var lightNum = 0;
var iterations = 0;

function switchLights()
{
	var oldDiv = "divLights0" + lightNum;
	lightNum = lightNum + 1;
	lightNum = lightNum % 10;
	var newDiv = "divLights0" + lightNum;
	document.getElementById(oldDiv).style.visibility = "hidden";
	document.getElementById(newDiv).style.visibility = "visible";
	iterations++;
	if (iterations < 20)
	{
		setTimeout('switchLights()',500);
	}
}