125-Year-Old Lightbulb Still Glows With 'NO' Filament

More info from GROK:

The exact chemical composition of the filament is not fully known today because the manufacturing process was proprietary and largely lost when Shelby Electric was acquired (the patents describe the lamp design and shape but not the filament chemistry in detail).

**What is confirmed by direct testing:** - It is **pure carbon** (confirmed via X-ray spectroscopy and Auger spectroscopy at Sandia National Laboratories on a similar Shelby bulb). Surface analysis showed only carbon, with minor white silica flecks likely from the glass envelope—no metal plating. - It behaves as a **semiconductor** (negative temperature coefficient of resistance: hotter filament = lower resistance / more current flow, opposite of tungsten). - Likely produced from sheets of material via Chaillet’s “secret chemical process,” then automatically square-cut into filaments (similar to early carbonized organic fibers like cotton/linen/bamboo turned into a carbon-fiber matrix, possibly with graphene/graphite layering).

**Thickness (diameter):** - **Original / new equivalent Shelby bulbs**: ~80 microns (0.08 mm) diameter. This was measured by laser diffraction on an identical new ~30 W Shelby bulb (Annapolis Naval Academy tests, 2008–2011) and confirmed by Sandia imaging. It is described as **eight times thicker** than a typical modern tungsten filament of the era. - **The actual Centennial bulb today** (originally rated ~60 W, now running at ~4 W): Thinned to ~48 microns diameter (24-micron radius) due to gradual evaporation over 125+ years. The carbon-fiber matrix was strong enough that it never broke despite material loss. - Cross-section: Originally square (from sheet cutting), then formed into a short, high-resistance coil/loop (~14.5 cm uncoiled length) optimized for downward light when hung base-up.

These traits (thick carbon filament + low operating temperature + vacuum or inert gas fill + high-quality hand-blown glass and platinum leads) are why it has outlasted virtually every other bulb. The filament runs much cooler and more robustly than thin tungsten designs, which fail faster from thermal shock and evaporation.

No one has disassembled the Centennial Light itself (it is treated as a fragile good-luck charm at the Livermore fire station), so all precise data comes from identical-vintage Shelby bulbs tested non-destructively. The “secret process” details died with Chaillet and the company, but the tests give the most exact physical specs available.