The right thing to do is to bentch licht in the Sukkah. It is wrong, however, to bentch licht in the Sukkah, and then to take the licht into the house. If absolutely necessary, at least stay in the Sukkah for a few minutes with the licht, then, if you must leave and the licht would then be left alone, and you are afraid to do so, take it into the house, and bring it back out for the seudah, when people go into the Sukkah.
On Yom Tov (NOT on Shabbos), you can bentch licht later (when people are in the Sukkah), so it may be less of an issue.
If you CANNOT have the licht in the Sukkah, or if it is not practical to do so, you must bentch licht where you will at some point in time benefit from its light.
I highly recommend, in the above case where you CANNOT have the licht in the Sukkah, to include the electric light in the Sukkah in your licht bentching as if it’s another candle. This is TRICKY now, because on Yom Tov, many women make the beracha first, and then light. You CANNOT do that if the electric light is one of your candles.
- Turn off the electric light in the Sukkah
- Light the candles (BEFORE the berachah, as if it were Shabbos)
- Turn on the Sukkah light, as your last candle (if you always light 2 candles, the electric light in the Sukkah is now your third, for example)
- THEN make the berachah.