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;
	}
}