Close LightBox

does anyone know how to close a lightbox after you click on a submit button. I am using an HTML code on a page and I call that page from a button. That part works great. But after I click on the submit button, using a PHP file. The file that it calls opens up in the lightbox. So I think I need to close it first before it opens open the window.

Below is what I am doing in the PHP file
mail($to,$subj,$message);

header("Location: requestthankyou.html");


I need to close the light box before it brings up new page.

Thanks for any help