Can I still produce a product and attempt to sell it if it has already been made?

Ok, for example whoever invented a wooden pencil...they had the patent to make a wooden pencil....but when a led pencil came out...was it a whole new patent? so what im asking is...if i see a product that is already invented...actually is a concept. Can i still improve there concept and make it into my own product... show more Ok, for example whoever invented a wooden pencil...they had the patent to make a wooden pencil....but when a led pencil came out...was it a whole new patent? so what im asking is...if i see a product that is already invented...actually is a concept. Can i still improve there concept and make it into my own product even though its a product already? Can i apply for a whole new patent since in reality it would be a completely different product although it has the same base as the concept. would i interfere with there patent? hopefully everyone understands what im asking.
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