What melacha is being violated by using a light dimmer on shabbos?
Answer:
The answer to this question is not clear.
There is no case here for boneh (as per the Chazon Ish). If there is a filament it can be hav’arah because you are “turning up the fire,” but for a LED or similar lamp there is no “fire” so this will not apply. According to some authorities the problem with electricity is Makeh BePatish (for instance Rav Asher Weiss), and perhaps this can even be applied to turning up the dimmer – but this is strained.
Thus, it is not clear which melachah is actually involved – yet of course the custom of all of Israel is not to permit doing this, at the very least as a “rabbinic” prohibition of refraining from using electricity on Shabbos.
Best wishes.
