CA2111426A1

CA2111426A1 - Electrodeless lamp bulb

Info

Publication number: CA2111426A1
Application number: CA 2111426
Authority: CA
Inventors: Alfred E. Feuersanger; Charles William Struck; William M. Keeffe; Michael J. Shea
Original assignee: Individual
Current assignee: Osram Sylvania Inc
Priority date: 1992-12-18
Filing date: 1993-12-14
Publication date: 1994-06-19
Also published as: EP0603014A1; DE69325349T2; EP0603014B1; DE69325349D1

Abstract

ABSTRACT

An improved bulb for an electrodeless lamp has a transparent envelope with a continuous wall and contains a chemical fill comprising an inert starting gas, mercury, alkali metal iodides, and a sufficient amount of scandium iodide and at least one iodide of a rare earth to increase the concentration of the rare earth in the vapor during lamp operation so as to enhance the color rendering index, Ra, of the lamp to a value greater than about 80 and result in a color temperature between about 3000 to about 5000 degrees Kelvin.

Description

ELECTRO~ELE5S LAMP BULB

CROSS REFERENCE TO RELATE:D APPLICATIONS

Application SPrial Number 07/845,285 filed March 3, 1992 to Shea et al and entitled Metal Iodide Lamp is a related application.

TECHNICAL FIELD OF TH~ INVENTION

This invention relates a lamp bulb for electrodeless lamps having a metal iodide fill with improved color rendering.
BACKGROUND OF THE INVENTION

High frequency electromagnetic field excitation of gas discharqes has been studied and applied for many years.
Originally, microwaves were applied in gas discharge devices such as Noise Sources, Transmit-Receive (TR) Tubes, and, : .
generally~ as Gas Discharge Circuit Elements. The :
interaction of microwaves with gas discharges was treated by S. C. Brown, Introduction to Elec~rical Di~charges in Qase~, John Wiley & Sons, Inc., New York, (1966). An early application to lamps is given in "Microwav Discharge Cavities Operating at 2450 MHz" by F. C. Fehsenfeld et al., Rev. Sci. Instruments, 36, No. 3, (March 1965), where,in a resonant discharge cavity power~ is transferred from ~he source to the lamp. The lamp is substantially enclosed by the resonant cavity impeding the transmission of ligh~ from the gas discharge source.

The first practical microwave light sources, often called electrodeless lamps, were described by a qroup at GTE
~aboratories in 1975. Using an electrodeless lamp and a D 92-1-103 P~TENT

termina~ion fixture, having an inner and outer conductor, lt is excited by high frequency power at 915 or 2450 MHz, or in the possible frequency range from 100 MHz ~o 300 GHz. This work is described and covered ln the following pa ents:
3,g42,058; ~,942,068; 3,943,401; 3,943,40~; 3,943,403;
3,943,404; 3,993,927; 3,995,195; 3,997,816; ~,001,631;
4,001,632; 4,002,944; ~,041,352; 4,053,814; 4,0~5,701;
4,070,603; 4,178,534; and 4,266,162.

The possible frequency bands available for microwave lamp operation are regulated by the Federal Communications Commission, Rules and Regulations, Vol. II, Part 18, Industrial, Scientific, and Medical Equipment, Federal Communication Commission, July 1981. See 18013, page 180.
Guidelines for threshold limit values for microwave radiation are published by the American Conference of Governmental Industrial Hygienists, Threshold Llmit Values and Biological Exposure Indices for 1989-1990; American Conference of Governmental Industrial Hygienists, Cincinnati, Ohio, pp. 108-111.

Microwave-powered lamps are comprised of a gas discharge in a sealed envelope containing a chemical fill of mercury, metal halides and starting gas, such as argon. The microwave power from a (solid sta~e, magnetron or other tub~) power source is coupled over a transmission line (e.g.
waveguide, coa~ial line or microstrip line). Impedance matching efficiently couples the EM-field into the chemical fill to start, develop, and maintain the dlscharge for efficient generation of light. The light emitting plasma discharge, the lamp fill, the arc tube and the ~ield coupler comprise the effective impedance matched load (field coupled lamp load) that the power supplying microwave transmission line sees.

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U.S. patent 4,427,921 to Proud et al de~cribes ~uch an application of high frequency power to an electrodele~ lamp containing metal iodide or iodine. Optical emi~sion is described as being dominated from excited iodlne atoms which emit ultraviola~ l.ight at 206.2 nm. Additional emissions are described as being produced in the visible and ultraviolet portions of the spectrum from radiative transitions in I, I2, HgI2, HgI, Cd, CdI2, CdI, etc., depending on the composition of the fill material.
U.S. patent 4,206,387 to Kramer et al descrlbes scandium iodide an~ sodium iodide chemical fills for an electrodeless lamp to provide high efficacy (about 100LPW) but only fair color rendering ~CRI=65~. As set forth, the use of raxe earth fills in electroded lamps result~ in "very high wall loadings ... resulting in a rapid decrease in color temperature ... and a very short eff ctive lifetime of about 200 hours." The improved electrod~less lamp, is set forth in column 6, lines 50 to 55, "mercury is needed for a high pressure discharge, argon is used to initiate the dischar~e, and a rare-earth halide is used to achieve atomic plus molecular emission." The result~ are described as being improved with the addition of cesium halide, but only mercury, argon, and a rare-earth halide are described as necessary. The improved fill includes a rare earth compound, i.e., dysprosium iodide, holmium iodide.

Because of their superior efficacy and operating life, conventional electroded lamps utilizlng a chemical fill of alkali and scandium iodides are highly desirable. GTE's Metalarc M100/U lamp, with a NaIScI3CsI chemistry, has a color rendering index (CRI) of 65, an initial lumen~ per watt (LPW) of 85, and a 10,000 hour lif~time. The above chemistry can be modified by the replacement of the element cesium with lithium to form a chemistry of NaIScI3LiI. The resulting lamp has an improved CRI of 73 while still .. ~ : - : - , : :~
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maintaining the 10,000 hour life and ~he 85 LPW ef~icacy.
However, a CRI of 73 must be further improved for tha excellent color rendering needed for showroom lighting, displays ln stores, and decorative illumination, both for indoor and outdoor use. Without such further improvement, their color rendering propertie~ limit their commercial use in certain color-critical applications.

Certain advantages are attendant with the electrodeless lamp, or microwave powered lamp as compared to the conventional electroded lamp. The absence of conduc~lon current electrodes/ i.e., the elimination of tungsten from the inside of the gas discharge tube, reduces significantly the limitations imposed by the high temperature chemical reactions of the active light producing lamp fill with the container and electrical lamp materials. The electrode feedthroughs (press seals) that can lead to lamp defects are also not required. In addition, lamp efficacy is improved, compared to equlvalent electroded lamps, by absence of the electrical and thermal conduction losses generated in lamps with conduction electro~es. Electrolysis of fill species, such as sodiuml is reduced to give good color stability.
The improved lamp performance may be more easily achieved without increase of wall temperatures.
These advantages, of themselves, do not improve the CRI
of electrodeless lamps. With rare earth fills they also do not allow low enough temperatures at the wall of the gas discharge tube to promote long life. Further improvement~
in chemical fills for high frequency microwave powered lamps are desirable, especially fills which desirably contribute to improved color rendering, superior efficacy, and longer operating life.

3S Certain terms as used in this specification have meanlngs which are generally accepted in the l~ghting ~ .. . . . - -- ~ . . - . -D 92-1-103 ~ PATENT

industry. The~e term~ are de~cribed in the IES LIGHTING
HANDBOOK, Reference Volume, 1984, Illuminating Engineering Society of North America. The color renderin~ index of light source (CRI) is a measure of the degree of color shift objects undergo when illuminated by the light source as compared with the color of those same ob~ects when illuminated by a reference source of comparable color temperature. The CRI rating consists of a General Index, Ra~ based on a set of eight test-color ~amples that have been found adequate to cover the color gamut. The color appearance of a lamp is described by its chromaticity coordinates which can be calculated from the spectral power distrlbution according to standard methods. See CIE, Method of Measurinq and SPecifyinq Colour Renderin~ Properties of Light Sources (2nd ed.), Publ. CIE No. 13.2 (TC-3,2~, Bureau Central de la CIE, Paris, 1974. The CIE standard chromaticity diagram includes the color points of black body radiators at various temperatures. The locus of blackbody chromaticities on the x,y-diagram is known as the Planckian locus. Any emitting source represented by a point on this locus may be specified by a color temperature. A point near but not on this Planckian locus has a correla~ed color temperature (CCT) because lines can be drawn from such points to intersect the Planckian locus at this color temperature such that all points look to the average human eye as having nearly the same color. Luminous efficacy of a source of light is the quotient of the total luminous flux emitted by the total lamp power input as expres~ed in lumens per watt (LPW or lm/~).

It is an object of the present invention to provid~ a bulb which increase~ the color render~ng index for an electrodeless high intensity discharge lamp utilizing the , .

D 92-1-103 ~ 4 ~ ~ PATENT

NaIScI3LiI chemi~try while maintaining the efflcacy and long life charac~eristic of such lamps.

It is another object of ~he pre~ent invention to improve the color renderinq properties of the emi~ted light while maintaining a long bulb life.

It is anoth~r object of the present invention to increase the density of the rare earth species above the density obtainable with a rare earth iodide alone.

It is another object of the present invention to increase the density of the rare earth atoms in the gas discharge by forming a complex molecule containing the rare earth element.

It is another object of t~e present invention to have a low wall temperature of the qas discharge envelope which is conducive to a lonq lamp life.
Other objects and advantages of the present invention are apparent from reading the specification and claims.

The present invention provid~s a bulb for an electrodeless discharge lamp for producing visible ligh~ :
having an enhanced color rendering index because of an improved emission spectrum during operation. Structurally, the bulb comprises a sealed transparent envelope with a continuous wall and containinq a chemical fill. During operation of the bulb by energization of the chemical fill -:
with a high frequency electromagnetic field, the bulb is operable at a desirable wall temperature conducive to long life while emitting the visible radiation.

The chemical fill comprises an inert starting qas, mercury, alkali metal iodides, scandium iodide, and at least '.: - . ~.~:: : ': . . ,, ~ f , ,.` , ' ~ . , ': :::: .. . - :

D 9~ 103 ~ PATENT

one iodide of a rare earth. The alkali metal iodides comprises sodium iodide and lithium lodide. The iodide of a rare earth and scandium ~odide are present in amount~
sufficient to form a complex for increasing the den~ity of the rare earth in the discharge gas during lamp operation to effect a color rendering index greater than about 80 and a color temperature betwsen about 3000 to about 5000 Kelvin.
Due to the increased density of the rare earth in the discharge gas at lower temperatures of operation, the wall temperature of the gas discharge tube is desirably maintalned at a temperature to enhanced the life of the bulb.

BRIEF DESCRIPTION OF T~E DRAWINGS
In the drawings:

FIG. 1 is a representation of a microwave lamp system showing a schematic representation of the hulb during operation.

FIG. 2 shows a process for preparing bulbs by a three part construction. FIG. 2A shows bulb components. FIG. 2B
and FIG. 2C show construction steps. FIG. 2D shows the completed tube.

A detalled description of thi~ invention is given below. This descriptlon uses the Figures cited here. Other and further advantages of this invention will become apparent to those skilled in the art through this description.

DETAILE:D DESCRIPTION OF THIE INVl:NTION

Referring to FIG. 1, a representation of a mlcrowave lamp is shown. A bulb 1 is a transparent envelope D 92-1-103 ~ PATENT

contalning a chemlcal fill 4 within an ex~erior wall 3. The fill forms a gas dlscharge 5 during lamp operatlon. The wall material is preferably a fused silica or ceramic alumina (PCA). Yttria or sapphire which is a single S crystalline alumina may be used. Since the bulb 1 i 5 utilized in an electrodless lamp, the continuous wall has an internal surface uninterrupted by an electrically conducting path extending through the wall 3 as is found in conventional electroded bulbs.
The purpose of the metal halide chemical fill 4 is to generate sufficient optical rare earth emissions without chemical interaction with wall 3. The arc tube can have various shapes, however, a cylindrical arc tube with hemi-spherical end chambers is most practical. A football shapeis more difficult to fabricate, but it will have a desirable increased end-temperature.

A chemical fill which forms an electrical dischar~e sustaining gas for emittinq radlation is disposed within the transparent envelope. The chemical fill contains a base chemistry of an inert starting gas, mercury, alkali metal iodides, and scandium iodide. The desired base chemistry contribu~es to the desirable lamp characteristics of low wall temperature, high LPW, moderats CRI, and long life.
The lamp emission due to the base chemistry is approximately on the black body chromaticity locus.

In addition to the appropriate base chemistry, the chemical fill comprises at least one iodide of a raxe earth element which is at least partially vaporized during lamp operation. The iodide of a rare earth and scandium lodide are present in a molar ratio sufficient to form a complex for increasing the concentration of the rare earth in the discharge gases during lamp operation at a low arc tube wall temperature. Due to the formation of the complex, the vapor - :- . . . ~ . .-- : .
. . -: -: "

- .: , .
~ .

~ D 92-1-103 PATENT

2 ~
phase concentration of the rare earth is lncreased at the arc tube wall temperature beyond what i~ obtainable using the rare earth iodide alone. The wall temperature of the arc tube in the lamp of the present invention is preferably maintained between about 690 and about 960 degree~ Celqius, more preferably between about 690 and about 730 degrees Celsius.

In accordance with the principles of the present invention, the improved chemical fill comprising the base chemistry and at least one rare earth iodide enhances the color rendering index of the lamp. Due to the presence of the rare earth atoms in the discharge ga~, the lamp has a color rendering index greater than about 80. Preferably, the color rendering index is greater than 85 and more preferably greater than 90.

High color rendering indices, on the order of about 90, are easier to realize at high correlated color temperatures (CCT). In a preferred embodiment, the present invention achieves high Ra at relatively low CCT between 3000 and 4000 Kelvin.

During lamp operation, the amount of rare earth in the g~s discharge is sufficient to produce an enhanced color rendering index while maintaining the relatively low arc tube wall temperature that is conducive to long lamp life.
The formation of complex molecules of the rare earth with scandium iodide results in an increased density of rare earth atoms in the gas di~charge.

In the present invention, rare earth is present in an amount sufficient to complex with scandium iodide in order to increase the density of the rare earth atoms in the vapor during lamp operation to the desired level. Preferably the molar ratio of the rare earth iodide to scandium io~ide in D 92-l-103 ~ PATENT

the fill is between about 1:1 to about 30:1, and more preferably between about 5:1 to about 20:1.

Due to their many emission llnes, all rare earths may enhance the arc performance of a lamp, at least to some degree and ln some respect. The rare earths are selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, ~b, Dy, Ho, Er, Tm, Yb, Lu and mixtures thereof. The choice of rare earth depends on the desired radiation characteristics.
The preferred rare earths for enhanced CRI are the lodides of cerium ~Ce), praseodymium (Pr), neodymium (Nd), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), and lutetium (Lu). According to one embodiment the rare earth iodide is present as a single rare earth iodide selected from the above preferred group. Even more preferred are the rare earth iodides of cerium~
praseodymium, dysprosium, holmium, and thulium.

A charge of mercury is present in a sufficient amount so as to ~stablish the electrical characteristics of the lamp by desirably increaslng the electric field strength to sustain a desirable power loading. Such an amount should provide an operating mercury pressure between 1 to about 100 atmospheres, and preferably between about 1 to about 20 atmospheres.

In addition to mercury, a small charge of an inert ionizable starting gas such as argon is contained within the transparent envelope. It is contemplated that other noble gases can be substituted for argon provided an appropriate pressure i8 maintained that is conducive to starting the lamp.

To achieve the above discu~sed desirable lamp properties, the scandium iodide and the alkali metal iodides are present in the fill and in the discharge gas during lamp D 92-1-103 ~ PATENT

operation. These ingredients form a base chemistry which i~
conducive to the low wall temperature and long lamp life.
These ingredients also improve color quality by adding a variety of lines to the emission spectrum and are preferably present ln amounts for producing emission wlth its color substantially on the black body radiator chromaticity locus.
The molar ratio of sodium iodide to scandium iodide is between about 5:1 to about 25:1. The ratio of sodium iodide to lithium iodide is between about 1:1 to about 5:1.
The alkali metal iodides adjust the current-voltage characteristics, improve the color quality, and contribute to lumen output of the lamp through strong emissions. The scandium iodides signifivantly improves the "efficacy" in lumens per watt (LPW) and the CRI. The addition of rare earth iodides further improves the LPW to greater than 90 and preferably greater than 100, and, also, improve~ the CRI
to greater than U0 while maintaining CCT between 3000 and 5000 Kelvin.
In the present invention, the selection of fill ingredients results in a desirable color temperature between 3000 K and 5000 K, more preferably between about 3000 to about 4000 Kalvin. The molar ratios of the ingredients are selected also so that the resulting emission color is near the highly desirable black body (BB) chromaticity locus at this desired color temperature.

In addition to the above-mentio~ed fill ingredients, scandium, thorium, cadmium, or zinc may be added to the fill as metals or alloys to ad~ust the metal/iodine ratio in the lamp and to getter oxygen impurities. The preferred additive is scandium. For a low wattage metal iodide discharge lamp with a lamp wattage less than 175 wat~s, e.g., between 40 to 1~0 watts, the scandium metal weight dosage is preferably about 100 micrograms per cubic .

D 92-1-103 ~ PA~EN~

centimeter of arc tube volume at all wattages. The total fill weight varies with lamp operating power between about 4 and about 20mg. For example, the 100 watt lamp fill is preferably between about 4mg and about 8 mg, and more preferably between about 5.5 and about 6.5 mg.

As illustrated schematicly in FIG. 1, the microwave power sourc~ 7 may be solid state, magnetron or some other tube coupled over a transmission line 9 in the form of a waveguide, coaxial line or microstrip line. The impedance matching network 11 and EM-field coupler 13 delivers power to the bulb 1. A - A is the impedance reference plane. The light emitting plasma discharge 5, the lamp fill 4, the bulb 1 and the field coupler 13 comprise the effective impedance matched load (field coupled lamp load~ that the power supplying microwave transmission line sees.

The lamp is powered by high frequency ~microwave) excitation of the discharge that is the ma~ched load of a microwave circuit (for maximum power transfer) operating in the frequency ranqe from 100 MHz to 300 GHz. The lamp ls impedance matched to the impedance of the transmission line 9 from the driving source for such load circuit conditions the lamp represents when it is operating in equllibrium at lamp design input power~ The range of design input power for the microwave lamps is typically from 10 Watt to 1 kWatt.

When the lamp is fully warmed up and operating in equilibrium at the design power, the arc tube wall temp~rature at the center is preferably in the range of 690 to 730 degrees Cels~us. This, of course, depends on the lamp design parameters such as mercury pressure, arc tub~
wall thickness and wall-loading (W~cm2) of the arc tube.

.,,, . . . . , ~ . ~ , . .. . . . . . .. . .. .. . . . . . .

D 92-1-103 ~ PATENT

DETAILED EXAMPLE

Bulb 1 is a high purity fused silica with zero hydroxyl ion content, such as GTE-Sylvania water free fused silica or General Electric GE 214A hydroxyl free fused silica. The bulb 1 is formed from tubing having a size tI.D. and O.D.) which is determined according to the desired and allowable wall loadinq for the particular discharge lamp.
As shown in FIG. 2A, the quartz tube 43 is first attached to a quartz rod or support member 45. As shown in FIG. 2B, a funnel 47 is inserted into the resultlnq assembly. The charge of chemical fill is introduced through the funnel 47. FIG. 2C shows the quartz tube 43 necked down at a contriction 49 for evacuaation and sealing. FIG. 4D
shows the completed bulb 1 which includes support 45 which may be used to hold and positioned the bulb 1 in the EM-field coupling structure.
Because the chemical fill is highly hygroscop~c, the bulb blanks as shown in Fig. 2B are prepared for filling by baking ~hem in a furnace at temperatures of 1000-C and ultra high vacuum by attaching them to a vacuum system. This is ~5 done by means of a NUPROR B series valve (SS 8BG TSW) that i~ equipped with a quick-connect (CAJON, Ultra-Torr) for attaching the fill tube of bulb blank to the valve. The baked bulb still under vacuum is put in~o an argon filled drybox and op~ned to the argon. The bulb is then is filled with the liq~id and solid components of the fill, the valve is again closed, and then the bulb is transferred transferred from the drybox and attached to the gas fill system. After the argon is pumped out, the bulb is filled to the desired pressure with a noble gas such as argon, xenon or a Penning mixture and then tipped off. Th~ back-filled gas serves as the starting gas in the lamp. The : :: - : : - ::: : . - :
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~` ` :' : : - ' , .

D 92-1-103 ~ PATENT

following fill is for a bulb with a volume of 1.25 cm3 and the total fill weight is 19 mg. Typical fill weight~ are from about 4 to about 50 mg~cm3.
_ _ _ _ s Hg 67.~0 ~mol Li 4.03 ~mol ~as iodide) Na 10.20 ~mol (as iodide) Sc 0.42 ymol (as iodide) Tm 6.82 ~mol (as iodide) I 35.95 ymol (as metal iodide) Sc ~.~9 ~mol (as metal) Ar0.5 to 50 torr (as gas) While there has been shown and described what at present is considered the preferred embodiment of this invention, it will be apparent to those skilled in the art that various changes and modification~ may be made therein without departing from the invention as defined by the appended claims.

Claims

1. A bulb for an electrodeless lamp having an enhanced color rendering index and emission spectrum when energized during operation comprising:
a transparent envelope having a continuous wall and containing a chemical fill for producing a gas discharge for emitting visible radiation and producing an operating temperature of said wall when energized;
said chemical fill comprising an inert starting gas, mercury, alkali metal iodides consisting essentially of sodium iodide and lithium iodide, scandium iodide, and at least one iodide of a rare earth; and said iodide of a rare earth and said scandium iodide being present in a molar ratio for increasing the concentration of said rare earth in the discharge so that lamp emission has its color temperature between 3000 Kelvin and 5000 Kelvin and its color rendering index greater than about 80 at a suitable wall temperature.

2. A bulb for an electrodeless lamp in accordance with Claim 1 wherein the molar ratio of said iodide of a rare earth to scandium iodide is between about 1:1 to about 30:1.

3. A bulb for an electrodeless lamp in accordance with Claim 2 wherein the molar ratio of said sodium iodide to said scandium iodide is between about 5:1 to about 25:1.

4. A bulb for an electrodeless lamp in accordance with Claim 2 wherein the molar ratio of said sodium iodide to said lithium iodide is between about 1:1 to about 5:1.

5. A bulb for an electrodeless lamp in accordance with Claim 2 wherein said iodide of a rare earth is selected from the group consisting of the iodides of cerium, praseodymium, neodymium, dysprosium, holmium, erbium, thulium, lutetium and mixtures thereof.

6. A bulb for an electrodeless lamp in accordance with Claim 5 wherein said iodide of a rare earth is selected from the group consisting of the iodides of cerium, praseodymium, dysprosium, holmium, thulium or mixtures thereof.

7. A bulb for an electrodeless lamp in accordance with Claim 2 wherein said iodide of a rare earth is a single rare earth iodide selected from the group consisting of the iodides of cerium, praseodymium, neodymium, dysprosium, holmium, erbium, thulium, and lutetium.

8. A bulb for an electrodeless lamp in accordance with Claim 7 wherein said iodide of a rare earth is an iodide of cerium, praseodymium, dysprosium, holmium, or thulium.

9. A bulb for an electrodeless lamp in accordance with Claim 1 wherein said scandium iodide and said alkali metal iodides are present in amounts for producing emission with its color substantially on the black body radiator chromaticity locus.

10. A bulb for an electrodeless lamp in accordance with Claim 9 wherein said iodide of a rare earth iodide is selected from the group consisting of the iodides of cerium, praseodymium, neodymium, dysprosium, holmium, erbium, thulium, lutetium and mixtures thereof.

11. A bulb for an electrodeless lamp in accordance with Claim 10 wherein the molar ratio of said sodium iodide to said scandium iodide is between about 5:1 to about 25:1.

12. A bulb for an electrodeless lamp in accordance with Claim 11 wherein the molar ratio of said sodium iodide to said lithium iodide is between about 1:1 to about 5:1.

13. A bulb for an electrodeless lamp in accordance with Claim 12 wherein said iodide of a rare earth is selected from the group consisting of the iodides of cerium, praseodymium, dysprosium, holmium, or thulium.

14 A bulb for an electrodeless lamp in accordance with Claim 1 wherein said wall temperature is from about 690 to about 960 degrees Celsius and said envelope has a wall loading in the range of about 12 to 17 watts/cm2.

A bulb for an electrodeless lamp in accordance with Claim 14 wherein said wall temperature is from about 690 to about 730 degrees Celsius.

16. A bulb for an electrodeless lamp in accordance with Claim 1 wherein said envelope has a total amount of fill between about 4 to about 50 mg/cm3.

17. Each and every novel feature or novel combination of features herein disclosed.