<fx:Declarations>

<mx:Glow id="glowOver"
                 duration="1000"
                 alphaFrom="1.0" alphaTo="0.3"
                 blurXFrom="0" blurXTo="15"
                 blurYFrom="0" blurYTo="15"
                 color="0x333333"
                 />
        <mx:Glow id="glowOut"
                 duration="1000"
                 alphaFrom="0.3" alphaTo="1.0"
                 blurXFrom="15" blurXTo="0"
                 blurYFrom="15" blurYTo="0"
                 color="0x333333"/>
    </fx:Declarations>

flex4mxml里设置方法：  

<s:Label  rollOverEffect="{glowOver}" rollOutEffect="{glowOut}"/>

flex4script里设置方法： 

<fx:Script>
    <![CDATA[

            var labelNum:Label = new Label();

           labelNum.setStyle('rollOverEffect', glowOver);

          labelNum.setStyle('rollOutEffect', glowOut);
   ]]>
</fx:Script>