Note: Descriptions are shown in the official language in which they were submitted.
1 1~7~
PHN 9~136
The invention relates to a discharge lamp compris-
ing a discharge vessel in which xenon and an absorbent which
is in contact with the xenon are present, the xenon being
absorbed at least partly in the absorbent and being releas-
ed partly from the said absorbent when -the temperature is
~ raised.
Such a lamp is disclosed in British Patent Specifi-
cation 669,o33. The xenon pressure in the operating condi-
tion of the lamp described lies in such a range that a
light source having a comparatively large light output can
be realised with it. In the inoperative condition of the
lamp the xenon pressure is reduced by means o~ the absor-
bent. In this known lamp the absorbent is provided in a
holder around the electrode rod. A construction as used
in this known lamp requires the use of` a long electrode
rod. This may be a disadvantage. It is the object of the
invention to provide a construction in which the said
disadvantage is removed or at least mitigated.
According to the invention, a lamp of the kind
20 mentioned in the opening paragraph is characterized in that
the absorbent is present in a cavity in the wall of the
dis~harge vessel.
The lamp according to the invention has the advan-
tage tha-t the presence of the absorbent is independent of
25 electrode rods, and is based on the recognition of the fact
that the wall of the discharge vessel is a suitable place
for storing the absorbent.
It is feasible that the cavity, in the form of a
separate ~ppendix of` the discharge vessel, may be enclosed
30 by -the wall of the discharge vessel. Ilowever, a lamp in
accordance with the inven-tion preferably comprises at least
one lead--through for a current supply member to an internal
electrode and the ca-vity is present at the area of the
~ 1S7gO~
4-12-1979 2 PHN 9436
lead-through. The advantage of this lamp is that space is
obtained for the location of the absorbent by means of a
simple construction.
In a further preferred lamp in accordance with the
inven-tion the lead-through is a metal cup which is located
in the cavity, which cup tightly ~ -s substantially
throughout its length against the wall enclosing the cavity,
said cup being gas-permeable on a side facing the electrode.
The advantage of this lamp is that the absorbent is in a
lO favourable place from a point of view of light-technology.
The wall of the discharge vessel consists, for
example, of quartz glass or a ceramic material. In a fur-
ther advantageous embodiment of a lamp in accordance with
the invention -the lamp of the discharge vessel mainly con-
lS sists of densely sintered aluminium oxide. Such a lamp
has for its advantage that the wall of the discharge vessel
is a good heat conductor. ~s a result of this it is achieved
that the absorbent rapidly assumes a sufficiently high
temperature.
The absorbent may comprise one or more materials,
for example, fine-granular oxides, carbides, borides and
metals. In an improved embodiment of a lamp in accordance
with the invention the absorbent is mainly carbon. This
lamp thus has a material wi-th good absorption properties,
25 which is advantageous.
~ lamp in accordance with the inven-tion ma~ be,
for example, a low-pressure discharge lamp or a high-
pressure mercury vapour discharge lamp. ~ccording to an im-
proved preferred embodiment of a lamp in accordance with
30 the inventio-n, however, the lam-p is a high-pressure soclium
-vapour discharge lamp. The advan-tage of this lamp is a high
luminous flux and good ignition proper-ties.
The invention will now be described in greater
detail wi-th re:terence to a drawing. tn the drawing
~ig. 1 is a side elevation, partly broken away, of
a lamp in accordance with -the invention, and
I!ig. 2 is a sectional vie~ of a detail of a lead-
through construction of the larnp shown in ~ig. 1.
1 15790~
4- 12- 1979 3 PHN 9436
Reference numeral l in Fig. l denotes a discharge
vessel the wall of which consists of densi.ty sintered alu-
minium oxide which is enclosed by an envelope 2 having a
lamp cap 3. The discharge vessel 1 has two internal main
electrodes 4 and 5 between which the discharge is maintained
in the operating condition of -the lamp. Main electrode 4 is
connected to a metal strip 7 via a leadthrough 6. This strip
7 is connected to pole wire 8 which is connected to a con-
tact of the lamp cap 3. An extended portion 9 of the pole
wire 8 serves to support and centre the discharge vessel 1
in the envelope 2. The main electrode 5 is connec-ted to a
strip-shaped conductor 13 by means of a leadthrough con-
sisting of a tubular cup 10 and a rod 12. The other end of
said conductor 13 is connected to another contact in the
lS lamp cap 3. The cup 10 fi;ts tightly in the cavity 35 (Fig.
2) in the vessel wall and is filled with carbon 11 .
Near its end where the tubular cup lO is pre.sent,
the discharge vessel l is surrounded by a heat shield 25
extending the length of the cup. The heat shield preferably
20 consi.sts of tantalum.
The discharge vessel is provided with an ex-ternal
auxiliary elec-trode 20. Near the main electrode 4 said auxi-
liary electrode 20 is connec-ted to the s-trip 7 by a capaci-
tor 23. At the other end of the discharge vessel the auxi-
25 liary electrode 20 is connected to one end of an auxiliarymember 21 in the form of a tension spring. The other end of
the auxiliary member 2 l is connected to the metal strip 13
by means of a conductive strip 22.
Reference numeral l in -l~ig~ 2 again denotes the dis-
30 charge vessel of which is shown the part near the mainelectrode 5. The cup 10, whi.ch together with rod 12 consti.-
tutes the leadthrough to -the electrode 5, consists of
- niobium and fits -tightly in the cavity 35. Before being
provided in the discharge vessel the cup 10 is successively
35 subjected to -the following operations. F`irst the absorbent
11 is placed in the cup. A number of sawcu-ts are then pro-
vided in -the cup at ~ts open side, wh:ich cu-ts extend in the
longi-tudinal d:i.rec-tion of -tlle a.~is of the cup and the
1 ~S790~
4 PH~ 9436
lengths of which are substantially half the diameter of the
cup. The niobium strips lOa thus formed are then folded
inwards and interconnected at their free ends to form a con-
nection point. The main electrode 5 is connected to this
connection point by means of an electrode rod 5a. Herewith
it is achieved that the carbon can be reached by the xenon.
It is also possible for this niobium cup to be covered by
means of a layer consisting of a porous metal.
The lamp described relates to a high-pressure sodium
vapour discharge lamp having xenon as a buffer gas. The
pressure of the xenon at 300 K is approximately 16 kPa. In
the operating condition of the lamp in which the average
temperature is approximately 2200 K, the xenon pressure is
approximately 213 kPa. The niobium cup lO which has a dia-
meter of 4 mm and a volume of approximately 75 mm3 contains45 mg of carbon. The lamp in question is suitable for being
connected to a supply source of 220V, 50 Hz v a a stabili-
sation ballast (not shown) of approximately 0.11 H. In
addition to the stabilisation ballast, a starter (not shown)
is incorporated in the connection to the supply source,
which starter may, for example, be of the type described in
our Canadian Patent 896,070 which issued on ~arch 21, 1972.
The power consumed by the lamp is ~00 W. The luminous flux
is approximately 135 lm/W. The ignition voltage presented
to the discharge vessel is approximately 3 kV.
The lamp of the above described embodiment has a
discharge vessel the wall of which consists of density sin-
tered aluminium oxide. The length of the discharge vessel
is approximately 110 mm and the inside diameter is approxi-
mately 7.5 mm. The distance between the two internal mainelectrodes of the discharge vessel is 82 mm, while the dis-
tance from a main electrode to the nearest end of the dis-
charge vessel is approximately 11 mm. The discharge vessel
has a filling which in addition to xenon ccmprises 25 mg of
amalgam, containing 27% by weight of sodium and 73% by
weight of mercury. The lamp combines good ignition proper-
ties and a high luminous flux with a favourable place for
storing the absorbent.
