function lightup(imgName) {
   	if (document.images) {
      imgOn=eval(imgName + "_on.src");
      document[imgName].src= imgOn;
	}
}
function turnoff(imgName) {
   	if (document.images) {
      imgOff=eval(imgName + "_off.src");
      document[imgName].src= imgOff;
   	}
}