All font weights other than FontWeight.BOLD are ignored. To get the light font you want to do something like this:

    private static final Font UNIT_FONT = Font.font("Segoe UI", FontWeight.LIGHT, 24);

We have the API but it is ignored and not implemented at the moment. The only way to get a light font is via its name not family name. Like:

    private static final Font UNIT_FONT = new Font("Segoe UI Light",24);

You can see where it is ignored in:
com.sun.javafx.font.PrismFontLoader#font(String family, FontWeight weight, FontPosture posture, float size)

It even has a comment that we should come back and fix it :-)


        // REMIND. Some day need to have better granularity.

        boolean bold = weight != null &&
                       weight.ordinal() >= FontWeight.BOLD.ordinal();
        boolean italic = posture == FontPosture.ITALIC;
        PGFont prismFont = fontFactory.createFont(family, bold, italic, size);

So at the moment its just treated as 2 booleans not a enum from Prism down.