The electric light bulb was invented much earlier than most people realize. That is, if you don't mind a light bulb that burns out in two or three hours. There's a reason most sources qualify Thomas Edison's achievement as the man who invented the first practical, long-lasting light bulb. The idea was more than a half-century old by the time Edison and Joseph Swan (the Briton who invented the carbon filament bulb nearly simultaneously to Edison) made commercially viable designs. As is often the case, the invention everyone remembers only made the leap from theoretical possibility to practical reality because of a much less glamorous invention (and inventor) nobody remembers. You can stop reading at this point if you've heard of Hermann Sprengel.
As early as 1800 scientists working with electricity demonstrated all of the principles necessary to create electric light. Humphry Davy used a platinum filament and a huge amount of current in 1802 to generate a feeble light – not much, but considering Edison and Swan didn't patent their bulbs until 1879 it demonstrates just how old the idea was. In fact, by the 1840s there were any number of patents for incandescent bulbs of varying designs and materials. Of particular interest is the mysterious American John Starr, who patented a bulb in 1845, died immediately of cholera, and disappeared from the historical record. Nothing is known about him and only the diligent archiving of the US Patent Office allows us any evidence that he existed. His design was never exploited commercially.
Part of the problem in developing electric light was obvious – the "electric" part was lacking. Any home that wished to make use of electric appliances prior to 1880 had to build its own electric generator on-site. This is where Edison succeeded, and really truly succeeded, in a way neither Swan nor anyone else did. He didn't just invent a bulb; he convinced Gilded Age New York industrialists to build a power grid across the city. Many people had designs for bulbs but only Edison had a design for how to get light bulbs from patent drawings and laboratories into houses and places of business.
The two major obstacles to the design of the bulb itself, independent of electricity, were the material of the filament and the ability to remove air from the bulb (to extend the life of said filament). Every manner of material on Earth was tried and rejected as a suitable filament once the basic principles and components of incandescent light were understood. Eventually a thin piece of carbon – charred wood shavings, bamboo, or even paper – through which current could flow in a vacuum was identified as the answer (metal filaments of tungsten and tantalum were invented just after 1900 and put the German giant Siemens on the industrial map). But that was all well and good except that nobody could achieve a suitable vacuum during bulb manufacture. Enter Hermann Sprengel.
The German engineer developed a device, universally called the Sprengel Pump, that enabled air pressure to be reduced to less than one-millionth of its atmospheric level. While not a perfect vacuum it was more than close enough to enable the light bulb to make the leap from idea to mass produced reality. Incidentally, the Sprengel Pump relied upon a process involving considerable amounts of mercury, so many early Edison researchers and workers lost teeth, sanity, or central nervous system functioning in service of achieving that elusive vacuum. It is not unfounded to wonder if Edison himself had a touch of the Mad Hatter syndrome, as he worked with the device intimately and was known to be, you know, a dick. But that is merely speculation.
So without Hermann Sprengel there is no light bulb, and without the light bulb there is no Thomas Edison as he is known and revered today. And don't mention Edison around the British. They're still a bit sensitive about Joseph Swan getting the historical shaft.