how to popup the lightbox to top window

I try to embed the dhtmlx gantt page in a iframe.the iframe will in a div.
how can i to popup the dhtmlx gantt lightbox to top window?
Pls help…

<div id="tabs-2"><iframe style="width:100%; height:500px" src="${BASE_PATH}/project/projectManage" scrolling="auto"></iframe>

${BASE_PATH}/project/projectManage will render a page of dhtmlx gantt.

If you have gantt in the iframe then lighbox can be snown only inside of frame area.
Why do you need to init gantt in the iframe in the first place ?