Display Progress Bar while Exporting DataTable to Excel in ASp.Net

well i figured it out. I placed a timer in my HTML code and the progress bar hides after the download is completed

<asp:UpdatePanel ID="UpdatePanel2" runat="server">
        <ContentTemplate>
            <asp:Timer ID="Timer1" runat="server" Interval="2000" />
        </ContentTemplate>
    </asp:UpdatePanel>

Honestly I dont know why its working. Maybe someone can explain why.