Why is a tungsten incandescent lamp at most ~5-6% efficient? We derive the visible radiant efficiency of thermal light from Landauer's principle: every photon emission cycle pays a toll of alpha^-1 ~ 137 irreversible bit-erasures, each costing kT ln 2. The resulting channel-counting expression eta = nᵥal / (nᵥal + alpha^-1 ln 2) gives etaW = 5. 94% for tungsten (nᵥal = 6), matching the observed radiometric scale. A three-stage emission model (quark / proton / electron sectors) predicts documented inflection points in the emissivity curve. This v2 revision: (i) removes the Allen-Dynes lattice-buffer correction in Section 6 (empirical testing across 15 metals showed no systematic preference) ; (ii) adds prediction (f) in Section 10, an equal-valence falsification test for Mo vs. W (both nᵥal = 6, coincident predicted eta) ; (iii) updates the companion-paper reference to the concept DOI 10. 5281/zenodo. 19446942 and notes the 246-bit vacuum-ADC cosmology extension in Paper XIV. Not peer reviewed. Prepared with the assistance of artificial intelligence.
Alexander Nachtigall (Tue,) studied this question.