Optical Scaling is a design method which responds to optical influences of our vision. According to the pictured size a given proportion of black and white elements appears inconsistent: in small sizes thin black lines run the risk of disappearence and small white space seems even smaller—reverse large shown white space looks bigger than it actually is.
In the metal type era punchcutter reacted to those circumstances by a sensitive type design for each point size. By reducing all contrasts and details for small sizes and increasing selfsame for big sizes a typeface should appear consistent over the whole range of point sizes. This proceeding is still in use today as type designers create size specific variations of their fonts.
Legilux Serif comes with five optical sizes: Display (> 50 Pt), Headline (25–50 Pt), Subhead (13–24 Pt), Text (9–12 Pt) and Caption (< 9 Pt).