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;
    }
}