Whats the most +light -light resist on a char?

[Louros]

like if i wanna socket light facets into all my items. what the max i can put that it wont do any more?

[stephan]

+%lightning damage is not capped, but gets added to your mastery so not very effective. A player's/monster's resistance cannot be lower than -100.

[ProfessionalBerg]

Theoretically, a monster might have 99% lightning resist after breaking its immunity with Conviction/Lower Resist. That means that you have 199% to go before reaching -100% resist. But that'd be a waste of time, IMHO, since all non-LI monsters have less than that.

As to how much -lres you can have on gear, let's count:

Crescent Moon runeword: -35%
4xFacets in shield: -20%
4xFacets in armor: -20%
Perfect Griffon's Eye with a Facet: -25%

All in all, -100% lres. Plus Infinity, plus Lower Resist, but those work only at 1/5th if breaking an immunity. So, the most you can bring down an initially LI monster to is around -10%~0% lres. Sacrificing lots of gear for it, which I do not recommend.

[EDIT]: Instead of Crescent Moon and the shield, you could use a -55% lres infinity, but that'd still leave you pretty fragile as a Sorceress (no shield for resists/block), and there are no +skills on it either.