Display Admin Form Field only Readonly in Magento

Add follwing code into _prepareForm() function.

$fieldset->addField('professor_firstname', 'text', array(
          'label'     => Mage::helper('deskcopy')->__('Professor First Name'),
          'readonly' => true,
          'name'      => 'professor_firstname',
      ));

OR
$fieldset->addField('professor_firstname', 'hidden', array(
            'label'     => Mage::helper('deskcopy')->__('Professor First Name'),
            'after_element_html' => '<tr><td><label for="title">Professor First Name</label></td>
                <td>' .$data['professor_firstname'] . '</td></tr>',
        ));