yes, the title and discription are both in the lbcaption div.
you would need to edit the code that genrates the thumbnails on the page to add a <br /> tag, the font size for the description cant be changed though without effecting the title as well.
to add the <br> tag:
in the galleries/grid_lightbox/index.php file, change the following line:
echo '<a href="' . $fullsizeImgSrc . '" rel="lightbox-pg' . $random . '" name="<strong>' . str_replace('"', '\"', $row_images['title']) . (strlen($row_images['title']) > 0 ? ':' : '') . '</strong> ' . str_replace('"', '\"', $row_images['description']) . '"><img src="' . $imagePath . '" alt="" title="' . $i . '##' . str_replace('"', '\"', $row_images['title']) . '##' . str_replace('"', '\"', $row_images['description']) . '" alt="" width="' . $thumbnailInfo['width'] . '" height="' . $thumbnailInfo['height'] . '" /></a>'.PHP_EOL;
to:
echo '<a href="' . $fullsizeImgSrc . '" rel="lightbox-pg' . $random . '" name="<strong>' . str_replace('"', '\"', $row_images['title']) . (strlen($row_images['title']) > 0 ? ':' : '') . '</strong> <br>' . str_replace('"', '\"', $row_images['description']) . '"><img src="' . $imagePath . '" alt="" title="' . $i . '##' . str_replace('"', '\"', $row_images['title']) . '##' . str_replace('"', '\"', $row_images['description']) . '" alt="" width="' . $thumbnailInfo['width'] . '" height="' . $thumbnailInfo['height'] . '" /></a>'.PHP_EOL;