public function csvUnique($id){

          $date1= ''.$id.' 00:00:00';
          $date2= ''.$id.' 23:59:59';

        Excel::create('Customer list', function ($excel) {

         $excel->sheet('Sheetname', function ($sheet) {

             echo  $date1;
             echo  $date1;

             });

            })->export('csv');

} //end csv

**Undefined variable: date1**

function ($sheet, $date1, $date2)

global $date1;
global $date2;

Excel::create('Customer list', function ($excel) use ($date1, $date2) {

     $excel->sheet('Sheetname', function ($sheet) use ($date1, $date2) {
         echo  $date1;
         echo  $date1;
     });

})->export('csv');