442,307. Discharge lamps. CACHEMAILLE, A. S., Crown House, Aldwych, London.-(Universag Technische Akt.-Ges.; Glarus, Switzerland) Oct. 10, 1934, No. 29045. [A Specification was laid open to inspection under Sect. 91 of the Acts, April 15, 1935.] [Class 39 (i)] A " plasma " radiating visible or ultra-violet light is formed in a gas or vapour filled lighting space by one or more beams of primary electrons shot into the space from a source of slow electrons such as a hot cathode 14, Fig. 4, and this source is in communication with the lighting space through one or more openings 16<1> in a " plasma-filter " 16 of insulating material or of conducting material coated at the openings with insulation, the openings being so restricted in at least one direction perpendicular to the electron beams 16<2> passing through them that the current is limited by negative space and wall charges in the openings and is independent of excess electron emission by the electron source. The lamp operates at potentials of 50-300 volts without ballast or starting devices. Positive ions from the plasma entering the openings 16<1> are discharged on the walls of these openings and the plasma is thus prevented from spreading through the filter 16. Dimensions of the openings and operating data are specified. Round openings of diameter 8-1À1 mm. are referred to. Current entering the plasma as primary electrons 16<2> leaves it as slow-moving electrons of the plasma which flow to the anode in contact with the plasma. Efficiency is increased by using high currents and by choosing the gas pressure so that the energy of the primary electrons is transferred to plasma electrons electrostatically ; the linear dimensions of the lighting space, for example, of a pear-shaped or spherical bulb into which the primary electron beams are shot, are 5-50 times the mean free path of the primaries and the pressure is a few tenths of a mm. for helium and neon, a few hundredths for argon and metals of the third column of the periodic system such as mercury, and a few thousandths for alkaline metals. Neon gives an orangeyellow colour less red than its usual colour. White light can be obtained by mixtures of neon and mercury or of neon, sodium and cadmium. The hot cathode 14 may have oxide-coated dimples 17 and the electron beams may be accelerated by an apertured electrode 15 at a positive potential equal to or less than that of the anode of the lamp. In a modification, Fig. 5, a plasma filter 16 with many openings 16<1> is held directly on a flat cathode 18 above a heater 5 in a ceramic or metal case 11 and the anode of the lamp is a sleeve 12 outside the case 11. The cathode may be heated by an auxiliary discharge, Fig. 7 (not shown), and the plasma-filter may be curved so that the electron beams are convergent or divergent. In another modification, Fig. 6 (not shown), the electron source inside the case 11 is the plasma of an arc or glow discharge from an oxide coated cathode to an auxiliary anode which may be switched off after starting. In an alternating-current lamp, the cathode 18 and anode 12 are in halves operating on alternate half-waves, Figs. 11 and 12 (not shown), or each cathode is connected to an anode inside the casing 11 and facing large holes through the plasma-filter for the passage of plasma electrons, Figs. 13 and 14 (not shown). The anodes may be carbon coatings to reduce the danger of arcing. In a modified alternating- current lamp, Fig. 15, primary electrons from cathodes 60, 61 heated by a heater 62 emerge through slits 66 in the ceramic case 64 and plasma electrons flow through holes 68 to anodes 69 connected to the cathodes. Auxiliary anodes 70, 71 are connected to the cathodes through high resistances such as graphite coatings 72, 73. Two or more radiating plasmas may be connected in series ; the cathode 32, Fig. 10, is in communication with a plasma 38 through a filter 33 and the plasma 38 communicates with a plasma 39 through a filter 35 in a partition 34, the anode 36 with insulating lead 37 being in contact with the plasma 39.