This does not work. Why? Because, depending upon the font family, there are basically only two font weights: normal and bold: 100 to 600 generally equate to normal, and 700 to 900 equate to bold. This is because "normal" is generally drawn with a line thickness one pixel wide, and "bold" is 2 pixels wide. You cannot get lighter than one pixel wide, and more than two pixels wide would look gross, as is the case with the font-family "Impact". Try:
and you should see what I mean...