In the United States, the CD-Rom will tell you that the answer is Thomas Alva Edison, the man who coined the phrase that genius is "1 per cent inspiration and 99 per cent perspiration".
But in Britain, the computer will tell you that Joseph Swan demonstrated an electric filament light bulb in Newcastle-upon-Tyne on 3 February 1879 - just over eight months before Edison's team at Menlo Park, Virginia, produced an electric-powered bulb.
Similarly, when it comes to the telephone, who was the bright spark? In the US and British versions, you will learn that it was Alexander Graham Bell. In the Italian version the kudos goes to Antonio Meucci, a candlemaker who it says called the phone into being five years before Bell did. Similar differences exist over the discovery of HIV, the virus that causes AIDS.
Microsoft yesterday admitted the difference exists, but said that with such issues "the answers are rarely black and white". Even if you think you know what a light bulb is, defining who produced the first electric light bulb is a different matter: is it the first to demonstrate it in public, to patent it, or to put it into commercial production?
Richard Teversham, Microsoft UK's consumer product manager, suggested yesterday that the discrepancies actually indicate the product's rigour: "The British version is put together by a team of 65 people sitting in London, who put the information together from a British perspective."
Other local teams will put their local perspective on the definitive version of history. "The French version probably has an entry on Agincourt which isn't quite the same as the British one," he said.
Microsoft first released Encarta, an interactive encyclopaedia based on the 29-volume Funk & Wagnall New Encyclopaedia, in 1993. Producing that original took more than two years with a team of 130 people; now there are nationalised versions for the US, UK, France, Germany, Italy, Spain, Holland, Japan, Brazil and Sweden.
The US version contains more than 40,000 words and 45,000 articles - which points up another cultural difference, according to Mr Teversham: "The British version contains different articles. We have also noticed that, in Britain, people also require more in-depth articles than in the US."
Some British PC owners may not be getting the advantage of those changes, though. Many American computer brands sold in the UK include versions of Encarta bought in the US, not the UK. Only versions of Encarta bought off the shelf in the UK are certain to be the localised version.
However, the differences over who invented the light bulb are minor compared to the far more subtle - but inflammatory - ones of border disputes. The names and boundaries of islands and countries is so delicate a matter that Microsoft's US headquarters in Redmond, in Washington state, employs one person whose job is to investigate disputes and talk to governments about their borders - so that the Microsoft Atlas will be as accurate, and uncontroversial, as possible.
Two Men, One Bright Idea
Born on 11 February, 1847 in Milan, Ohio. His first invention at the age of 16 was an automatic telegraph signaller. In March 1876 he moved into Menlo Park, his "invention factory" in New Jersey, built with the help of his father. The first project was a phone that people could use without shouting. Edison put his name to up to 400 patents a year. The light bulb finally worked on 21 October 1879. A public demonstration took place on New Year's Eve.
Born in Sunderland on 31 October 1828. He began his career as an apprentice to a local chemist. Some of his earliest work was in photographic printing: he also patented the first bromide paper in 1879. He demonstrated the first useable electric light bulb in Newcastle upon Tyne on 3 February 1879 - Mosley Street in the city centre was the first street ever to be lit by electric light. In 1881 the same system, using 1,200 bulbs, was used to light the Savoy Theatre in London.Reuse content