Die Lampe ist klasse, sie ist nicht langweilig.
Why is there sie after the comma, is that sie for lampe (die Lampe).
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Sign up to join this communityThe word »sie« is not an article! It is a personal pronoun. It refers to a noun or a nominal group that has feminine gender. A personal pronoun always can be replaced by the noun or a nominal group to which it refers (you just need to correct the grammatical case if it is different).
Here »sie« refers to a nominal group, and this group consists of two words:
Since sie also is in nominative case, you don't need to change case when you replace the personal pronoun by the nominal group:
Die Lampe ist klasse, die Lampe ist nicht langweilig.
We have two full sentences here, which are joined together by a coma. You could separate them with a full stop too:
Die Lampe ist klasse. Sie ist nicht langweilig.
Die Lampe ist klasse. Die Lampe ist nicht langweilig.
An example where you need to change the case when you replace:
Der Berg ist hoch. Ich werde ihn morgen besteigen.
»Berg« is a masculine noun. Here der Berg is in nominative case, but the personal pronoun »ihn« which refers to the nominal group »der Berg« is in accusative case. So, the replacement must be in accusative case too:
Der Berg ist hoch. Ich werde den Berg morgen besteigen.