Photographic Use of Electrical Discharge Flashtubes

TLDR

Xenon-filled discharge flashtubes convert stored electrical energy into light with about 40 lumens per watt, offering daylight‑like spectral output that remains stable across voltage and usage, making them valuable for visual and photographic applications. The authors propose using the flashtube as a standard lamp for flash comparison. The study describes a method to measure integrated light output, typical circuits, and provides an approximate formula linking condenser energy, reflector type, and film speed to the photographic exposure factor. Measured data show that the FT‑14 flashtube’s light output and efficiency vary predictably with stored energy, allowing accurate prediction of light quantity from capacitor energy.

Abstract

Xenon-filled gaseous discharge tubes flashed from energy stored in electrical capacitors are very useful converters of electrical energy into light, for both visual and photographic purposes. The efficiency for a typical tube is about 40 lumens per watt for rated conditions. Measured values of light output and efficiency as functions of energy input are given for the FT-14 flashtube. A method of measuring the integrated light output is described, as well as typical circuits and electrical conditions. The xenon electrical flashtube is particularly useful for color photography since its spectral distribution is similar to that of daylight and since the spectral distribution and efficiency are not appreciably affected by voltage or life. The quantity of light is predictable in terms of energy input from the storage capacitor. The flashtube is proposed as a standard lamp, especially for flash comparison. An approximate relationship useful for calculating the photographic exposure factor or guide factor (distance × aperture) is given in terms of energy in the condenser, the type of reflector used, and film speed.