this　article,　we　propose　a　lightsource　localization　method　that　can　directly　recover　the　camera-lightsource　geometry.　A　sphere　and　its　shadow　are　used　as　the　intermediums,　but　their　roles　stay　in　the　images.　The　parallax　geometry　of　sphere　is　investigated　to　transfer　the　lightsource　localization　problem　into　solving　the　outer　bitangents＇　intersection　of　two　visible　conics.　The　solution　cases,　degenerated　cases,　error　distributions,　and　other　details　are　discussed　and　tested.　The　experiment　has　demonstrated　that　our　method　has　significantly　better　accuracy　and　robustness　than　the　state-of-the-art,　while　it　is　obviously　low-cost　and　lightweight.　　©　1963-2012　IEEE.