Brightness of a Capacitor Discharge Lamp - Bloch's Law for Brief Flashes

Brightness of a capacitor discharge lamp (tc, 16-25 micro sec) has been extrapolated from determinations of the subjective attenuation of comparable durations upon square wave flashes from a glow modulator tube (R1131C). For the large field (61 degrees) and high adaptation state (273 td), psychophysical integration of time and intensity (Bloch's Law) was found to hold only at durations less than 1.5 x 1000 microsec. Examination of the manufacturer's data on lamp candlepower converted to trolands encourages the conclusion that large errors occur when the troland and other photometric quantities remain uncorrected for Bloch's Law effects which are found at short durations. A correct troland or adequate troland is described.