How much of the electrical input of a cesium, rubidium, potassium or sodium arc comes out as light between 0.4 and 1.3 µm. We traced every spectrum in a 1978 Xerox paper from the full-resolution scan. Pulsed sodium reaches 94% in band, pulsed cesium 60%, dc potassium 62%. Xenon at dc reaches 17%.
W. F. Hug, C. M. Hains, C. J. Marlett, “Spectra of alkali metal vapor and noble gas flashlamps,” J. Opt. Soc. Am. 68(1), 62–67 (1978). doi:10.1364/JOSA.68.000062
Lamps: 8 mm bore, 8 cm gap, sapphire or Lucalox envelope near 850 °C, 0.15 atm Ne start gas, alkali pressure set by a reservoir heater (alkali). Water-cooled quartz, 4–7 mm bore (Xe, Kr). measured spectra from the paper. digitized our trace and integrals. model the cell simulator.
η = ∫ S(λ) dλ over the plotted band, where S is radiant output per µm per unit electrical input (W/µm/W at dc, J/µm/J pulsed). digitized ±3%. Hover a row to load it on the bench below.
| Lamp | Mode | Best condition | η in band | Band µm |
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Put any of the 36 traced spectra (or a blackbody) on a stack of up to three photovoltaic cells. Each cell has its own band edge, edge sharpness, quantum efficiency, temperature and radiative efficiency. Hover a lamp or a cell material to preview it; click to keep it. The model runs as a 10 KB WebAssembly module. model
| Cell | Eg eV | edge nm | absorbs | Jsc A/cm² | Voc V | FF | P W/cm² |
|---|
Uses cell 1’s edge width, EQE, temperature and radiative efficiency, and the coupling settings above.
| Lamp | Fig. | Condition | η in band | Band µm |
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| Lamp | Figures | η each | band | spread |
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Data: lamps.json · lamps.csv. Every located marker and the traced curve on a 0.004 µm grid, with lamp metadata. Copied.
Calibration. From the full-resolution scan (3008 × 4320 per page). Each figure's axes are fitted to its own tick marks: about 130 px per 0.1 µm, residual under 1 px. That is ±0.001 µm and ±0.002 in spectral units.
Markers. Every plotted marker is located by normalized cross-correlation with templates learned from that figure's own markers. Each marker goes to its curve by shape (filled disk, open square, filled triangle, open diamond). Markers hidden under another curve's marker are shared. Three markers on the axis or fully covered were placed by hand from gridded close-ups.
Curves. The authors' drawn line is traced pixel by pixel between markers, following the ink, and integrated on a 0.002 µm grid. Where a curve runs hidden under another at its ends, it follows that curve. The cross-check table shows the result. The same dc 400 Torr lamp, traced independently from two or three figures, agrees within 0.3–4%. We quote ±3% on each integral.
What tracing cannot fix. The paper's sampling: interference filters every 330 Å from 0.41 to 0.71 µm and every ~500 Å above, each 120–300 Å wide. Self-reversed resonance lines between filters are only as resolved as the authors drew them. Every number is also a lower bound on total radiation. The data stop at 0.41 µm in the UV and at 1.1–1.28 µm in the IR. Pulsed Rb and K (Figs. 6 and 8) stop at 1.1 µm.
One cross-check from the paper. It says the 250 µs cesium spectra are about 25% above the 70 µs ones. Our integrals give 13–31% higher, depending on which current densities are paired.
Pulsed sodium at 94%. The dc 400 Torr reference curve is the same in Figs. 9 and 10 (36.1% vs 36.5%), so Fig. 10's doubled axis was read correctly. Energy balance makes 94% in band tight. The electrode falls take roughly 5–7% of a ~200 V, ~270 A arc, and the curve is still at 0.3 J/µm/J at 1.28 µm. The likely systematic is the paper's conversion from one detector reading to total output, which assumes a Lambertian cylinder (Wλ = 2π²d²Rλ). The paper validates that to ~5% for its alkali lamps. A realistic range is 70–94%. The 2.6× gain over the same lamp at dc does not depend on that calibration.
The cell model. Detailed balance, one ideal diode per cell. Each cell absorbs everything above its edge through a logistic edge of the set width, times its EQE. The dark current comes from reciprocity with that absorptance, divided by the external radiative efficiency (ERE). Cells in a stack are wired independently (four-terminal), highest gap on top. The band edge does not shift with temperature; set it directly. Preset EQE and ERE values are illustrative. Check: a 5778 K blackbody at 0.1 W/cm² on a 1.34 eV ideal cell gives 31.2%, the Shockley–Queisser value.