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Патент USA US2112993

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April 5, 1938. '
Filed Nov. 27, 1935
Fig. 3. '
2 Sheets-Sheet 2
Fig. 4.
Patented Apr. 5, 1938
' 2,112,993
William Henry Le Maréchal and, John Norman
Aldington, Ashton-on-Ribble, England, assign
ors to Siemens Electric Lamps ‘and Supplies
Limited, London, England, a British company
Application November 2'7, 1935, Serial No. 51,758
In Great Britain December 8, 1934
This invention relates to electric lamps and
(Cl. 176-1)
Electric discharge lamps of the hot cathode
more particularly to an arrangement in which
more than one lamp comprises a lighting unit.
one of the lamps being an electric discharge lamp.
high pressure mercury vapour type are at pres
ent constructed with an inner. container in which
are the electrodes and mercury ?lling and an
As known electric discharge lamps of the hot
cathode high (vapour) pressure type have a
much higher e?iciency than the gas ?lled tung
outer container.
sten ?lament lamp assuming that a normal life
and supporting wires.
5 Claims.
The space between the inner
and outer containers is exhausted and. inciden
tally the space is partly occupied by connecting
According to a further
feature of the invention the auxiliary lamp .is
In common with other discharge lamps the situated in the outer container and the outer 10
hot cathode lamp requires, to maintain'stable container may be enlarged to accommodate the
working, to have in series a current limiting de- ' ?lament of the auxiliary lamp. The enlarge
is allowed in each case.
vice such as a choke in the case of an A. C. sup
ply or a resistance in the case of a D. C. supply.
It‘ may be noted also that the use of a choke has
an effect on the power factor and condensers
are generally associated with the choke to bring
about a correction of the power factor.
The cost of this additional apparatus is a dis
advantage and also militates against the use of
discharge lamps for ordinary households and in
‘places where wiring is already installed.
The present invention amongst other things
has in View an arrangement which obviates the
presence of ‘such additional apparatus which is
not in itself a source of illumination and. in fact
is energy consuming.
In the present invention we arrange‘ in series
with a ‘discharge lamp a lamp having a light emit
ting part which‘ has a positive resistance-tem
"perature cpe?icient such as a tungsten ?lament
However, regard must be paid to the fact that
The space between the outer and inner con
tainers may be ?lled with gases such as those
used in the tungsten ?lament gas ?lled lamps.
Also a thermal “cut on ” such as a bi-metallic
strip may be situated in the space and serve to
short circuit‘aj portion of the ?lament of the
auxiliary lamp.’
It may be noted that the tungsten ?lament
lamp contributes rays which compensate for the
lack of 'red rays in the spectrum of a mercury
?lled gas discharge lamp although the latter may ,
have additional metals in its ?lling to the same 30
further useful purpose as will be made clear byv
the following.
light emitted by the discharge lamp in starting
In the hot cathode high pressure mercury
up and must withstand practically the whole of
the mains voltage at the start and when the dis
vapour lamps the quantity of mercury contained
in the lamp is so adjusted that when the ‘lamp is
in full working and at its designed wattage the
mercury has been totally evaporated since ‘the
steepness of the volt-ampere curve in the case 110
charge lamp is in full working will have only a
part of the mains voltage across it.’
The additional metals can serve, however a
such a" lamp will govern the rate of increase of
ment may be at one end of the container which
may be more convenient for mounting the aux
iliary ?lament. On the other hand to get a bet 15
ter mixture of light the ?lament can be dis
tributed adjacent to the surface of the inner con
- .
We arrange that the. auxiliary lamp is of such
a wattage that on starting it allows the discharge
lamp to run up under the most favourable con
ditions and at a suitable time during the run
ning up, part of the ?lament of the auxiliary
‘where there‘is an-excess of mercury is a cause of
unstable working. When evaporation is com
plete the current ?owing’ may be increased with
out the voltage drop in the lamp increasing. This
lamp is put outpf action by being short circuited. state of a?airs is however disadvantageous to 45
Clearly also it would be possible to use morethan the life of a tungsten ?lament lamp which is in
one auxiliary lamp and cut one or more of them series since for a given percentage increase of
out of circuit.
mains voltage, the percentage increase of volts
The cutting out of part of the ?lament of the drop'in the ?lament lamp is much greater. The
50 auxiliary lamp may be done by an electromag
volt-ampere curve of a similar lamp which has
netic cut-out which is controlled by the voltage * however additional metals such as cadmium
across the discharge lamp terminals but we pre
and/or zinc in the ?lling is much less steep up
fer to use a thermal cut-out such as one of the
to thepoint where complete evaporation of the.
lei-metallic type which is subjected to heat emit
?lling takes place. _
ted by the discharge. lamp,
According to another feature of the invention 55
it is arranged that in a series arrangement of a
pears across the incandescent ?lament as is shown
hot cathode high pressure electric discharge lamp
by the steeply rising curve D. This shows that
the ?lling of which includes mercury and a lamp
having a positive-resistance temperature coe?i
cient su?icient additional metals are included in
the ?lling of_ the discharge lamp to ensure that
with ordinary rises in the supply mains voltage
for a 5% increase or decrease in ‘applied voltage
a change of approximately 10% appears at the
ends of the ?lament. It will accordingly be real
ized that the life of the ?lament is jeopardized.
If, in addition to mercury additional metals such
as cadmium and/or zinc are included in the ?lling
and the amount of metal is \such that it is not
- the ?lling is not completely evaporated.
We may furthermore adjust the weights of
10 cadmium and/or zinc relatively to the weight of
completely vapourized at the operating wattage 10
the mercury in the ?lling so that as far as may
or any excess thereof which is likely to occur in
be the voltage drop across the other lamp varies
in the sameratio as the mains voltage varies.
practice the characteristic becomes changed in
that it is no longer ?at topped for the discharge
' The effect of the introduction of additional
path but rising as shown by curve E. Due to
increase in voltage across the discharge path with
increase in current there will not be the great
increase in voltage across the ?lament that is‘
metals in the lamp ?lling will be clear from a con
sideration of the curves shown in Figs. 1 and 2
of the accompanying drawings.
Fig. 1 shows current-voltage characteristic _ shown by curve D but the characteristic for the
curves for two kinds of high pressure discharge
20 lamps.
Curve A is for a mercury vapour lamp
without additional metals in the ?lling in which
all the mercury is vapourized when the lamp is
running. A steep rise will be noted commencing
soon after the point at which the lamp strikes,
25 and when all the mercury is volatiiized the maxi
mum voltage across the lamp is reached and the
curve becomes substantially horizontal showing
that no appreciable change of voltage across the
discharge path takes place with increase of cur
30 rent while the mercury is in a completely va
pourized condition. If there is any increase in
current ?ow there must be an increase in voltage
across the resistance connected in series with the
discharge path and consequent increase in the
35 watts to be dissipated, and the percentage rise
in voltage across the ?lament will be greater than
the percentage increase in applied voltage caus
ing the current increase, the increase in voltage
‘appearing almost entirely across the ?lament.
40' Curve B is a current-voltage characteristic for
a high pressure mercury vapour discharge lamp
with an additional ?lling of metals, e. g. cadmium
and zinc, having a higher boiling point than mer
?lament will take the form shown at F. Any
change in applied voltage .will then appear across 20
the discharge path and across the ?lament in a
ratio determined by the slope of curves E and F.
If curve E be made to correspond closely with
curve F a given percentage change in applied
voltage will produce a like percentage change 25
across the ?lament.
A lighting unit comprising a high pressure va—
pour discharge lamp and a tungsten ?lament lamp
according to the invention will now be described
with reference to Figs. 3, 4 and 5 of the accom_ 30
panying drawings. Figs. 3 and 4 show two views
of such a lamp, the view had in Fig. 4 being that
obtained by looking at Fig. 3 from the right and
Fig. 5 being a plan view of the ?lament projected
from Fig. 4.
The lamps are contained within a glass outer -
envelope l ?tted with a screw cap of known type.‘
Within the envelope l is a discharge lamp 2,
tungsten ?lament 3, bi-metallic thermal switch
4 and the supporting arrangements for the dis
charge lamp and the tungsten ?lament.
discharge lamp 2 is of the kind referred to in
United States application No. 755,989. It has
two main electrodes, each comprising a core of
It will be noticed that during the running up emissive material closely surrounded by a helix' 45
of the lamp the curve rises much less steeply than of tungsten or tantalum wire having its axis at
does curve A and so longas there is unvapourized right angles to that of the discharge lamp, an
metal in the lamp the curve will tend to rise. If auxiliary tungsten. electrode of helical form co
the amount of additional metal in the ?lling is a-xial with that of the lamp surrounding the active
50 such that it is not completely vapourized at a electrode. The wires of the electrodes are joined 50
wattage in excess of the operating wattage that to light rods which are sealed into the ends of
is likely to be encountered the lamp will then be the discharge lamp envelope and the connections
operating on a sloping part of the curve and any
increase in current will be accompanied by an
55 increase in voltage across the discharge path. If
v the ?lling is such as to be completely vapourized
‘ at the operating wattage the curve will assume
the ?at top characteristic of curve A. By a suit
able adjustment of the relative weights of the
60 metal contents a characteristic curve may be had
closely approximating that of a tungsten ?lament
In Fig. 2 are two sets of curves showing how
the voltage varies across the discharge path and
65 across an incandescent tungsten ?lament con
to the wires of the upper electrodes pass from
the seal into the outer envelope l where they are
sealed into the pinch 5 at the capped end of 55
envelope I. Also sealed into the pinch 5 are rods
6 and 1. Rod 6 is connected to a helical ring 0
?tting the inside of the envelope I and surround
ing the discharge lamp near its lower end. The
ring 8 has a stirrup portion 9 depending below 60
the discharge lamp 2 to which are attached the
rods sealed into the lower end of the discharge
lamp and connected to the lower active electrode.
Rod 1 is suitably bent or has a branch "la'con-.
nected to it at the upper end of the outer en 65
nected in_ series with it with changes in applied velope, the part 1a passing down the envelope to
voltage, the voltages being expressed as percent; ' apoint below the ‘discharge lamp where it sup
ages. Curve C shows the change of voltage across ports and leads current to one end of the tungsten
the discharge path of a mercury vapour lamp
70 and it will be, found to have a ?at top overthe
working range in accordance with the character
istic of curve A in Fig. 1. Any rise in applied
voltage produces a change of current‘ through the
lamp and since no appreciable change ‘across the
75 discharge path occurs, the increased voltage ap
?lament 3 the other end of the ?lament 3 being
connected to a rod which acts as a current lead 70
. and a support and which is attached to the stir
mp 9. A further point in the ?lament is con- .
nected by rod III which passesup the outer en
velope and terminates in a glass bead ll. Near
the glass bead it is provided with a contact‘ mem
her I! associated with the thermal switch 4. Rod
1 or a branch thereof is also sealed into the glass
bead H and provided with a contact member
attached to the bi-metallic member of the ther
CI mal switch 4. The tungsten ?lament 3 is sup
ported by radial members sealed into a boss I3
which is centred by supporting members H at
tached to the stirrup 9 and the rods 6 and Ill.
The connections to the upper electrode of the
10 discharge lamp by which the lamp itself is sup
ported are held by a spiral supporting spring l5
which by its tension ?ts the inside of the envelope
l closely and provides a resilient suspension for
the discharge lamp 2. The rod ‘I and a wire con
nected to the active electrode lead l5 are at
tached to the cap terminals, i. e. to the screwed
portion and to a central terminal. Wires con
nected to the auxiliary electrode lead l1 and to
rod 6 are connected to a high resistance contained
within the lamp cap. The sealing pip for the
discharge lamp is made as small as is practicable
and is positioned at the upper end behind the
electrode where it may be kept hot by convection
currents. Both hemi-spherical ends of the dis
charge lamp are preferably coated internally with
a thin metallic coating to assist in the volatili
zation of the metal ?lling by re?ection.
The space between the discharge lamp 2 and
the outer envelope l is exhausted and an inert
gas or gases are introduced so that the ?lament
lies in a gas ?lled envelope and has the properties
of the well known gas ?lled incandescent ?lament
The ?lament contributes red rays which will,
at least to some extent compensate for the lack
of red rays in the spectrum of a mercury ?lled
lamp. Further compensation may be had by the
introduction of other metals such as cadmium
and/or zinc into the discharge lamp and these
40 metals play a further important part in that the
characteristic of the discharge lamp is modi?ed
so that the current volts characteristic, by suit
able adjustment of the weights of the metals can
be made to approximate to that of a gas ?lled
tungsten ?lament lamp with the result. that any
change in the voltage applied to the lighting unit
appears equally across the discharge path and
across the ?lament.
To avoid overloading the ?lament during the
50 running up period of the discharge lamp and yet
permit the ?lament to glow at its rated output
it is arranged that the whole ?lament is con
nected in series with the discharge lamp during
the running up of the latter, the length of ?la
55 ment corresponding to the difference between the
applied voltage and the voltage drop across the
tion of a lamp embodying the invention a lamp
rated at 500 watts will be considered. ‘ The power
factor of such a lamp will be about .94 so that
with 534 volt-amperes and 230 applied volts the
full load current will be 2.32 amperes. The volt
age drop across the discharge path immediately
after the-lamp has been switched on is about 20
so that the total length of ?lament will corre
spond to 210 volts. The voltage across the dis
charge lamp will rise to about 138 and the length 10
of ?lament to be short circuited by the thermal
switch will correspond to this value. The por
tion of ?lament left in circuit will then be oper
ated at its rated efficiency of 14.5 lurnens per
watt calculated to give a life greater than 1500v
hours. There will thus be a watts dissipation of
approximately 200 in the ?lament and 300 in the
discharge lamp.
As regards the metallic ?lling of the discharge
lamp the amount of additional metals will not _
require to be so great as _in the case of the lamp
described in United States application No. 755,989
since the ?lament itself compensates, at least
partially for the lack of red in the mercury spec
trum and the additional metals are mainly intro
duced to bring about the desired slope of the
current volts characteristic curve.
For this pur
pose an amalgam consisting of 1 part by weight
of cadmium, 1 of zinc and 10 of mercury amount
ing to a total weight of .35 gramme, will be found 30
satisfactory. The lamp 2 may have diameter of
38 mm. and a length of discharge of l40'milli
metres. The resistance in the starting circuit
situated in the lamp cap may be 50,000 ohms.
What is claimed is:-- '
1. An electric lighting unit comprising a high
vapour pressure discharge lamp in which the ?ll
ing consists of mercury and an additional metal
having a higher boiling point than mercury, a
tungsten ?lament connected in series with said 40
discharge lamp and situated underneath said dis
charge lamp, a containing vessel enclosing said
discharge lamp and said tungsten ?lament and
?lled with an inert gas at low pressure, and a
thermally operated device situated in said con 45
taining vessel for cutting out a portion of the
said tungstenr?lament when the unit is connected
to supply mains "and. the voltage across the dis
charge lamp approaches closely its working value,
the amount of additional metal in the ?lling of r
the discharge lamp being such as to give the dis
charge lamp when in full working a current
voltage characteristic approximating to that of a
gas-?lled tungsten ?lament lamp.
2. An electric lighting unit comprising a‘ high
pressure discharge lamp having a ?lling consist
ing of an amalgam of mercury, cadmium and zinc,
discharge path.
The bi-metallic thermal switch is situated near a metal ?lament, connected in_ series with said
the top of the discharge lamp so that it is affected discharge lamp, and a thermally operated device
for cutting out a portion of the metal ?lament
almost solely by the heat dissipated by the dis
charge lamp, the heat from the ?lament having when the unit is connected to supply mains and
very little effect. After the discharge isstarted the voltage across the discharge lamp approaches
the bi-metallic member heats up by conduction ‘ closely its working value, the proportions of the
metals in the ?lling of the discharge lamp and
and convection and the switch is so adjusted that
it closes when the normal running up period of their amount being such as to give the discharge
the lamp has expired or is about to expire and lamp when in full working a current-voltage
short circuits a length of the ?lament correspond— characteristic approximating to that of the metal
ing to the voltage drop across the discharge path ?lament connected in series with it.
3. An electric lighting unit comprising a high
so that the remaining portion of the ?lament
glows at its rated output. Owing to a certain vapour pressure discharge lamp having a ?lling 70
amount of thermal lag it is assured that the of mercury and additional metal with a boiling
temperature of the bi-metallic member is still point higher than mercury, a tungsten ?lament
increasing after the voltage across the discharge connected in series with said discharge lamp, a
containing vessel enclosing said discharge lamp
path has become constant.
and tungsten ?lament, and a thermally operated 75
As an example of suitable data for the produc
- 4
device situated within said containing vessel for
cutting out a portion of said ?lament when the
unit is connected to supply mains and the tem
perature within the containing vessel attains a
value indicative of a voltage across the discharge
lamp at which the portion of said ?lament re
maining in circuit may be operated safely, the
additional metal and the relative proportions of
mercury and additional metal being such that the
vapour pressures are lowered to prevent the mer
cury from being completely evaporated at the
said voltage.
4. ‘In an electriclighting unit as set forth in
claim 3, the additional metal being cadmium and
5. In an electric lighting unit as set forth ‘in
claim 3, the additional metal being cadmium and
zinc and the proportions of mercury, cadmium
and zinc being approximately in the order of
10 to 1 to 1;
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