The LineHeightInPixels represents the height of a line of text in pixels. A line of text includes the tallest letters (such as capital letters) as well as letters which have pixels that fall below the base of the line (such as the lower-case letters 'p', 'q', and 'y').
The LineHeightInPixels is the value used by FlatRedBall when determining the size of text in the SetPixelPerfectScale. A Text object which is drawn in 2D mode (where one unit equals one pixel) will have the following relationship to the LineHeightInPixels property of its BitmapFont: