Yii Is Not Logging

application.log is empty,yii not writing to log

have
defined('YII_DEBUG') or define('YII_DEBUG',true);
// specify how many levels of call stack should be shown in each log message
defined('YII_TRACE_LEVEL') or define('YII_TRACE_LEVEL',2);


main.php
'class' => 'CLogRouter',
'routes' => array(
array(
'class' => 'CFileLogRoute',
'levels' => 'error, warning',
),

but not writing to application.log