From this webpage:
In 1879, after testing more that 1600 materials for the right filament, including coconut fiber, fishing line, and even hairs from a friend's beard, Edison and his workers finally figured out what to use for the filament--carbonized bamboo.
I'm a little surprised it took Edison that many tries to get it right. 1600 different materials is quite a lot. Did Edison go through about 1600 tests? Are there any first-hand accounts that prove it?
(Note: the page does say that Edison took detailed notes (40,000 pages, apparently), so I would think he would have a detailed chronology and record of the tests there.)