if (document.images){
  but1e_0 = new Image();
  but2e_0 = new Image();
 

  but1e_1 = new Image();
  but2e_1 = new Image();
 

  but1e_0.src = "/images/specbutoff.jpg";
  but2e_0.src = "/images/optbutoff.jpg";
  

  but1e_1.src = "/images/specbuton.jpg";
  but2e_1.src = "/images/optbuton.jpg";
  
}

function light(button){
  if (document.images){
    document.images[button].src = eval(button + "_1.src");
  }
}

function dark(button){
  if (document.images){
    document.images[button].src = eval(button + "_0.src");
  }
}