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J. Eur. Opt. Society-Rapid Publ. 22, 52( 2026)
( a)( b)
( c)( d)
Fig
. 3.( a) Irradiance maxima recorded for the same lamp at four different supply voltages;( b) normalized curves from( a) over the 650 V curve( black line);( c) values at specific wavelengths from( b) plotted vs. supply voltage;( d) SMR top = mid plotted vs. time, for four different supply voltages.
Table 1. For each device, maximum difference between measured norm. J sc and its linear regression( max. difference between solid and dotted line), and ΔJ sc = J sc @ 800 V − fit @ 800 V over J sc @ 800 V.
Fig. 4. Short-circuit current density, normalized over its initial value, versus the integrated irradiance( 350 – 950 nm). For each device, the solid curve represents the measured data, and the dotted curve represents the linear regression of the first two points of the curve.
Results in Section 3.2 report that when supply voltage is varied to adjust irradiance, spectra do not change, but those wavelengths appearing as dips in Figure 3b increase more slowly, and the higher-voltage spectra appear poorer of these spectral components. SMR @ 1 ms in Figure 3d decreases from 1.069 to 0.985 as supply voltage is decreased from 800 to 650 V, which gives a clear numerical value to quantify the effect.
The impact of supply voltage on measured I – V curves is depicted in Figure 4. These results compare the ideal behaviour where spectra increase coherently with supply voltage( dotted lines), and the real behaviour( solid lines) constituted by the actual measurements. The magnitude of this discrepancy is quantified by the“ Max nonlinearity” in Table 1, which is high for the“ Si PD” device since it includes a large number of dips in its large conversion range 850 – 1800 nm, and highest for the“ SJ bot” device, which conversion range 850 – 1800 nm extends further into the IR, beyond the spectrometer’ s range. These results suggest that further into IR, although not measurable, even more
Device |
Max nonlinearity |
ΔJ sc / J sc [%] |
SJ top |
−0.0117 |
−0.71 |
SJ bot |
−0.0406 |
−2.75 |
Si PD |
−0.0226 |
−1.75 |
dips might appear and strongly affect the“ SJ bot” current. Contrarily, being most of these dips in the 650 – 850 nm range, the“ SJ top” device is almost unaffected, as its sensitivity range 300 – 700 nm barely includes any dip.
Comparison between experimental results and those the device would have in ideal conditions, namely if all the spectral components would increase coherently with voltage, leads to the outcome that J sc is always underestimated, up to �2.75 %(“ SJ bot”).
5 Conclusion
Results in this work highlighted measurements artifacts that can impact indoor characterization, if not identified and considered. Temporal variation of spectral lines is not the same for every wavelength, but the discrepancy is acceptable for the first 1 ms of the discharge, where the fast I – V sweeps occur. Supply voltage, surprisingly, introduces 10 % inhomogeneity in lamp’ s spectral components when increased by just 50 V, and 20 % inhomogeneity when increased from 650 to 800 V. Consequently, irradiance does not scale linearly with supply voltage, as some spectral components are modified less than others. This yields to a