MakeLongShadow

<Grid Background="DarkRed">
    <Rectangle x:Name="ShadowElement" />
    <TextBlock x:Name="TextBlockElement"
               FontSize="148"
               FontWeight="Bold"
               Foreground="Orange"
               Text="00:10:15" />
</Grid>

CompositionHelper.MakeLongShadow(188, 0.3f, TextBlockElement, ShadowElement, Color.FromArgb(255, 250, 110, 93));

Demo

you can run demo and see this feature.