<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>