Abstract: A light source, particularly suited for surgical and other medical illumination applications, includes an electrodeless lamp assembly, a reflector having the electrodeless lamp assembly mounted therein and high frequency power source for supplying high frequency power to the electrodeless lamp assembly. The electrodeless lamp assembly includes an electrodeless high intensity discharge lamp capsule including a light transmissive discharge envelope enclosing a discharge volume containing a mixture of starting gas and chemical dopant material excitable by high frequency power to a state of luminous emission. The luminous emission has a color rendering index greater than 85 and preferably has a color rendering index greater than 90. The luminous emission preferably has low energy in the spectral range of 800 to 1000 nanometers relative to energy in the visible spectral range.

Abstract: Ignition of an electrodeless lamp, energized by microwave or radio frequency energy, is achieved by disposing a ferroelectric igniter in the lamp envelope along with the fill material. The igniter responds to switching of its spontaneous ferroelectric polarization by emitting electrons that collide with the atoms of the fill material to discharge further electrons and ultimately provide emission of light. In the preferred embodiment, the microwave or radio frequency energy used to excite the fill material is applied to the ferroelectric igniter to cause switching of its spontaneous ferroelectric polarization. Another preferred feature is the securing of the igniter, in the form of a thin patch or wafer, to the inside surface of the lamp envelope in a generally perpendicular orientation to the electric field in the microwave excitation energy.

Abstract: An electrodeless lamp capsule includes a light-transmissive discharge envelope enclosing a discharge volume containing a mixture of starting gas and chemical dopant material excitable by high frequency power to a state of luminous emission, and a lamp stem attached to the discharge envelope. The lamp stem includes a first section having a first cross-sectional area and a second section attached to the discharge envelope. The second section of the lamp stem has a second cross-sectional area that is less than the first cross-sectional area. The lamp stem may be a tube having a longitudinal slot which defines spaced-apart, first and second elements that are attached to the discharge envelope. The first and second elements have a relatively small total cross-sectional area for conducting heat from the discharge envelope and permit secure attachment of the lamp stem to the discharge envelope.

Abstract: An electrodeless light bulb assembly including a case or housing supporting an electrodeless light bulb as well as a convection type heat exchanger. A solid state RF driver circuit is located inside the housing and connects to an excitation coil wrapped around the light bulb. The excitation coil comprises a metal heat pipe so as to provide an efficient thermal transport mechanism for the heat generated by the coil and the heat radiated thereto from the electrodeless bulb to the heat exchanger in addition to generating an RF excitation field for the electrodeless light bulb.

Abstract: An excitation circuit for an electrodeless light bulb which includes an RF source, a driver amplifier, and a load matching network and where the frequency of the RF energy generated by the source is swept over a predetermined frequency range in a controlled manner by a programmable frequency controller to cover the entire range of possible load match tuning conditions so that the electrodeless bulb will be substantially matched at all times to the source at some frequency in the sweep range.

Abstract: EMI suppression in electrodeless discharge lamps by inward RF-reflectance from the enclosure walls (12) of 90%+ and use of an absorber (16) of RF power having an absorption coefficient greater than 40%, a transmission coefficient less than e.sup.-3, and an effective area facing the interior of the enclosure between 5% and 40% of the area of the RF-reflective light transmissive enclosure.

Abstract: An electric lamp assembly includes an electrodeless lamp having a closed-loop, tubular envelope enclosing mercury vapor and a buffer gas at a pressure less than about 0.5 torr, a transformer core disposed around the lamp envelope, an input winding disposed on the transformer core and a radio frequency power source coupled to the input winding. The radio frequency source supplies sufficient radio frequency energy to the mercury vapor and the buffer gas to produce in the lamp envelope a discharge having a discharge current equal to or greater than about 2 amperes. The electrodeless lamp preferably includes a phosphor on an inside surface of the lamp envelope for emitting radiation in a predetermined wavelength range in response to ultraviolet radiation emitted by the discharge.

Abstract: A sulfur, selenium, and/or tellurium based lamp for providing visible light. The lamp is operated in a regime for providing high efficacy wherein the ratio of the volume to surface area of the bulb is greater than 0.45 cm, the concentration of the sulfur, selenium, or tellurium is less than 1.75 mg/cc, and the power density is between about 100 watts/cc and 5 watts/cc.

Abstract: A cold-cathode, crossed field switch has a magnet system which generates a magnetic field that is radially-oriented about a switch axis and a planar electrode system which generates an axially-oriented electric field. These structures facilitate a switch whose capacitance, inductance and fabrication costs are all reduced from that of conventional cold-cathode, crossed-field switches. Magnets of the magnet system are arranged in two concentric annular rings with their north and south poles aligned either axially or radially. The planar electrode system includes a cathode, a source grid, a control grid and an anode which are arranged in a substantially parallel relationship.

Abstract: A high intensity discharge lamp without mercury is disclosed radiating a selected spectrum of which can be almost entirely in the visible range from an envelope that contains a sulfur containing substance. The lamp utilizes a signal source that generates an excitation signal that is externally coupled to the exterior surface of the envelope to excite the enclosed sulfur containing substance. Various embodiments of the lamp use electrodes adjacent the envelope to couple the excitation signal thereto with the face of the electrodes shaped to complement the shape of the exterior surface of the envelope. Two shapes discussed are spherical and cylindrical. To minimize filamentary discharges each envelope may include an elongated stem affixed to the exterior thereof whereby a rotational subsystem spins the envelope.

Abstract: An electrodeless lamp assembly includes an electrodeless lamp capsule, a substrate having top and bottom surfaces and an edge, an applicator for coupling electrical energy to the lamp capsule and a refractory support block. The support block includes a top wall having a recess and a side wall having a groove. The lamp capsule is affixed in the recess, and the edge of the substrate is secured in the groove. The lamp capsule is supported above the substrate by the support block. During assembly, the support block may be moved along the edge of the substrate, and the lamp capsule may be moved with respect to the support block to adjust the position of the lamp capsule.

Abstract: A low-pressure discharge lamp, in particular a deuterium lamp, including a cylindrically symmetric partition unit which forms two hollow spaces at each of the sides of the discharge lamp. Both hollow spaces are connected through an opening in the partition unit, which confines the plasma generated by a high-frequency electromagnetic field to pass through the opening to increase the intensity of the emitted radiation. Both sides of the cylindrically symmetric partition unit are provided with a hermetic seal, at least one of which sides is a radiation emission window. The generation of the electromagnetic field takes place capacitatively through electrodes located on the sides of the discharge lamp. At least one of the electrodes is disposed on the radiation emission exit window and has an opening for the radiation to exit.

Abstract: A line marker including hollow shell halves assembled about an elevated line and luminous tubes mounted on the shell halves illuminated by the electric field extending about the power line and without electrical connection with the power line itself.

Abstract: An electrodeless fluorescent lamp having a lamp envelope with an inner phosphor coating and containing a fill capable of sustaining a discharge when suitably excited by an electric field includes an electrically conductive coating on the exterior of the lamp envelope. The electrically conductive coating is also light transmissive and is effective for confining the electric field to within the lamp envelope.

Abstract: A discharge vessel (10) closed in a gastight manner has a cavity (11) enclosing a discharge space provided with an ionizable filling. A coil (20) with a winding (21) of an electric conductor and an assembly (30) of a heat conductor (31) and one or several elongate cores (32) of soft-magnetic material are accommodated in the cavity. The cores (32) are arranged along a longitudinal axis (33) of the heat conductor (31) in one or several recesses (34) of the heat conductor which issue into a circumferential surface (36) of the assembly (30). The heat conductor (31) occupies at least half the circumference in a cross-section perpendicular to the longitudinal axis (33) of the assembly (30). The construction of the lamp according to the invention renders possible lamp operation at higher lamp powers also without the use of a heat pipe.

Abstract: A low-pressure discharge lamp, in particular a deuterium lamp, includes a lamp envelope in which a plasma for generating UV radiation is formed by the capacitative generation of a high-frequency electromagnetic field. At least two partitions having openings are provided, wherein the openings are disposed on a common optical axis. The openings serve to constrict the plasma contained within the discharge vessel, which provides a high radial intensity of the plasma with high radiation stability for directing radiation along the optical axis. The radiation exits through a radiation emission window which is pervious to UV rays or through two exit windows placed opposite each other along the optical axis. The discharge lamp is particularly suitable for analytic measuring tasks, for example, as a light source in spectrophotometers.

Abstract: An apparatus which couples microwave energy to an electrodeless lamp. A source of microwave energy is connected to a wave guide having a slot along one wall thereof. A nominally cylindrical cavity enclosing an electrodeless lamp is closed at one end and coupled at a second end to the slot. The nominally cylindrical cavity has a non cylindrical surface portion which increases coupling from said slot to a second resonant mode which is orthogonal to a first primary resonant mode, creating a high amplitude standing wave in the region of the electrodeless lamp. Once ignition of the lamp occurs, the impedance of the lamp decreases significantly, and most of the microwave power for sustaining illumination is coupled to the electrodeless lamp in the first resonant mode producing a substantially matched load to said microwave source.

Abstract: An electrodeless fluorescent lamp includes a feedthrough structure extending from the exterior to the interior of the lamp which is constructed of a suitable material, e.g., platinum or a combination of platinum and rhodium, for directly connecting an interior EMI shield to ground. The feedthrough is also suitable for supporting an amalgam flag.

Abstract: For a given lamp size and lumen power, an electrodeless fluorescent lamp is configured with a split excitation coil and a baffle structure to provide multiple discharges, resulting in a higher light output and higher luminous efficacy.

Abstract: An electrodeless discharge lamp includes a single type auxiliary electrode for preliminary discharging, disposed on or adjacent to outer peripheral wall of lamp tube at a position for being electrostatically coupled to interior space of the tube, and supplied with a power from a second high frequency power source other than a first high frequency power source supplying a high frequency power to a main induction coil on the tube, whereby the lamp is made to attain an excellent startability without requiring any large size high frequency power source.

Abstract: An electrodeless fluorescent lamp and fixture is disclosed which operates at radio frequencies and contains a bifilar coil to reduce RF voltage between the plasma and the coil and a metallic cylinder (10) to remove heat from a said bifilar coil. The bifilar coil consists of two windings. The primary (induction) winding (6) is used to generate RF electrical azimuthal field in the bulb volume needed to maintain the inductively-coupled RF plasma. The second (bifilar) winding (18) has essentially the same number of turns and is wound on the inductive winding (6), but in the direction opposite to that of the primary (inductive) winding. The RF current flowing in the inductive winding (6) induces an RF voltage of the opposite polarity in the bifilar winding (18), so two adjacent turns of both windings have equal (or nearly equal) but of opposite sign RF potentials with respect to the plasma.

Abstract: A reflector fluorescent lamp with a reflective layer between the light-transmissive envelope and the phosphor layer(s). The reflective layer has a coating weight of at least 5, more preferably 6-8, mg/cm.sup.2 and is a blend of gamma alumina and alpha alumina, preferably 7-80 weight percent gamma alumina and 20-93 weight percent alpha alumina, more preferably 30-40 weight percent gamma alumina and 60-70 weight percent alpha alumina. The reflective layer finds particular utility in an electrodeless fluorescent lamp.

Abstract: An apparatus and method for operating an arc discharge lamp which can be hot restarted is described. The method involves providing low microwave power after the lamp ballast is disconnected from the lamp. The microwave power is modulated such that conductivity is maintained within the lamp as the lamp cools. Restarting the lamp is accomplished by reconnecting the ballast at any time. In one embodiment, the apparatus of the invention includes an arc discharge lamp and ballast coupled together with a switch to turn the lamp on and off. A microwave power supply is connected in parallel with the ballast and is coupled to the lamp when the ballast is shut off. The invention allows for hot restart of the arc lamp without requiring a high voltage pulse.

Abstract: An electrodeless, low pressure gas discharge lamp includes a vitreous envelope containing a discharge medium and being shaped with an external chamber for receiving an electrical excitation circuit. The excitation circuit is effective for exciting the discharge medium to emit light with electromagnetic fields that are generated by the excitation circuit. A circuit is included for supplying electrical power from power mains to the excitation circuit. A transparent, electrically conductive coating is provided atop the vitreous envelope and is electrically connected substantially directly to one of the power mains at any given time. A transparent, electrically insulative coating is disposed atop the electrically conductive coating, and comprises a contiguous, inorganic glass layer. The insulative coating preferably has a minimum coating thickness of at least about 3.1 microns.

Abstract: An excimer lamp utilizing a high pressure fill. The fill includes a halogen at an operating pressure of greater than about 350 torr or the combination of a halogen and a rare gas at a total operating pressure of greater than about 2.5 atmospheres.

Abstract: An electrodeless neon discharge light source having a red color light output is provided for use in automotive applications. The light source has a lamp envelope containing a fill of neon gas which, when excited to a discharge state by introduction of an operating signal over a tuned circuit consisting of a resonant capacitor and a ferrite coil, produces a red color light output. A flash control input to a ballast circuit arrangement provides the ability to control the light output using bursts of high frequency sinusoidal energy. The use of the burst signal approach allows for providing varying levels of light intensity output thereby signifying the distinction between braking conditions and an on condition of the tail light. Furthermore, by controlling the rate of flashing of the light source, an indication of a hard braking or emergency condition, could be conveyed.

Abstract: An illumination unit according to the invention comprises an electrodeless low-pressure discharge lamp 10. The illumination unit is provided with a lamp vessel 20 which encloses a discharge space 21 which contains an ionizable filling. The illumination unit is in addition provided with a holder 60 for the lamp vessel 20, with a coil 30 for generating a high-frequency magnetic field so as to maintain an electric discharge in the discharge space 21, and with a high-frequency supply 50 for the coil. The illumination unit is further provided with ignition aids 40 for promoting the initiation of the discharge.

Abstract: A lighting unit according to the invention comprises an electrodeless low-pressure discharge lamp 20 provided with a discharge vessel 20 enclosing a discharge space 20 with an ionizable filling in a gastight manner. The discharge vessel 20 has a recessed portion 23 and an enveloping portion 23 which transmits radiation generated in the discharge vessel. Means are present in the recessed portion for initiating and maintaining an electric discharge in the discharge space. The means comprise a member for generating an electric field in the discharge space. The recessed portion is provided with a luminescent layer, which is subdivided into mutually separated regions, at a surface facing the discharge space. The lighting unit further comprises a supply unit for supplying the means. The lamp of the lighting unit according to the invention has a comparatively low ignition voltage.

Abstract: A switching apparatus obtains a large switching current by multiplying the number of electrons emitted by field emission from a cold cathode. The switching apparatus is driven by an optical wave and includes a recess portion of an insulation layer formed on a silicon substrate, a cold cathode formed on the insulation layer comprising many comb-tooth like tips extending from one side above the recess portion, a gate electrode disposed on the recess portion on the side of the cold cathode, an anode formed on the insulation layer and extending from another side opposed facing to the one side above the recess portion, an optically transparent sealing member comprising a recess portion on its under surface for enclosing a dilute nitrogen gas in a vacuum space, and a semiconductor laser, supported on the sealing member by a support member, for irradiating a laser beam through the sealing member into the space.

Abstract: A plasma switch is provided which can limit fault currents to a range that is elecrostatically interruptible by a control grid. The switch includes magnets that generate a first magnetic vector which cooperates with an electric field to generate a plasma, the density of which is a function of the magnitude of the first magnetic vector. A stalling coil is arranged to generate a second magnetic vector that opposes and cancels a portion of the first magnetic vector in response to a fault current through the switch. This establishes a stalling condition in which the plasma density falls and a plasma potential gradient is set up in the switch. In this unstable condition, the plasma current is interruptible by the control grid.

Abstract: Apparatus for efficiently exciting an electrodeless lamp to produce visible light. A source of microwave energy is coupled to a cylindrical cavity which encloses an electrodeless lamp. The cylindrical cavity includes a sidewall and end wall which is made from a metallic mesh which passes light produced from the electrodeless lamp. The electric field intensity within the cylindrical cavity is increased in the region above the lamp center. The increased electric field intensity produces a more uniform temperature across the bulb service, increasing the rate of plasma heating of gas molecules in the lamp.

Abstract: A fluorescent lamp for use in special applications includes an electrodeless envelope of glass or other light transmissive material carrying fluorescent material within the envelope. An RF energy source and coupler are embedded in epoxy as an integral power unit, thereby isolating the power unit from the hazardous environment. The power unit and the envelope are shaped in complementary form such that the coupler and envelope are in energy-transfer relation to excite the lamp, but the envelope may be removed from the power unit to re-lamp the fixture.

Abstract: The present invention provides an arc lamp for producing a high intensity point source of light by magnetically compressing the light emitting element of the arc lamp. Arc lamp point light source 30 includes bulb 32 having two electrode 34, 36 spaced apart to have gap 35 therebetween and hermetically sealed within bulb envelope 44 filled with ionizing gas. Connector 46 is provided for applying a voltage potential across electrodes 34, 36 causing electric current to pass therebetween to generate arc plasma 42. Annular magnet 48 and bar magnet 50 located outboard of bulb envelope 44 generate a magnetic field around arc plasma 42 to compress the volume thereof between electrodes 34, 36.

Abstract: A high intensity discharge light source that uses a pseudo-random sequence generator to modulate an RF drive signal, and reduce electromagnetic interference (EMI) produced by the light source. The light source includes a high intensity RF discharge lamp, control and RF drive electronics that are coupled between a power source and the lamp. The control and drive electronics include an electromagnetic interference filter, and a regulator that outputs a bias voltage. The drive electronics provide RF power to the lamp, and includes an oscillator, a mixer/modulator, an amplifier, and an impedance matching network. The control circuit includes a pseudo-random sequence generator that generates a pseudo-random sequence of pulses to modulate the mixer/modulator and thus the output of the oscillator to thereby reduce the EMI spectral density generated in driving the RF discharge lamp.

Abstract: A high impedance plasma opening switch having an anode and a cathode and at least one additional electrode placed between the anode and cathode. The presence of the additional electrodes leads to the creation of additional plasma gaps which are in series, increasing the net impedance of the switch. An equivalent effect can be obtained by using two or more conventional plasma switches with their plasma gaps wired in series. Higher impedance switches can provide high current and voltage to higher impedance loads such as plasma radiation sources.

Abstract: A first portion of a spiral wire support for an amalgam is securely fitted into an exhaust tube formed in a re-entrant cavity of an electrodeless fluorescent lamp before attachment and sealing of the re-entrant cavity to the bulb of the lamp. A second portion of the spiral wire support extends into the bulb and holds an amalgam in thermal contact with the apex of the bulb. The second portion has a larger diameter than the first portion to ensure against movement of the spiral wire support into the exhaust tube. The end of the second portion of the spiral wire support is wetted with an alloy capable of forming an amalgam with mercury prior to insertion of the wire support into the exhaust tube. Mercury is added to the bulb after final evacuation of the bulb in preparation for dosing the lamp with its fill. As a result, an amalgam is formed and maintained in thermal contact with the apex of the bulb, regardless of lamp orientation.

Abstract: A simple and effective technique for reducing an external magnet flux emitted from a driven inductor surrounded by an ionizable gaseous medium. This technique includes surrounding the inductor with at least one shielding conductive loop, terminating the shielding loop in a capacitive termination to resonate, and maintaining a resonant frequency of the capacitive termination in series with an inductance of the shielding loop below the predetermined driving frequency of the inductor.

Abstract: A solar-powered, illuminated aircraft warning marker for connection to suspended cables and overhead transmission lines includes a polygonal housing having a plurality of light elements attached to different sides of the housing. The warning marker includes solar cells, storage batteries and electrical circuit apparatus for selectively illuminating the light elements during low ambient light and nighttime conditions.

Abstract: A push-pull Class E amplifier is used to provide an efficient transfer of power to the induction coil in an electrodeless discharge lamp and to reduce the amount of radio frequency interference emitted by the lamp into the surrounding environment. A bifilar or other type of multifilar induction coil, preferably center-tapped, is used to further reduce the radio frequency interference problem.

Abstract: Apparatus for exciting electrodeless lamps. A magnetron for generating electromagnetic energy in the microwave region includes an extension for its antenna terminal. The extension extends the length of the antenna to control the phase of loading on the magnetron. A circular ground flange and perforated screen enclose the electrodeless lamp, permitting microwave energy to excite the gas within the lamp, while confining the energy to the space bounded by the perforated screen and cylindrical ground flange. The extension for the antenna has a length which maintains the reflection coefficient phase to a level which does not adversely disturb the magnetron operating frequency.

Abstract: An excimer lamp utilizing a high pressure fill. The fill includes a halogen at an operating pressure of greater than about 350 torr or the combination of a halogen and a rare gas at a total operating pressure of greater than about 2.5 atmospheres.

Abstract: A glass rod extending through and sealed to the exhaust tube of an electrodeless SEF fluorescent discharge lamp has a metal support member at one end thereof for supporting an amalgam at or near the apex of the lamp envelope. The metal support member may comprise a spiral-shaped wire, a wire screen, or a wire basket. Preferably, the amalgam is maintained in contact with the apex of the lamp envelope. If desired, the metal support member may comprise a magnetic material to allow for magnetic transport of the amalgam assembly during lamp processing. The metal support member restricts spreading of the amalgam when in a liquid state; and the glass rod provides rigid support for the amalgam independent of lamp orientation.

Abstract: An electrodeless high intensity discharge lamp includes a lamp capsule containing a fill material for emitting radiation upon excitation by high frequency electromagnetic energy, a plurality of applicators spaced around a lamp capsule for nonresonant coupling of high frequency energy to the lamp capsule, a high frequency source for supplying high frequency power, and a power splitter and phase shifter for coupling high frequency power from the source to the applicators such that an electric field applied to the lamp capsule rotates at the frequency of the source. The applied high frequency energy is distributed over the lamp capsule so that the tendency for lamp envelope hot spots is reduced. Preferably, four helical couplers are spaced at 90.degree. intervals around the lamp capsule. The high frequency power applied to adjacent applicators is shifted in phase by 90.degree..

Abstract: An electrode-less high pressure discharge lamp has a lamp vessel which is surrounded by an electric coil having turns. End portions of the coil are electrically connected to current conductors. The turns of the coil are supported by aluminium nitride, which is in thermal contact with the current conductors. There is a good heat transfer from the coil to the conductors, keeping the coil relatively cool and efficient. The coil screens the lamp vessel to a small extent only, thereby improving the lamp efficacy.

Abstract: An electrodeless lamp which operates with a high efficiency and with a lower cooling requirement. The bulb is rotated at a high speed which results in a substantial increase in efficiency. Because more of the input energy is converted to light, and less to heat, the pressure of the cooling fluid source may be reduced, resulting in a less noisy system.

Abstract: A thyratron has an auxiliary "keep-alive" electrode in the form of a surface element with at least one aperture therein. In a preferred embodiment, the auxiliary electrode is disposed adjacent the upper end of a heat shield surrounding the cathode of the thyratron and is preferably coplanar with the upper end of the heat shield. A baffle can also be provided between the auxiliary electrode and the cathode to enhance control of the thyratron's switching action.

Abstract: Silver metal and nickel silicide are added to the fill of an electrodeless high intensity metal halide discharge lamp, which includes at least one metal iodide as a fill ingredient, for controlling the iodine vapor level therein. The nickel silicide acts to getter oxygen which has been introduced into the arc tube during lamp processing, thereby avoiding oxidation of the metal iodide portion of the fill and a concomitant release of free iodine into the arc tube. The silver acts to getter free iodine available from the metal iodide(s) of the fill as metal diffuses into the quartz arc tube wall, forming silver iodide (AgI). The combination of silver and nickel silicide acts to control the iodine level below an arc instability threshold to promote and maintain arc stability. In addition, neither silver nor nickel silicide attack the quartz arc tube wall. Lamp performance and lamp life are thus substantially improved.

Abstract: A plasma source for generating a plasma in a chamber in conjunction with a radio frequency generator is described. The plasma source comprises a coil spiral, at least one insulator and at least one capacitor. The coil spiral conducts the radio frequency wave from the radio frequency generator and induces a plasma in the chamber. It comprises at least two segments. Each insulator and capacitor couple two adjacent segments of the coil spiral together.

Abstract: An electrodeless SEF fluorescent discharge lamp of the type having an envelope with a re-entrant cavity formed therein for containing an excitation coil includes an amalgam positioned for maintaining an optimum mercury vapor pressure during lamp operation. An exhaust tube extending through the re-entrant cavity has an extension into the envelope toward the apex of the lamp envelope. The exhaust tube extension has a rim portion for holding an amalgam support in position within the lamp envelope. The amalgam support preferably comprises a wire wrapped about and held in place by the rim portion. At the other end of the wire, an amalgam is wetted to a wire screen or helical wire structure at a predetermined optimal location within the lamp envelope. Alternatively, two amalgams are supported by the amalgam support at predetermined optimal locations for starting and steady-state operation of the lamp, respectively.

Abstract: Disclosed is an electrodeless, low pressure gas discharge lamp. The lamp includes a vitreous envelope containing a metal vapor and an inert gas. The envelope is shaped with an external chamber for receiving an electrical excitation circuit. The excitation circuit is effective for exciting the metal vapor to emit light with electromagnetic fields that are passed through the vitreous envelope from outside, to inside, the envelope. A circuit supplies electrical power from power mains to the excitation circuit. A transparent, electrically conductive coating is disposed on the inner surface of the vitreous envelope for suppressing electromagnetic interference on the power mains. An electrically conductive coating is disposed on the outer surface of the vitreous envelope; it is capacitively coupled to the inner conductive coating, via a wall of the vitreous envelope, and is maintained at a suitable potential for suppressing electromagnetic interference on the power mains.