Rare earth halide light source with enhanced red emission

This invention teaches a novel high pressure electric discharge lamp which has the desired properties of high efficacy, good color rendering, and a warm color temperature. These desired properties are attained by utilizing as fills the rare earth iodides in conjunction with calcium halides and, or sodium halides. Efficient visible emission from the rare earth atomic and molecular fragments in the discharge is combined with the red emission from calcium monohalide to provide an efficient, warm source.

FIELD OF THE INVENTION 
This invention relates to a high pressure electric discharge lamp. More 
particularly, this invention relates to a high pressure electric discharge 
lamp having an enhanced red emission. 
BACKGROUND OF THE INVENTION 
High pressure electric discharge lamps containing Hg and rare earth iodides 
are commercially available and used for studio lighting. These sources 
have high efficacy, greater than 80 LPW, good color rendering, CRI approx. 
equal to 85, and a high color temperature, approx. 6000.degree. K. The 
high color temperature is compatible with photographic film. Sources for 
more general illumination should have the high efficacy and good color 
rendering of the rare earth studio lamps, but a warm color temperature, 
approximately 3,000.degree. K., more representative of an incandescent 
source, would be desirable. 
The high efficacy and good color rendering of rare earth halide lamps 
arises from both atomic and molecular emission from the arc. Many rare 
earth atomic emission lines in the visible region of the spectrum 
originate from the central core of the arc. Superimposed on the atomic 
emission spectrum is molecular emission from the rare earth subhalides, 
which comes from the mantle of the arc. Since the radiation from the rare 
earth halide sources is deficient in the red, compared to the blue and 
green, a high color temperature results. 
One approach to lowering the color temperature is the addition of alkali 
atoms, such as sodium or lithium. These are added as the iodides to reduce 
reaction with the lamp envelope. The discharge typically contains cesium 
iodide to help broaden and stabilize the arc, and provide a source of 
atoms with low ionization potential (cesium ionization potential=3.9 eV). 
Ionized cesium provides the electrons necessary for maintaining the 
discharge and reduces the cesium neutral emission in the IR which lowers 
the efficacy of the lamp. Ionization of cesium also lowers the extent of 
ionization of the rare earth atoms. This is desirable because maximization 
of rare earth neutral atoms increases the visible emissions. Addition of 
sodium alone lowers the color temperature and increases the efficacy, but 
at the expense of color rendering. The sodium emission is predominantly 
located at 590 nm and tends to dominate the spectrum. Also, addition of 
the sodium can increase the rare earth ion to neutral ratio because of the 
higher ionization potential of sodium relative to cesium. Addition of 
lithium results in emission at 671 nm. Although emission from this line 
lowers the color temperature, the emission is far outside the photopic 
response, and efficacy decreases. 
SUMMARY OF THE INVENTION 
In accordance with one aspect of the present invention, a new and imroved 
electroded high pressure electric discharge lamp having an enhanced red 
emission comprises an outer envelope, a base, a refractory inner envelope, 
an inner refractory envelope support frame, two electrodes, a fill gas and 
electrical connectors. The fill gas consists essentially of mercury, 
calcium halides, an alkali halide, rare earth halides and an inert gas. 
The calcium halide, the alkali halide and rare earth halides are exclusive 
of fluorides. The fill gas is contained within the refractory inner 
envelope. The refractory inner envelope, the support frame, and the 
electrical connectors are contained within the outer envelope. The base is 
connected to the outer envelope and the electrical connectors. The 
electrical connectors are connected to the base, the refractory inner 
envelope and the electrodes. 
In accordance with another aspect of the present invention, a new and 
improved electroded high pressure electric discharge lamp having an 
enhanced red emission comprises an outer envelope, a base, a refractory 
inner envelope, an inner envelope support frame, two electrodes, a fill 
gas and electrical connectors. The fill gas consists essentially of 
mercury, a calcium halide, a sodium halide, rare earth halides and an 
inert gas. The calcium halide, the sodium halide, and the rare earth 
halides are exclusive of fluorides. The fill gas is contained within the 
refractory inner envelope. The inner envelope, the support frame, the 
electrical connectors are contained within the outer envelope. The base is 
connected to the outer envelope and the electrical connectors. The 
electrical connectors are connected to the base, the inner transparent 
envelope and the electrodes. 
In accordance with still another aspect of the present invention, a new and 
improved electrodeless high pressure electric discharge lamp having an 
enhanced red emission comprises a refractory inner envelope containing a 
fill gas. The fill gas consists essentially of mercury, a calcium halide, 
an alkali halide, rare earth halides and an inert gas. The calcium halide, 
the alkali halide and the rare earth halides are exclusive of fluorides. 
The fill gas is contained within the refractory inner envelope. 
In accordance with still another aspect of the present invention, a new and 
improved electrodeless high pressure electric discharge lamp having an 
enhanced red emission comprises a refractory inner envelope containing a 
fill gas. The fill gas consists essentially of mercury, a calcium halide, 
a sodium halide, rare earth halides and an inert gas. The calcium halide, 
the sodium halide, and the rare earth halides are exclusive of fluorides. 
The fill gas is contained within the refractory inner envelope.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawing with greater particularity, there is shown in 
FIG. 1 one embodiment of the present invention, an electroded high 
pressure electric discharge lamp 1, which comprises an outer vitreous 
envelope 2 of generally tubular form having a central bulbous portion 3. 
Envelope 2 is provided at its end with a re-entrant stem 4 having a press 
through which extend relatively stiff lead-in wires 5 and 6 connected at 
their outer ends to the electrical contacts of the usual screw type base 7 
and at their inner ends to the arc tube 8 and harness 9. 
Arc tube 8 is generally made of quartz although other types of material may 
be used such as alumina, yttria or Vycor.TM., the later being a glass of 
substantially pure silica. Sealed in the arc tube 8 at the opposite ends 
thereof are main discharge electrodes 10 and 11 which are supported on 
lead-in wires 12 and 13 respectively. Each main electrode 10 and 11 
comprises a core portion which is made by a prolongation of the lead-in 
wires 12 and 13 and may be prepared of a suitable metal such as, for 
example, molybdenum and tungsten. The prolongations of these lead-in wires 
12 and 13 are surrounded by molybdenum or tungsten wire helixes. 
An auxiliary starting probe or electrode 14, generally made of tantalum or 
tungsten is provided at the base and of the arc tube 8 adjacent the main 
electrode 11 and comprises an inwardly projecting end of another lead-in 
wire 15. 
Each of the current lead-in wires described have their ends welded to an 
intermediate foil section made of molybdenum which are hermetically sealed 
within the pinched sealed portions of arc tube 8. The foil sections are 
very thin, for example, approximately 0.0008" thick and go into tension 
without rupturing or scaling off when the heated arc tube pulls. 
Relatively short molybdenum wires 15, 16, and 17 are welded to the outer 
ends of the foil sections foil and serve to convey current to the various 
electrodes 10, 11, and 14 inside the arc tube 8. 
Insulators 18 and 19 cover lead-in wires 15 and 16 respectively to preclude 
an electrical short between the lead-in wires 15 and 16. Molybdenum foil 
strips 20 and 21 are welded to lead-in wires 15 and 16. Foil strip 21 is 
welded to resistor 22 which in turn is welded to the arc tube harness 9. 
Resistor 22 may have a value, for example, 40,000 ohms and serves to limit 
current to auxiliary electrode 14 during normal starting of the lamp. 
Molybdenum foil strip 20 is welded directly to stiff lead-in wire 5. 
Lead-in wire 17 is welded at one end to a piece of foil strip which is 
sealed in the arc tube 8. The other end of the foil strip is welded to 
lead-in wire 12 which is welded to electrode 10. Molybdenum foil strip 23 
is welded to one end of lead-in wire 17 and at the other end to the 
harness portion 24. The pinched or flattened end portions of the arc tube 
8 form a seal which can be of any desired width and can be made by 
flattening or compressing the ends of the arc tube 8 while they are 
heated. 
The U-shaped internal wire supporting assembly or arc tube harness 9 serves 
to maintain the position of the arc tube 8 sequentially coaxial with the 
envelope 2. To support the arc tube 8 within the envelope 2 lead-in wire 6 
is welded to base 25 of harness 9. Because stiff lead-in wires 5 and 6 are 
connected to opposite sides of the power line, they must be insulated from 
each other, together with all members associated with each of them. Clamps 
26 and 27 hold arc tube 8 at the end portions and fixedly attached to legs 
28 of harness 9. Harness portion 24 bridges the free ends of harness 9 and 
is fixedly attached thereto by welding for imparting stability to the 
structure. The free ends of the harness 9 are also provided with a pair of 
metal leaf springs 29 frictionally engaging the upper tubular portion of 
lamp envelope 2. A heat shield 30 is disposed beneath the arc tube 8 and 
above resistor 22 so as to protect the resistor from excessive heat 
generated during lamp operation. 
The arc tube 8 is provided with a fill gas consisting essentially of 
mercury, rare earth halides, a calcium halide, an alkali halide, and an 
inert gas. The rare earths are selected from the group consisting of La, 
Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and mixture thereof. 
The halides, exclusive of fluorides are selected from the group consisting 
of chlorine, bromine, iodine, and mixtures thereof. The inert gas can be 
selected from the group consisting of neon, argon, krypton, xenon, and 
mixtures thereof. The alkali halide can be selected from the group 
consisting of the halides of lithium, sodium, potassium, rubidium, cesium, 
and mixtures thereof. The calcium halide can be selected from the group 
consisting of calcium chloride, calcium bromide, calcium iodide, and 
mixtures thereof. The fill gas of the present invention has been used in 
electrodeless lamps as well as the electroded lamps. 
One particular fill of the present invention consists essentially of 
mercury, argon, and the halides of cerium, thulium, cesium, sodium, and 
calcium. Another fill of the present invention consists essentially of 
mercury, argon, and the halides of cerium, thulium, sodium and calcium. 
Still another fill of the present invention consists essentially of 
mercury, argon, and the halides of cerium, thulium, cesium, and calcium. 
In FIG. 2, an emission spectrum is shown of a electrodeless high pressure 
electric discharge lamp containing a lamp fill of mercury, cerium iodide, 
thulium iodide, cesium iodide and argon. The emission spectrum shown in 
FIG. 2 has poor red color rendition. However, in FIG. 3, in accordance 
with the present invention, an emission spectrum is shown of a 
electrodeless high pressure electric discharge lamp containing a lamp fill 
of calcium iodide in addition to mercury, cerium iodide, thulium iodide, 
cesium iodide and argon which has good red color rendition. The emission 
spectrum shown in FIG. 3 has an increased emission in the 620 nm and 650 
nm region resulting in a warmer color temperature and an increased red 
color rendition as compared to the emission spectrum shown in FIG. 2. 
Electroded lamp spectra are similar. 
In FIG. 4, in accordance with the present invention, an emission spectrum 
of an electrodeless high pressure electric discharge lamp containing a 
lamp fill of calcium iodide and sodium iodide in addition to mercury, 
cerium iodide, thulium iodide and argon is shown. This lamp also shows an 
increased emission in the 620 nm to 650 nm region resulting in a warmer 
color temperature and an increased red color rendition. Electroded lamp 
spectra are similar. 
FIG. 5 is a schematic representation of an embodiment of a high-pressure 
electrodeless discharge apparatus in accordance with the present 
invention. Shown in FIG. 5 is a high-pressure electrodeless discharge lamp 
32 having a discharge chamber 33 made of a light transmitting substance, 
such as quartz. Chamber 33 contains a volatile fill material 34. Volatile 
fill material 34 of discharge chamber 33 includes mercury, cerium iodide, 
thulium iodide, cesium iodide, calcium iodide and argon or includes 
mercury, cerium iodide, thulium iodide, sodium iodide, calcium iodide and 
argon. An RF coupling arrangement includes a spiral coil electrode 35 
disposed around discharge chamber 33 and attached to fixture 36. A 
grounded conductive mesh 37 surrounds the discharge chamber 33 and spiral 
coil electrode 35 providing an outer electrode which is transparent to 
radiation from the discharge chamber 33. Spiral coil electrode 35 and 
grounded conductive mesh 37 are coupled by a suitable coaxial arrangement 
38, 39 to a high frequency power source 40. The radio frequency electric 
field is predominantly axially directed coincident with the spiral axis of 
spiral coil electrode 35 and causes an arc to form within discharge 
chamber 33. 
As used herein, the phrase "high frequency" is intended to include 
frequencies in the range generally from 100 MHz to 300 GHz. Preferably, 
the frequency is in the ISM band (i.e., industrial, scientific and medical 
band) which ranges from 902 MHz to 928 MHz. A particularly preferred 
frequency id 915 MH. One of the many commercially available power sources 
which may be used is an AIL Tech Power Signal Source, type 125. 
Visible radiation is produced by the resulting arc discharge within the 
lamp as depicted by the emission spectrum depicted in FIGS. 2, 3 and 4. 
Specific details of the structure of the apparatus of this general type 
are shown in U.S. Pat. No. 4,178,534 which issued Dec. 11, 1979, to 
McNeill, Lech, Haugsjaa, and Regan entitled "Method Of And Apparatus For 
Electrodeless Discharge Excitation". 
The emission spectrum produced by the addition of calcium iodide is 
efficiently produced in a rare earth halide discharge and originates from 
the mantle of the discharge like the rare earth subhalide emission. There 
are relatively few atomic calcium emission lines in the visible, 423 nm 
being the strongest, and thus, atomic calcium emission does not 
significantly alter the emission spectrum of that discharge. In addition, 
the ionization potential of calcium at 6.1 eV is sufficiently high that 
little ionization of calcium occurs. 
The vapor pressures of all the rare earth iodides are very close at 
1100.degree. K. and the temperature dependences of their vapor pressures 
are also similar. Thus, it is possible to utilize several rare earth 
iodides in a lamp and derive additive properties from their emission. 
Lamps containing rare earth halide additives must be operated at higher 
wall loadings and subsequent higher wall temperatures than lamps 
containing more volatile metal halides. The vapor pressure of calcium 
iodide is similar to that of the rare earth iodides. Consequently, 
addition of calcium iodide to the lamp does not require a change in the 
wall loading of rare earth containing lamps. The high wall temperature can 
increase wall reactions and decrease the lifetime of the lamp. However, 
both electrodeless and electroded lamps made from quartz and containing 
fills as described above were run successfully for hundreds of hours. One 
electroded lamp was tested for over 800 hours. These lamps also started 
easily and repeatedly. Alternate envelope materials such as alumina or 
yttria, which are designed for higher temperature operation than quartz, 
could be utilized to increase the operating lifetime of the source. The 
chemistry described herein should be applicable to ceramic envelopes. 
TABLE I 
______________________________________ 
RARE EARTH METAL HALIDE SUMMARY 
LAMP FILL RANGES [mg/cm.sup.3 ] 
(Buffer gas pressure in torr) 
Ar 
Fill Ar Elec- 
Type Hg CeI.sub.3 
TmI.sub.3 
CaI.sub.2 
CsI NaI RF troded 
______________________________________ 
High 11.0 4.0 4.0 13.6 4.8 -- 10.0 60 
Preferred 
9.0 2.5 2.5 8.5 3.0 -- 7.5 50 
Most 7.0 1.0 1.0 3.4 1.2 -- 5.0 45 
Preferred 
Preferred 
4.0 0.5 0.5 1.8 0.6 -- 2.8 15 
Low 1.0 0.1 0.1 0.3 0.1 -- 0.5 10 
C 
High 11.0 4.0 4.0 13.6 -- 11.2 10.0 60 
Preferred 
9.0 2.5 2.5 8.5 -- 7.0 7.5 50 
Most 7.0 1.0 1.0 3.4 -- 2.8 5.0 45 
Preferred 
Preferred 
4.0 0.5 0.5 1.8 -- 1.4 2.8 15 
Low 1.0 0.1 0.1 0.3 -- 0.1 0.5 10 
______________________________________ 
TABLE II 
__________________________________________________________________________ 
RARE EARTH METAL HALIDE LAMP SUMMARY 
RF QUARTZ LAMPS 
Wall 
Efficacy 
Color Wall Loading 
Lamp 
.eta. 
Tcc CRI 
Temp 
Fill 
Calcium 
Alkali 
Alkali 
.theta. 
No. [lm/W] 
[K] Ra [.degree.C.] 
Type 
RE RE Additive 
[W/cm.sup.2 ] 
__________________________________________________________________________ 
86-016 
70.00 
4564 
82.6 
&gt;1100 
B 3.06 3.05 
0.75 40.3 
86-014 
79.4 4886 
79.4 
&gt;1100 
B 1.53 1.90 
0.75 40.1 
86-013 
86.0 5210 
74.0 
1095 
B 0.77 1.33 
0.75 39.7 
86-003 
97.7 4888 
76.5 
&gt;1100 
B 1.53 1.01 
0.40 39.3 
85-139 
90.2 4706 
90.9 
&gt;1100 
B 3.06 1.02 
0.25 39.7 
85-140 
89.2 4587 
80.7 
&gt;1100 
B 0.77 1.03 
0.58 37.7 
86-006 
50.9 4815 
81.8 
&gt;1100 
B 3.06 4.06 
1.00 40.7 
86-005 
66.2 4620 
82.8 
&gt;1100 
B 1.53 2.53 
1.00 39.5 
86-004 
79.0 4957 
76.6 
&gt;1100 
B 0.77 1.77 
1.00 40.7 
__________________________________________________________________________ 
These data show fill optimization studies resulting in L86018 to 020. (Se 
Table VI) The ratios shown are molar ratios. RE refers to the total molar 
rare earth concentration. Additive includes all metals except alkali and 
mercury. 
TABLE III 
__________________________________________________________________________ 
RARE EARTH METAL HALIDE LAMP SUMMARY 
RF QUARTZ LAMPS 
Wall 
Efficacy 
Color Wall Loading 
Lamp 
.eta. 
Tcc CRI 
Temp 
Fill 
Calcium 
Alkali 
Alkali 
.theta. 
No. [lm/W] 
[K] Ra [.degree.C.] 
Type 
RE RE Additive 
[W/cm.sup.2 ] 
__________________________________________________________________________ 
86-054 
76.8 2917 
84.97 
&gt;1100 
C[Na] 
3.06 8.2 2.0 40.7 
86-053 
77.3 3776 
85.38 
&gt;1100 
C 3.06 3.69 
0.90 40.9 
86-044 
87.6 3528 
81.85 
1100 
C 3.06 4.92 
1.20 40.6 
86-043 
88.3 4043 
84.75 
&gt;1100 
C 3.06 2.46 
0.60 40.5 
86-042 
91.6 4072 
85.79 
&gt;1100 
C 3.06 1.23 
0.30 41.4 
__________________________________________________________________________ 
Above data show lamp performance as a function of sodium concentration. 
TABLE IV 
__________________________________________________________________________ 
RARE EARTH METAL HALIDE LAMP SUMMARY 
RF QUARTZ LAMPS 
Wall 
Efficacy 
Color Wall Loading 
Lamp 
.eta. 
Tcc CRI Temp 
Fill 
Calcium 
Alkali 
Alkali 
.theta. 
No. [lm/W] 
[K] Ra [.degree.C.] 
Type 
RE RE Additive 
[W/cm.sup.2 ] 
__________________________________________________________________________ 
86-056 
78.5 4942 
77.91 
1000 
B 2.45 0.98 
0.284 
41.0 
86-050 
85.3 4712 
&gt;78.61 
1100 
B 2.04 0.82 
0.270 
40.7 
86-049 
71.7 4805 
81.97 
1100 
B 2.45 0.98 
0.284 
40.5 
86-048 
80.4 4696 
&gt;82.56 
1100 
B 3.06 1.23 
0.30 40.5 
__________________________________________________________________________ 
Above data show lamp performance as a function of rare earth 
concentration. 
TABLE V 
__________________________________________________________________________ 
RARE EARTH METAL HALIDE LAMP SUMMARY 
RF QUARTZ LAMPS 
Wall 
Efficacy 
Color Wall Loading 
Lamp 
.eta. 
Tcc CRI 
Temp 
Fill 
Mercury Concentration 
.theta. 
No. [lm/W] 
[K] Ra [.degree.C.] 
Type 
[micromole] [W/cm.sup.2 ] 
__________________________________________________________________________ 
86-026 
69.5 4690 
76.6 
1100 
B 123.4 41.2 
86-025 
74.4 4576 
79.6 
1100 
B 102.7 40.9 
86-024 
67.8 4280 
94.0 
1100 
B 41.1 41.2 
86-023 
80.4 4642 
82.0 
1100 
B 61.8 40.9 
__________________________________________________________________________ 
Above data show lamp performance as a function of Hg concentration for 
calcium/rare earth ratio of 3.06; alkali/rare ratio of 1.23; and, 
alkali/additive ratio of 0.30 all held constant. 
TABLE VI 
__________________________________________________________________________ 
RARE EARTH METAL HALIDE LAMP SUMMARY 
RF QUARTZ LAMPS 
Wall 
Efficacy 
Color Wall Loading 
Lamp 
.eta. 
Tcc CRI 
Temp 
Fill 
Calcium 
Alkali 
Alkali 
.theta. 
No. [lm/W] 
[K] Ra [.degree.C.] 
Type 
RE RE Additive 
[W/cm.sup.2 ] 
__________________________________________________________________________ 
86-020 
86.7 4661 
81.8 
&gt;1100 
B 3.06 1.23 
0.30 41.1 
86-019 
84.0 4495 
82.8 
&gt;1100 
B 3.06 1.23 
0.30 40.5 
86-018 
78.0 4492 
83.4 
&gt;1100 
B 3.06 1.23 
0.30 41.0 
__________________________________________________________________________ 
Above data show reproducibility of lamp performance for optimized type B 
fill. 
TABLE VII 
__________________________________________________________________________ 
RARE EARTH METAL HALIDE LAMP SUMMARY 
ELECTRODED QUARTZ LAMPS (60 Hz) 
Wall 
Efficacy 
Color Wall Loading 
Lamp 
.eta. 
Tcc CRI 
Temp 
Fill 
Calcium 
Alkali 
Alkali 
.theta. 
No. [lm/W] 
[K] Ra [.degree.C.] 
Type 
RE RE Additive 
[W/cm.sup.2 ] 
__________________________________________________________________________ 
86-065 
120 3679 
91.5 
-- C 3.06 4.92 
1.20 25.8 
86-034 
105 4613 
83.4 
-- B 3.06 4.92 
1.20 25.9 
__________________________________________________________________________ 
Note: 
The lower wall loading was due to evacuted outer envelope. 
Metal iodides are usually used as additives in high pressure discharge 
lamps because their vapor pressure is higher than the corresponding 
bromides or chlorides. When only atomic emission originates from the 
discharge there is no advantage to using a different halide. However, when 
molecular emission is present, an alternate halide or mixture of halides 
can shift the molecular emission and desirably alter the color properties 
of the lamp. This is the case for the rare earth and calcium halides. The 
emission from the monobromide and monochloride of calcium, like calcium 
iodide, is also in the wavelength region 600 nm to 640 nm. Thus, CaX, 
where X represents a halide atom, should be a good red emitter independent 
of which halides are present in the lamp. 
The addition of CaX.sub.2 and NaI is more effective in improving the 
desirous color properties of the rare earth lamp than the addition of NaI 
alone. Na tends to dominate the spectrum at 590 nm (yellow) and produces 
red light due to broadening of the resonance line. This typically causes a 
decrease in the color temperature and an increase in efficacy at the 
expense of color rendition. More red in visually acute region is added by 
the CaX emission. The addition of small amounts of NaI increases the 
efficacy, decreases the color temperature and even increases the color 
rendering index in the presence of CaI.sub.2 as shown in Table VII. 
EXAMPLES 
Table I entitled "Rare Earth Metal Halide Summary of Lamp Fill Ranges" list 
the lamp fills designated type B and type C. Fill type B contains Hg, 
CeI.sub.3, TmI.sub.3, CaI.sub.2, CsI and Ar and Fill type C contains Hg, 
CeI.sub.3, TmI.sub.3, CaI.sub.2, NaI and Ar. 
Table II entitled "Rare Earth Metal Halide Lamps Summary" in accordance 
with the present invention illustrate specific examples of lamps having 
the fill type B as designated in Table I. The efficacy, color temperature, 
color rendition index, wall temperature, fill type, the wall loading, and 
additive molar ratios are listed. 
Table III shows lamp data from individual lamps made with fill type C as 
designated in Table I. 
Table IV shows lamp data from individual lamps with fill type B. The lamp 
performance as a function of rare earth concentration is shown. Table V 
shows lamp data from individual lamps made with fill type B. The lamp 
performance as a function of mercury concentration is shown. 
Table VI shows reproducibility of lamp performance for the optimized type B 
fill. 
And Table VII shows lamp data for individual electroded quartz lamps at 60 
Hertz utilizing a type B and a type C fill. 
This new and improved invention provides for a novel high pressure electric 
discharge lamp which has the desired properties of high efficacy, good 
color rendition and a warm color temperature. Lamps of the present 
invention would be good sources for more general illumination especially 
those applications requiring high color rendering (e.g. department store 
illumination). 
While there has been shown and described what is at present considered the 
preferred embodiment of the invention, it will be obvious to those skilled 
in the art that various changes and modifications may be made therein 
without departing from the scope of the invention as defined by the 
appended claims.