title: Add custom attribute to filter in product collection in magento
body: <p>I need to add custom attribute to filter for product collection</p>
  
  <p>I tried below code but filter is not working </p>
  
  <pre><code>$_productCollections=$this-&gt;getLoadedProductCollection();
  $_productCollection = $_productCollections-&gt;addAttributeToFilter('weight', array('lt' =&gt; 100));
  </code></pre>
  
  <p>below code is working </p>
  
  <pre><code>$collection = Mage::getModel('catalog/product')-&gt;getCollection();
  $_productCollection = $collection-&gt;addAttributeToFilter('weight', array('lt' =&gt; 100));
  </code></pre>
  
  <p>I need proper way to add filter range for weight attribute like</p>
  
  <pre><code>-&gt;addAttributeToFilter('weight', array('lt' =&gt; 100));
  </code></pre>
  
  <p>in default product collection(<code>$this-&gt;getLoadedProductCollection();</code>)</p>