radio.html

<!DOCTYPE html>
<html lang="en" dir="ltr">
  <head>
    <meta charset="utf-8">
    <title></title>
    <script>
      function check_value(onoff){
        switch(onoff){
           case "On":
             document.getElementById("myImage").src = "images/pic_bulbon.gif";
             break;
           case "Off":
              document.getElementById("myImage").src = "images/pic_bulboff.gif";
              break;
        }
      }
    </script>
  </head>
  <body>

<img id="myImage" src="images/pic_bulboff.gif" style="width:100px">
    <form method="post" action="">
      <input type="radio" name="switch" value="On" onchange="check_value('On')"> On<br>
      <input type="radio" name="switch" value="Off" onchange="check_value('Off')" checked="checked"> Off<br>
    </form>

  </body>
</html>