Onclick open sub menu, Onclick close sub menu?

Onclick open sub menu, Onclick close sub menu?

On this page http://kimcolemanprojects.com/ I need to have a drop down menu that opens on click and closes again on click of same anchor. Like it works on this site http://angela-moore.co.uk/

this is my html for the menu so far:

<div class="left" id="nav"> <ul id="menu"> <li id="light"> <a href="lighting_video.html">Lighting + Video</a> <ul style="display: none;"> <li><a href="django_django.html">Django Django</a></li> <li><a href="suntrap.html">Suntrap</a></li> </ul> </li> <li id="photo"> <a href="photograms.html">Photograms</a> </li> <li id="about"> <a class="active" href="about.html">About</a> </li></ul> </div><!--end nav-->

As you can see I only need it to work within one list item. I need help writing the javascript for this.

Thanks for any help.