掲示板 Forums - About adjectives and their past tense

I was playing around with building sentences with adjectives and for one sentence that I wrote in the past tense, I was wondering if I was supposed to add でした at the end of my sentence or use the past form of the adjective.

The sentence was : the red light was bright, warm and big.

I wrote : あかい　ひかり　は　かるくて　あたたかくて　おおきい　でした。

Feel free to correct and add insight please :)

Isn't 大きい an い-adjective? For past tense, you just simply conjugate the ~い with ~かった, and add です for 敬語.