How to autopostback radiobuttonlist without page refresh?

<ajaxToolkit:ToolkitScriptManager ID="ToolkitScriptManager" runat="Server" EnablePartialRendering="true" />
<asp:UpdatePanel ID="updatePanel1" runat="server">
    <ContentTemplate>
        Light Switch&nbsp;&nbsp;
        <asp:RadioButton ID="lightOn" AutoPostBack="true" runat="server"
            GroupName="switch" Text="Turn On" OnCheckedChanged="lightOn_CheckedChanged" />
        &nbsp;&nbsp;&nbsp;
        <asp:RadioButton ID="lightOff" AutoPostBack="true" runat="server"
            GroupName="switch" Text="Turn Off" OnCheckedChanged="lightOff_CheckedChanged" />
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
        <br />
        <asp:Label ID="Label1" runat="server"></asp:Label>
    </ContentTemplate>
</asp:UpdatePanel>

protected void lightOn_CheckedChanged(object sender, EventArgs e)
{
    Label1.Text = "Light has been turned on";
}
protected void lightOff_CheckedChanged(object sender, EventArgs e)
{
    Label1.Text = "Light has been turned off";
}

use update panel control and put the radio button list control inside the panel

and use a script manager and set the partialRendering property of script manager=true