One trick is to use Fontographer -not FontLab- to generate an automatic weight shift and use that in the background as a guide.

And some rules of thumb: darker weights need more contrast, more width, tighter spacing, and a higher x-height.

More:
- Weights often get used in pairs, so plan them accordingly.
- Setting light-on-dark text makes a font look lighter; if you have a fine enough weight gradation you can build in an accommodation of this (meaning the color of weight_n will look equal to weight_n+1 reversed).
- You can make a -narrow- range of weights uniwidth (meaning changing the weight doesn't affect linebreaks). Beyond this range you can still use a favorite trick of mine: make them "fixed offset", which means applying let's say +5 tracking to the Light makes it uniwidth with the Regular.

See also De Groot's non-linear scaling method (which some people don't believe in however).

hhp

Something else:
Although I'm still not buying this new trend (championed by Yanone and Hasebe) of making each weight/style its own animal (it seems too self-indulgent, and really, that's what different fonts are for) I do think there's a threshold beyond which a weight is too light/dark to be used as a text face and that means it can -and probably should- have a different nature.

hhp

Thanks for your insight hrant.

One thing I am certainly not doing is making the lighter weight its own animal. To me, the whole point of different weights is to keep a continuity throughout the face. I do tend to agree that if one decides to make them too different it should be a different font.

You have given me some avenues to pursue.