Paste the following before </style>

.flContainer {
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    overflow: hidden;
    z-index: 998;
    position: fixed;
    top: expression(
        document.getElementsByTagName( 'body' )[0].scrollTop + "px"
    );
    pointer-events: none;
}
.fl {   
    width: 5000px;
    height: 5000px;
    position: absolute;
    overflow: hidden;
    z-index: 999;
    visibility = "visible";
}
.flspot {
    background-image: -webkit-gradient(radial, 50% 50%, 0, 50% 50%, 350, color-stop(25%, rgba(0, 0, 0, 0)), color-stop(100%, #000000)); 
    background-image: -webkit-radial-gradient(center center, closest-side circle, rgba(0, 0, 0, 0) 25%, #000000 100%);
    background: radial-gradient(closest-side circle at center center, rgba(0,0,0,0) 0%,rgba(0,0,0,0.01) 25%,rgba(0,0,0,1) 100%);
    background-image: -moz-radial-gradient(center center, closest-side circle, rgba(0, 0, 0, 0) 25%, #000000 100%);
    background-image: -ms-radial-gradient(center center, closest-side circle, rgba(0, 0, 0, 0) 25%, #000000 100%);
    background-image: -o-radial-gradient(center center, closest-side circle, rgba(0, 0, 0, 0) 25%, #000000 100%);
    width: 900px;
    height: 900px;
    position: absolute;
    overflow: hidden;
    z-index: 999;
    visibility = "visible";    
}
#lightswitch {
    z-index:1001;
    position:fixed;
    top:15px; left:15px;
    padding:5px 5px 2px;
    background: black;
    }
#lightswitch a:link {
    color: yellow;
}

Paste the following before </head>

<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>
<script type='text/javascript'>
    $(document).ready(function() {
        $(".flContainer").css({
            display: 'block'
        });
        $("#fl").css({
            top: ($(window).height()/2 - 2500) + "px",
            left: ($(window).width()/2 - 2500) + "px"
        });
        $(document).mousemove(function(e){
            $("#fl").css({
                top: (e.pageY - $(window).scrollTop() - 2500) + "px",
                left: (e.pageX - 2500) + "px"
            });
        });

        // fallback for IE
        $("#fl").click(function (event) {
            $(this).toggle();
            var link = document.elementFromPoint(event.clientX, event.clientY);	// IE & FF
            $(this).toggle();
            if (link.tagName.toLowerCase() == 'a') {
                window.location.href = link.href;
            }
            $(link).trigger('click');
        });
        if ( getCookie("flashlight") != "on" ) ToggleLights();
    });

    function getCookie(name) {
      var parts = document.cookie.split(name + "=");
      if (parts.length == 2) return parts.pop().split(";").shift();
    }
    
    function ToggleLights() {
        var fldiv = document.getElementById('fl');
        if (fldiv.style.display !== 'none') {
            //Turn flashlight off
            document.cookie = 'flashlight=off; path=/'
            fldiv.style.display = 'none';
        }
        else {
            //Turn flashlight on
            document.cookie = 'flashlight=on; path=/'
            fldiv.style.display = 'block';
        }
    }
</script>

Paste the following before </body>

<div class="flContainer">
    <div class="fl" id="fl">
        <div style="position:absolute; background: black; top:0px; left:0px; width:5000px; height:2050px; overflow:hidden;"></div>
        <div style="position:absolute; background: black; top:2050px; left:0px; width:2050px; height:900px; overflow:hidden;"></div>
        <div class="flspot" style="position:absolute; top:2050px; left:2050px; width:900px; height:900px; overflow:hidden;"></div>
        <div style="position:absolute; background: black; top:2050px; left:2950px; width:2050px; height:900px; overflow:hidden;"></div>
        <div style="position:absolute; background: black; top:2950px; left:0px; width:5000px; height:2050px; overflow:hidden;"></div>
    </div>
</div>

<div id="lightswitch">
    <a href="javascript:void(0);" onclick="ToggleLights();" target="_self" >LIGHTS</a>
</div>

More advanced stuff you can do:

• • Elements with a z-index over 1000 will show up even when the lights are off.
• • Cool effects with transparent PNGs and z-index. See: The skulls on my blog
• • Set the background-color and other elements' colors in the ToggleLights code.