<script type="text/javascript" >
var value = 0;

      function setOpacity() {
         value += .7;
         var testObj = document.getElementById('test');
           
         testObj.style.width = "100%";
         testObj.style.height = "200%";
         testObj.style.display = "block";
         testObj.style.opacity = value/7;
         testObj.style.filter = 'alpha(opacity=' + value*7 + ')';
         myTimeout = setTimeout("setOpacity()", 1);
           
         if ((value/10) >= .5) {
            clearTimeout(myTimeout);
         }
        document.getElementById('warning').style.display = "block";
      }

      function removeOpacity() {
         value -= .3;
         var testObj = document.getElementById('test');
           
         myTimeout2 = setTimeout("removeOpacity()", 1);
         testObj.style.opacity = value/7;
         testObj.style.filter = 'alpha(opacity=' + value*7 + ')';
           
         if ((value/10) <= 0) {
            testObj.style.display = "none";
            clearTimeout(myTimeout2);
         }
        document.getElementById('warning').style.display = "none";
      }
</script>

<div id="test"></div>
<div id="warning">
<a href="javascript://" onclick="removeOpacity();">Включить свет</a>            
</div>
<div style="padding:10px 5 5px 5;position: absolute;">
<a href="javascript://" onclick="setOpacity();">Выключить свет</a>
</div>