I have found most dictionary definitions of joy to be sadly lacking:
The passion or emotion excited by the acquisition or expectation of good; pleasurable feelings or emotions caused by success, good fortune, and the like, or by a rational prospect of possessing what we love or desire; gladness; exhilaration of spirits; delight. http://www.brainyquote.com/words/jo/joy181774.html
My conception of joy is of something more profound.
Joy is to be found in a place of inner quiet, the point of light within – the divine spark? It is more the manifestation of a quality of spirit than an emotion, existing only in the ‘now’.