Electrodeless gas discharge lamp having flat induction coil and dual gas envelopes

An electrodeless gas discharge light assembly includes a lamp base (12) having a pair of light-transmitting lenses (14, 16) supported in axially opposed relation to one another. An electrodeless gas discharge light source (28) is mounted between the lenses (14, 16) and comprises a generally flat spiral induction coil (30) sandwiched between a pair of generally flat, planar envelopes (32, 34) in which an ionizable gas (46) is contained. Energizing the coil (30) inductively induces discharge illumination of the gas (46) causing light to be emitted in axially opposite directions through the lenses (14, 16) without obstruction by the coil (30).

BACKGROUND OF THE INVENTION
 1. Technical Field
 This invention relates generally to electrodeless gas discharge lamps and
 more particularly to the configuration and arrangement of the induction
 coil and the envelope in which the discharge gas is sealed.
 2. Related Prior Art
 Various arrangements for the induction coil and envelope of gas discharge
 lamps are known and generally involve locating the induction coil external
 of the envelope in closely adjacent relationship therewith. The envelope
 often has a generally cylindrical shape and is surrounded by a helically
 coiled induction wire. When energized, the coil excites the gas within the
 envelope to discharge illumination. The light which is emitted is blocked
 somewhat in the radial direction by the induction coil but not in the
 axial direction of the free end of the envelope. In many applications that
 employ this type of coil and envelope arrangement, the light is intended
 to be directed axially rather than radially and thus the blockage of light
 in the radial direction by the coil does not inhibit the performance of
 the light.
 In another known arrangement, a flat spiral induction coil is supported
 adjacent a flat envelope and the light which evolves is emitted forwardly
 of the envelope, but is blocked in the opposite axial direction by the
 presence of the coil on the backside of the envelope. In these known
 applications, such blockage of the light by the coil does not present a
 problem since the light is intended to be directed in the forward
 direction only.
 In other lighting applications, such as emergency flasher beacon lights of
 the type used, for example, on road construction pylons, barriers, signs
 and the like, the light is directed in opposite axial directions from a
 central incandescent light source through a pair of axially oppositely
 disposed lenses of the device. The incandescent lamp is often powered by a
 battery housed within a lamp base which mounts the incandescent lamp and
 lenses. Both the incandescent lamp and battery have a limited operating
 life, and as such the present emergency flasher beacons require periodic
 maintenance which adds cost and inconvenience to their usage.
 It would be desirable to replace the incandescent lamp source with an
 electrodeless gas discharge lamp source since it would eliminate the
 presence of an electrode (i.e., a filament) which is the principal cause
 for the failure of incandescent lamps. An electrodeless gas discharge lamp
 source would further draw far less power than a comparable incandescent
 lamp and its usage would prolong the operating life of the battery,
 minimizing or altogether eliminating the requirement for frequent
 maintenance associated with the known incandescent beacon flashers.
 There does not currently exist, however, an electrodeless gas discharge
 light source suitable for such a double-sided lighting application. In the
 case of the discharge lamps described above, the induction coil in each
 case would interfere with the emittance of light through at least one of
 the lenses and as such would impair the performance of the light.
 The present invention is directed at providing such an electrodeless gas
 discharge lighting configuration suitable for double-sided lighting
 applications.
 SUMMARY OF THE INVENTION AND ADVANTAGES
 An electrodeless gas discharge lamp assembly constructed according to the
 present invention includes a lamp base, a pair of light-transmitting
 lenses mounted on the base in axially opposed relation to one another, and
 is characterized by an electrodeless gas discharge illumination source
 including a generally flat spiral induction coil disposed between the
 lenses having axially opposite sides, and a pair of generally flat gas
 discharge envelopes disposed between the lenses on the opposite sides of
 the coil each having sealed therein an ionizable gas inductively excitable
 to discharge illumination by operation of the coil.
 Such an axially sandwiched arrangement of the coil and the two envelopes
 has the advantage of exciting the gas in both envelopes with a single
 coil, directing the light in axially opposite directions without
 obstruction from the coil. While not limited in its application, the
 invention is particularly well suited for emergency flasher or beacon-type
 lights wherein the light from the central source is transmitted in a)dally
 opposite directions through the opposed lenses of the device. The
 electrodeless gas discharge light source has the further advantage over
 conventional incandescent lamp sources of minimizing or all together
 eliminating the need to periodically replace the light source and
 prolonging the life of the battery of such assemblies by operating at a
 relatively lower rate of energy consumption.

DETAILED DESCRIPTION
 An electrodeless gas discharge lamp assembly constructed according to a
 presently preferred embodiment of the invention is indicated generally at
 10 in the drawings and comprises a lamp base 12 mounting a pair of
 light-transmitting lenses 14, 16 supported in axially opposite relation to
 one another defining a space 17 therebetween. The lenses 16 are generally
 flat and planar, although they may be bowed somewhat convexly away from
 one another as illustrated in FIG. 2. The lenses 16 lie in parallel planes
 and are aligned along a central axis A of the assembly 10. The base 12 may
 have a ring 18 that preferably is circular on which the lenses 16, which
 are likewise preferably circular when view along the axis A as in FIG. 1,
 are mounted by means such as the screws 20 of FIG. 1 or by other suitable
 means, including clips, fasteners, adhesives, and the like.
 The light assembly 10 depicted in FIGS. 1 and 2 is preferably an emergency
 flasher or beacon light of the general type commonly used to mark
 barriers, pylons, signs, equipment and the like to gain the attention of
 those in the vicinity of the need to exercise caution.
 The base 12 has a housing 22 that may include separable upper and lower
 housing portions 23, 24 defining a cavity 25 within the housing. An
 on-board power source in the preferred form of one or more batteries 26 is
 supported with the cavity 25 of the housing 22 so as to be protected from
 the elements and to provide electrical power to the illumination source to
 be described below. The separable housing portions 23, 24 provide access
 to the cavity 25 and the contents therein.
 The lenses 14, 16 may be manufactured to include a light-diffusing pattern
 or features 27 provided across the surface thereof for diffusing the light
 transmitted through the lenses 14, 16 in predetermined manner to achieve
 the desired lighting characteristics.
 According to the invention, an electrodeless gas discharge lamp source 28
 is provided in the space 17 between the lenses 14, 16 for supplying light.
 The source 28 comprises a generally flat spiral induction coil 30 axially
 sandwiched between a pair of generally flat, planar light-transmitting
 envelopes 32, 34. As shown best in FIGS. 2 and 3, the coil 30 and
 envelopes 32, 34 are preferably united as a single, integrated subassembly
 wherein the coil 30 is sandwiched in fixed relation between the two
 envelopes 32, 34 and secured by means of a suitable adhesive or the like.
 The coil 30 has axially opposite sides 36, 38 with respect to the axis A.
 An inner surface 40 of the envelope 32 engages one side 36 of the coil,
 whereas an inner surface 42 of the other envelope 34 engages the opposite
 side 38 of the coil 30. The envelopes 32, 34 are preferably separate and
 distinct from one another each defining an enclosed space 44 in which an
 ionizable gas 46 is sealed and excitable to discharge illuminated when
 ionized by operation of the induction coil 30 according to known
 principals. Any of a number of ionizable gases suitable for electrodeless
 gas discharge lighting applications may be employed, including, for
 example, neon, xion, mercury, mixtures of these and/or others.
 The envelopes 32, 34 may be fabricated of quartz or the like suitable for
 transmitting light while retaining the gas 46 therein. The envelopes 32,
 34 preferably correspond in shape to that of the lenses 14, 16, and thus
 are preferably circular when viewed in the direction of the axis A. The
 envelopes 32, 34 are further preferably concentric with the lenses 14, 16
 and thus lie along the axis A.
 The coil 30 is coupled at its ends 48, 50 by lead wires 52, 54,
 respectively, to an induction circuit 56 supported within the base 12. The
 circuit 56 is, in turn, electrically coupled to the energy supply or
 batteries 26. The circuit 56 is operative to convert the power supplied by
 the batteries 26 to induce the induction coil 30 to emit high frequency
 energy signals which act on the gas 46 to ionize and excite the gas to
 discharge illumination. It is preferred that the circuit 56 and coil 30
 operation in the RF range such that the coil 30 emits RF signals to drive
 the gas 46. The principals of discharge illumination through high
 frequency induction signals are well know to those in the art and thus
 will not be elaborated upon here.
 As illustrated by the directional light rays L of FIG. 2, the light given
 off by the gas 46 in the envelopes 32, 34 will be directed outwardly
 through the lenses 14, 16 in axially opposite directions along the axis A
 without obstruction from the coil 30. In other words, by locating the coil
 30 axially between the envelopes 32, 34, there is a direct path for the
 light emitted from the envelopes 32, 34 to transmit through the lenses 14,
 16 without encountering the coil 30.
 As mentioned earlier, the assembly 10 of the drawings is preferably an
 emergency-type flasher. It is thus preferred that the circuit 56 include
 suitable flasher circuitry which would act to energize the coil 30 in
 timed pulses in order to produce corresponding timed illumination of the
 gas 40 to achieve the flashing effect. In other words, the circuit 56
 would operate to energize and then deenergize the coil in repeated timed
 cycles to achieve an on/off flashing of the light assembly 10.
 The assembly 10 may further include a high frequency barrier 58 in the
 preferred form of an RF screen surrounding the coil 30. The screen 58 is
 operative to permit the passage of light therethrough while blocking the
 transmission of the high frequency signals generated by the coil so as to
 contain them within the assembly 10. The screen 58 may be conveniently
 mounted along the inner surfaces of the lenses 14, 16 and may, for
 example, be adhered thereto.
 FIG. 4 shows an alternative embodiment of the invention wherein like
 features are represented by like reference numerals, but are offset by
 100. The base 112 and circuitry 156 are the same as that previously
 described. The principal difference is the elimination of the lenses 14,
 16 and the provision thereof of dual purpose envelopes 32, 34 which serve
 not only to contain the gas 46 but also serve as the lenses. In the
 illustration, the envelopes 132, 134 are generally flat and planar, yet
 are outwardly convex or bowed away from one another to take on a lens
 shape. The extent of bowing is exaggerated in the drawing figure for
 purposes of illustration. The coil 130 is supported between the envelopes
 132, 134 and serves as before to energize the gas 46 in both envelopes 32,
 34. The envelopes 132, 134 may be formed with light-refracting features 60
 which act to diffuse the light transmitted through the envelopes 132, 134
 to achieve a desired lighting characteristic.
 Obviously, many modifications and variation of the present invention are
 possible in light of the above teachings. It is, therefore, to be
 understood that within the scope of the appended claims, the invention may
 be practiced otherwise than as specifically described. The invention is
 defined by the claims.