Relation between var count, if and switch

1

this code from the flash AS3 documentation, i am trying to get familiar using filters, it really helped me a lot, there is one section i did not understand, please see the comments at the end of the code:


var distance:Number = 8;
var angleInDegrees:Number = 225;// opposite of 45 degrees
var colors:Array = [0xFFFFCC, 0xFEFE78, 0x8F8E01];
var alphas:Array = [1, 0, 1];
var ratios:Array = [0, 128, 255];
var blurX:Number = 8;
var blurY:Number = 8;
var strength:Number = 1;
var quality:Number = BitmapFilterQuality.HIGH;
var type:String = BitmapFilterType.INNER;
var knockout:Boolean = false;

var box:Shape = new Shape();
box.graphics.lineStyle();
box.graphics.beginFill(0xFEFE78);
box.graphics.drawRect(100, 50, 90, 200);
box.graphics.endFill();

var gradientBevel:GradientBevelFilter = new GradientBevelFilter(distance, angleInDegrees, colors, alphas,
ratios, blurX, blurY, strength, quality, type, knockout);
box.filters = [gradientBevel];

var stopLight:Shape = new Shape();
stopLight.graphics.lineStyle();
stopLight.graphics.beginFill(0xFF0000);
stopLight.graphics.drawCircle(145,90,25);
stopLight.graphics.endFill();

var cautionLight:Shape = new Shape();
cautionLight.graphics.lineStyle();
cautionLight.graphics.beginFill(0xFF9900);
cautionLight.graphics.drawCircle(145,150,25);
cautionLight.graphics.endFill();
var goLight:Shape = new Shape();

goLight.graphics.lineStyle();
goLight.graphics.beginFill(0x00CC00);
goLight.graphics.drawCircle(145,210,25);
goLight.graphics.endFill();

addChild(box);
addChild(stopLight);
addChild(cautionLight);
addChild(goLight);

var innerShadow:DropShadowFilter = new DropShadowFilter(5, 45, 0, 0.5, 3, 3, 1, 1, true, false);
var redGlow:GlowFilter = new GlowFilter(0xFF0000, 1, 30, 30, 1, 1, false, false);
var yellowGlow:GlowFilter = new GlowFilter(0xFF9900, 1, 30, 30, 1, 1, false, false);
var greenGlow:GlowFilter = new GlowFilter(0x00CC00, 1, 30, 30, 1, 1, false, false);

stopLight.filters = [innerShadow];
cautionLight.filters = [innerShadow];
goLight.filters = [greenGlow];

var timer:Timer = new Timer(3000, 9);
timer.addEventListener(TimerEvent.TIMER, trafficControl);
timer.start();

// i did not understand this section
// if you changed the value to 2, the order of light change too.
//please explain the relation between this var and the if and if with switch
var count:Number = 1;
function trafficControl(event:TimerEvent):void {
    // what is he comparing?
    if (count == 4) {
        count = 1;
    }
    // this is OK, i know that the switch swaps the lights between circles.
    // but this section still referring to the count var, why?  
    switch (count) {
        case 1 :
            stopLight.filters = [innerShadow];
            cautionLight.filters = [yellowGlow];
            goLight.filters = [innerShadow];
            break;
        case 2 :
            stopLight.filters = [redGlow];
            cautionLight.filters = [innerShadow];
            goLight.filters = [innerShadow];
            break;
        case 3 :
            stopLight.filters = [innerShadow];
            cautionLight.filters = [innerShadow];
            goLight.filters = [greenGlow];
            break;
    }
    count++;
}

Thanks for your help