"Oh no, the lamp is broken!"
Translation:Voi ei, lamppu on rikki!
It's the subject of the sentence, and it's a countable noun.
Objects are very often partitive, as in 'Hän korjaa lamppua', "He's fixing the lamp". But most of the time, subjects are nominative like lamppu, not partitive like lamppua.
The only partitive subjects I can think of on Duolingo are in existential/possessive sentences, like 'Minulla on mehua', "I have juice".
And even there, the partitive subjects are always uncountable nouns, and they've all been following the possessor or location. If the word order is reversed, the noun tends to be nominative: 'Mehu on minulla', "I have the juice".