Incandescent lights work by turning heat into light. You run an electric current through a filament, the filament heats up, and as it does, it starts to glow. The basic element has been around since 1809. The trick is finding material for a filament that will get hot enough to glow, but won't destroy itself too quickly. In fact, that's really the breakthrough Thomas Edison brought to the table in 1879. His carbonized bamboo filament lasted for 1200 hours—long enough to make the investment in a light bulb worth it. According to sources I found in the Wisconsin Historical Archives while researching my upcoming book on the past, present, and future of electricity, one of Edison's bulbs cost the equivalent of $36 in 1882.
This is not one of the earliest Edison bulbs. It's a later model, with a tungsten filament, dating to 1912. It was found in a time capsule at NELA Park, the General Electric headquarters and research laboratory that was opened that year. There were five light bulbs in the time capsule. This is the only one that GE engineers were able to get to light up. In the video, you can see it faintly glowing, 100 years after it was squirreled away.