How many light bulbs are used in a household in one year?

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.