scratch_16.php

<?php

$xml = simplexml_load_file('arxeio1.xml');
$filters = $xml->xpath('products/product/filter');
foreach($filters as $filter) {
    $feature_name = trim($filter->filter_name);
    if ($feature_name == "ΙΣΧΥΣ/WATT") {
        // Do something
        echo "1<br />";
    } elseif ($feature_name == "LUMEN") {
        // Do something else
        echo "2<br />";
    }
}

$xml = simplexml_load_file('arxeio2.xml');
$filters = $xml->xpath('products/product/attributes/attr');
foreach($filters as $filter) {
    $feature_name = trim($filter->name);
    if ($feature_name == "Dimmable") {
        // Do something
        echo "3<br />";
    } elseif ($feature_name == "Αριθμός Λαμπτήρων") {
        // Do something else
        echo "4<br />";
    }
}