How many light bulbs are there in the world?

According to fastcompany.com: "Last year, U.S. consumers spent about $1 billion to buy about 2 billion lightbulbs--5.5 million every day."
According to wsj.com: "The U.S., which has four billion electric lights using [incandescent] bulbs, represents about a third of the world market."
So, about 12 billion bulbs, worldwide.