The correct answer here RE "an American thing" is "whatever is written into the contract as 'conveying' with the house." If you say "fixtures stay in the house

The correct answer here RE "an American thing" is "whatever is written into the contract as 'conveying' with the house." If you say "fixtures stay in the house" then they stay. If not, no obligation to leave them. Typically, however, these clauses deal primarily with appliances and other larger items (TVs, hot tubs, etc) In my experience people don't think to bring the bulbs with them, written or otherwise.