Hi,
it should work when you specify the complete name of the font in the attribute FontName. For example, to get the 'light' version of the font Roboto, specify Roboto Light in the attribute as shown in the screenshot below:
Please note, sometimes the font variant names are localized. The bold version of Arial, for example, is named in German Arial Fett. In such case, using Arial Fett as name results in the same as enabling the attribute Bold for the font Aria.
Best regards
Paul Banach