window.onload = function() {
	if ( document.getElementById ) {
	   var cell = document.getElementById('cells');
	   var divs = cell.getElementsByTagName('div');
	   for ( var i in divs ) {
	     divs[i].onmouseover = function() { this.className = this.className +  ' light'; }
	     divs[i].onmouseout = function() { this.className = this.className.replace(/ light/g, ""); }
           }
 	}
}