Accessing js frameset function from child frame

I've got a javascript include that's declared in the head of the frameset of a site, this js file has a number of methods in it. I need to call the method from one of the framesets child frames but can't quite figure it out, could someone help me out? Here's my call that's not working:

<a href="javascript:window.parent.launchLightbox('start');">launch lightbox</a>

Unfortun开发者_运维知识库ately the js needs to be added to the frameset as the lightbox needs to fill the whole screen and not just in the dimensions of the child frame where the above code sits.

Thanks, Colin.

I think you can access it with window.top (coming from my memory though)