Something that will fill the room

On his deathbed an old man calls his 3 sons and tells them that all he has is a sack of gold, which will go to the smartest son. He then gives them 1 dollar each and tells them to return at 9pm with something that will fill the room.
The first brings a bag filled with fine cotton.
The second brings a balloon filled with air.
But he gives the bag of gold to his third son.
What did he bring ?

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The third son brought a Candle and match and filled the room with light.