Laravel:como adicionar cláusula where usando o construtor de consultas?

$query =  DB::table('elements');
$query->where('some_field', 'some_value');

// Conditionally add another where
if($type) $query->where('type', 1);

// Conditionally add another where
if($lang) $query->where('lang', 'EN');

$rows = $query->get();