Thanks, after an hour i finally found the command to turn the light from 0 (off) - 100 (max brightness)
curl -i --digest -u admin:password -X PUT -d '<SupplementLight><whiteLightBrightness>10</whiteLightBrightness></SupplementLight>' http://192.168.x.x/ISAPI/Image/Channels/1/SupplementLight