CONGRESSES AND CONFERENCES

CONFERENCE ON NEW LIGHT SOURCES

G. V. Spivak and B. N. Klyarfel’d

From November 25 to 27, 1933, a conference of a number of laboratories working in the field of the physics and technology of new light sources was held at the All-Union Electrotechnical Institute in Moscow. The conference on these questions was convened for the first time and had as its aim the mutual exchange of experience and the coordination of work in the given field. The problem of new light sources is of great practical interest because the construction of a light source, convenient for operation and based on a gas discharge, will make it possible to obtain light several times more economically than in incandescent lamps. It is interesting to note that in this field the results of purely scientific work are closely connected with questions of the technology of new light sources. At the conference, which lasted 3 days, a number of reports were heard concerning physical questions and a number of questions connected with the improvement of already existing light sources.

The conference was opened by an introductory address by S. O. Maizel’ (VEI), who dwelt on those requirements which lighting engineering and operation impose on new light sources. The drawback hampering at present the introduction of gas-discharge tubes is, in view of their falling characteristic, the need for the series connection of a choke (additional resistance), which reduces the economy of the entire installation and, in the case of an alternating-current network, lowers the cos φ. A further drawback of some types of gas-discharge tubes is the difficulty in igniting such a light source, which requires the use of additional ignition devices. The speaker considers that the color of light sources cannot serve as an obstacle to their use for lighting streets, squares, and highways.

B. N. Klyarfel’d (VEI) reported to the conference on materials concerning the economy of luminescence, the brightness, and the gradient of potential in the positive column of an intense discharge in mercury vapor. A discharge in mercury vapor at high vapor pressures gives an economy of luminescence that increases with increasing pressure and increasing current strength and reaches more than 50 Lm/W. An ordinary incandescent lamp has an economy of the order of 12–17 Lm/W. In a number of curves the dependences of the electrical and luminous properties on the pressure of the mercury vapor, the current strength, and the diameter of the tubes used were given. Mercury discharge tubes possess a substantial advantage, expressed in the possibility of igniting them directly from a low-voltage alternating-current network, which is based on lowering the ignition potential in a tube filled with argon in the presence of mercury vapor (the Penning effect). At low temperatures, corresponding to street temperature in wintertime, owing to the small partial pressure of mercury vapor, the ignition potential of the tubes increases greatly and the ignition of a gas-discharge tube becomes difficult. The speaker pointed out some circuits tested at VEI which make it possible to eliminate this drawback.

N. A. Kaptsov reported on the results of the work of the electrovacuum plant laboratory on various questions connected with the technology of manufacturing gas-discharge tubes and with their structural design. A whole series of difficulties standing in the way of constructing a gas-discharge tube possessing

CONGRESSES AND CONFERENCES

…having a long lifetime and high luminous properties, poses to laboratories a number of scientific and technical problems concerning processes at electrodes, the electric and thermal regime of tubes, and questions of glass. At present, specimens of tubes have been obtained that burn for up to 1000–2000 hours. The speaker points in detail to a number of scientific questions whose solution is important for new light sources. Of very great significance is the elucidation of the conditions affecting the distribution of intensity in the spectra of various vapors and gases. It is necessary to clarify our ideas about the processes in the oxide cathode; the study of the heat balance of the discharge and the study of the cord discharge are essential. The question of the simultaneous excitation of mercury vapors and metallic impurities is important. It is necessary to seek ways of correcting the color of light sources. One possible such way is the method of fluorescence. Of great importance is also the study of the discharge in the vapors of sodium and other metals. For the introduction of gas-discharge tubes, the problems of igniting the discharge and of developing switching devices are of great importance.

N. N. Ermolinsky (VEI), in his report, points to the difficulties of calculating mirror fittings for light sources whose luminous body has the form of a line. By experimentally selecting the fittings, it was possible to obtain a highly satisfactory definite distribution of the luminous flux for a horizontally arranged gas-discharge tube. The speaker illustrates his communication with a number of diagrams.

D. V. Zernov (VEI) reported experimental and literary material on the luminescence of sodium vapor. A discharge tube with sodium vapor contains some inert gas which serves for igniting the discharge, and metallic sodium, the vapors of which begin to glow when the tube is heated. A considerable share of the energy consumed in the discharge goes into the radiation of the yellow resonance line of sodium, whose output to the exterior may, according to literature data, reach 95% of the energy supplied. Therefore sodium tubes are very important in the sense of achieving great economy in lighting. Depending on the pressure of the sodium vapor, the luminous efficiency first increases, reaches a maximum, and then begins to fall. The cause of the fall is the increase of processes leading to the quenching of resonance radiation. A low current density is favorable for the output of the yellow line, because at high current densities, through successive excitation, radiation of other lines of the sodium spectrum occurs. The speaker further dwells on the role of the kind of inert gas and its pressure, whose influence is manifested because of the difference in atomic weight, effective diameter, and the value of the first excitation potential.

M. M. Glagolev (GOI) dwelt on the role of the distribution of electron velocities in a gas discharge in the distribution of the intensity of spectral lines. An illustration of this is that in a tube containing neon and mercury vapor, in narrow parts of the column, where the electron “temperature” is higher, it is chiefly the neon that glows, the pressure of which exceeds the partial pressure of the mercury vapor many times over. In the wider parts of the tube, however, where the electron “temperature” is lower, the glow is due only to mercury vapor.

B. N. Klyarfeld presents experimental data on the dependence of the luminous efficiency, the potential gradient, and the brightness in the positive column of a neon discharge on the current, the diameter of the column, and the pressure of the neon. The regularities obtained are explained by the large role of excited atoms in the states \(S_2\), \(S_3\), \(S_4\), \(S_5\) (Paschen’s notation). The conditions for the greater stability of these states correspond to the highest luminous efficiency. Under optimal conditions, for a column diameter of 60 mm, a light output of 12 Lm W was observed.

On the phenomena near the oxide cathode in mercury vapor at low pressure, S. D. Gvozdover (Moscow State University, “Laboratory of Electrical Phenomena in Gases”) reported. The investigation was carried out by means of the probe method; moreover, by changing the heating of the probe, it was possible to trace…

with a change in the potential distribution near a negatively charged electrode placed in the discharge, and to trace the distribution of the current into ionic and electronic current. The report was illustrated by a number of curves.

A. M. Shmelev (VEI) reports on various types of modulated light sources used in television. These sources employ a concentrated discharge in neon, sodium, and mercury. The speaker points out a number of possibilities for obtaining high-brightness sources.

N. A. Kaptsov (MSU, Laboratory of Electron. Phen. in Gases) reports on work (together with V. V. Afanas’eva) on the study of transient stages in a gas discharge when the cathode temperature is raised. When the cathode is heated to the temperature of electron emission from it, the cathode fall rapidly decreases, and it is possible to observe all the transient stages. The work verifies the fact of such a fall and reveals the moment of such a fall of the potential in the cathode parts of the discharge during the transition from a glow discharge to an arc discharge.

Materials on the composition and mechanism of emission of oxide cathodes were presented by G. A. Tyagunov (Electrolamp Plant). At present there is no generally accepted theory of the phenomena on the oxide cathode, and therefore studies in this field are of considerable interest. The use of an oxide cathode in a gas-discharge tube imposes a number of specific requirements on the stability of the cathode under discharge conditions.

A. N. Terenin (GOI) dwelt on the possibilities of using molecular gases to obtain visible light in a discharge. The gas used must possess great chemical stability, a large heat of dissociation, and give, upon excitation, radiation lying in the visible region. Halides present inconveniences because of their ability to form negative ions with the electron. It is usually thought that inelastic losses of electron energy in molecular gases are caused by excitation of the vibrational energy of molecules. However, the probability of such a process is small, and basically inelastic losses are caused by dissociation of the gas molecule under electron impact. Certain possibilities are available when mixtures of a noble gas with a small amount of a molecular gas are excited. Thus, for example, helium and carbon dioxide give a light output of up to 15 Lm/W.

A. A. Novikov (GOI) reported on the application of the anomalous-dispersion method to determining the number of excited centers in a discharge and on preliminary materials obtained by this method in mercury vapor. In a discharge in mercury vapor at high pressure and high current densities, the application of this method encounters a number of difficulties. However, in many cases this method can yield very valuable results.

V. A. Fabrikant (VEI) reported on the determination of the intensities in the lines of the visible part of the mercury spectrum. The obtained materials, together with data for the course of the concentration of individual levels of excited mercury atoms—with current strength and pressure, measured by the absorption method—indicate the great role of successive excitation in an intense mercury discharge. The speaker dwelt on further possibilities for increasing the economy of the mercury discharge.

S. E. Frish (GOI) drew attention to the possibilities afforded by collisions of the second kind, through excitation of definite lines of admixed gases. Other possibilities for redistributing the energy over the spectrum are afforded by choosing the cathode potential gradient, for example in a discharge with a hollow cathode, so that the presence in nitrogen of small impurities of argon can be determined, which would be impossible in an ordinary positive column of the discharge.

A report on the very important questions of glass for gas-discharge tubes was delivered by F. P. Oshchipkov (Electrolamp Plant), and a communication by Shkol’nikov (Glass Institute). It was reported on the difficulties that stand in the way of creating stable glasses, easily soldered with metals, for tubes with metal vapors. The speakers reported on experiments carried out

on the welding of various types of glass, and demonstrated samples of tubes resistant to the action of sodium vapor.

S. K. Moralev (Moscow State University, Laboratory of Electrical Phenomena in Gases) spoke about measurements of ignition potentials as a function of \(pd\) for pure argon. He also attempts a theoretical accounting of the observed changes in ignition potentials in the presence of impurities, by taking into account changes in the ionization coefficient entering Townsend’s equation.

Saburenkov (LETI) reported on news from the patent literature and noted the inadequacy of the use of these materials by those working in the field of new light sources.

Semenovskaya (Psychotechnical Institute) reported on measurements of visual acuity carried out in neon and mercury-discharge light. At the conclusion of the conference, a joint discussion of the plans for 1934 was held and a resolution was adopted, which noted the necessity of further intensive development of theoretical and technical work in the field of gas discharge.