Note: Descriptions are shown in the official language in which they were submitted.
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1~71289 PHN 8327
The invention relates to a mirror condenser lamp
comprising a) a glass lamp vessel having a rotationally
symmetrically curved mirrored wall portion and a rotationally
symmetrically curved transparent wall portion, a cylindrical
wall portion extending from the line of intersection of the
two curved portions, b) a tungsten filament connected to
current supply conductors and arranged in the lamp vessel in
such manner that the filament surrounds the focus of the
mirrored wall portion situated within the lamp vessel, c) a
vacuum-tight seal in the cylindrical portion of the lamp
vessel through which the current supply conductors are passed
to the exterior, and d) an inert gas-containing atmosphere
in the lamp vessel.
Such lamps are known inter alia from our
German Patent Specification 1,023,525 which was published
on October 23, 1958. They are destined for use in sub-
standard film projectors. In order to achieve that the lamps
have a high colour temperature and a high brightness, the
filament is designed so that it has a very high temperature
during operation at design voltage.
In order to shield both the mirror and the
light window of the lamp during the whole life from tungsten
deposition, the known lamps comprise a dome-shaped bulge
which is situated diametrically opposite to the cylindrical
wall portion and in which the tungsten deposition is con-
centrated under the influence of the convection currents.
As a result of the bulkiness of the lamp vessel
of the known lamps and the mechanical weakness associated
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r ~ 1071~89
PHN 8327
therewith, only a low gas pressure can prevail in said lamps.
As a result of this and due to the high temperature of the
filament the life of the known lamps is restricted to 15 to
25 hours.
Not only in sub-standard film projection apparatus,
but also in other apparatus in which light sources are used, for
example reading apparatuses, balances and the like, there is the
tendency towards a more compact construction. With lamps of the
known type it is not possible to follow said tendency.
It is the object of the inventilon to provide mirror
condenser lamps with which the present requirement for miniatur-
isation of apparatuses in which light sources are used, in
particular projection apparatuses, is met and which also have a
longer life at an at least equal filament temperature.
Accordingly, the invention provides a mirror
condenser lamp of the kind mentioned in the preamble which is
characterized in that the gas atmosphere has a pressure of more
than 1 atmosphere and comprises halogen, in that the lamp
vessel consists of a halogen-resistent hard glass having a
softening temperature of at least 500C, and the inside of the
wall of the lamp vessel during operation assumes a temperature
at which tungsten halogen compounds are volatile.
Although it is known that lamps having a tungsten
halogen cycle can be made from halogen-resistent hard glass
(see, for example, the United States Patent Specifications
3,648,094 which issued to Westinghouse Electric ~orp. on March
7, 1972 and 3,829,729 which issued to GTE Sylvania Inc. on
August 13, 1974), all the said lamps, as well as halogen lamps
of quartz glass, have a
P~IN 83,'7
15.2.1977
1C)71Z~9
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cylindrical lamp vessel.
It has now surprisingly been found possible -
to manufacture lamps of the above-described shape deviating
considerably from the cylinder with which it is possible on
the one hand to illuminate the window of sub-standard film
projection apparatuses completely and uniformly, while on
the other hand the inner wall of the lamp vessel neverthe-
less assumes a temperature everywhere at which tungsten
halogen compounds are volatile so that blackening of the
lamp vessel is prevented. The small dimensions of the lamp
which are necessary to reach the required minimum wall
temperature enable high filling pressures to be used as a
result of which the lamps have a longer life and the
filament can be loaded more highly.
In lamps according to the invention the
previously used dome-shaped bulge of the lamp vessel is
superfluous since no place need be provided where tungsten
can deposit without thereby deteriorating the luminous
efficiency of the lamp. In the new lamps such a bulge is
even undesired since the wall of the lamp vessel would
have too low a temperature at that area - the wall
temperature should be at least 200 C at any site - to cause
the halogen/tungsten cycle to take place and since such a
bulge would reduce the ac*ive surface area of the mirrored
wall portion.
Therefore, the line of intersection of the
ourved mirrored wall portion and the curved transparent wall
portion is substantially circular except where the cylindri-
cal wall portion is situated.
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P}IN ~27
15.Z. 1977
1071289
The cylindrical part of the lamp vessel is
preferably chosen to be as short as possible, that is,
not longer than is necessary to be able to realise the
vacuumtight seal of the lamp vessel. As a rule, the length
of the cylindrical portion of the lamp vessel measured
between the circular li-ne of intersection of the curved
wall portions of the lamp vessel and the vacuum-tight seal
will be at most 5 mm.
An advantage of this lamp construction is
- 10 that the current supply wires are led through to the
exterior in a direction transverse to the beam of rays.
As compared with the reflector lamps in which the current
supply wires are led through to the exterior along the
optical axis of the reflector this means a considerable
increase of the effectively reflective surface area.
Lamps according to the invention cannot only
be used in sub-standard film projectors but also for the
projection of 16 mm films and transparencies for microscope
illuminaticn in micro reading apparatus and balances.
~urthermore the lamps may be used as spot lights, bicycle
lamps and moped lamps, signalling lamps and the like.
Lamps for the last-mentioned applications as
a rule have a paraboloidal mirrored-wall portion, whereas
in lamps for the first-mentioned applications said wall
portion usually is curved ellipsoidally. The transparent
wall portion is usually spherical or hyperboloidal.
The lamps according to the invention are
significantly smaller than the said known lamps of the
same power, so that they give the designer of apparatus
ample possibilities as regards extensive miniaturisation.
Pll~ 8327
15.2.1977
10712~9
The diameter of the above-described circular line of
intersection and the largest dimension transverse to the
plane defined by said line are in the lamps as a rule
between 10 and 40 mm.
The lamp vessel is made from halogen-resistent
hard glass having a softening temperature of at least
500 C. As such are to be considered primarily alkali-
alumino-borosilicate glasses having a coefficient of
expansion of 31-37 x 10 7 C at 0-300 C. Said glasses
contain 77-81~ by weight of SiO2, 12-15~ by weight of
B203; 3-5.5~ by weight of Na20 and 1.5-2.5~ by weight
of Al203 and are commercially available inter alia under
the trade ~m~ "Pyrex". For example, a glass as mentioned
~ in the above United States Patent Specification 3,829,729
may also be used.
The lamp vessel may be manufactured, for
example, by heating a glass tube which is closed at one
end and blowing to the desired shape in a mould. An exhaust
tube is preferably provided on~the line of intersection of
t~e two curved wall portions. Although said exhaust tube
can be sealed at the end of the production process so
that the line of intbrsection of the two curved wall
portions excépt for the site where the cylindrical wall
portion is present, is substantially circular, it is
alternatively possible to keep an open exhaust duct in
the seal, for example a pinch seal which is present in
the cylindrical part of the lamp vessel, which exhaust duct
is sealed at the end of the produ~tion process.
~n a simple embodiment the mirrored wall
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l~lN 8327
15.2.1977
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1~71289
portion of the lamp has a metal layer, for example, a layer
of silver or aluminium on the outside. However, it is
alternatively possible for said wall portion to have an
interference mirror so that it reflects visible radiation
and passes thermal ràdiation.
The transparent wall portion may be provided
with a light pervious filter which reflects thermal
radiation. In that case the other curved wall portion may
be provided with a metal layer. When the mirrored wall
portion is curved ellipsoidally, the transparent wall
- portion is preferably curved hyperboloidally.
The foci of the mirrored wall portion and
- the transparent wall portion are preferably made to coincide.
Bromine is to be preferred as a halogen for
the tungsten/halogen cycle. This substance may be dosed as
such, possibly together with hydrogen, or as a compound,
for example, hydrogen bromide or a brominated hydrocarbon.
A lamp of the invention will be described
in greater detail with reference to the figures and the
examples.
Figure 1 is a front elevation of a lamp,
two times enlarged.
- Figure 2 is a longitudinal sectional view
taken on the line II-II.
A hard glass vessel 1 has a curved transparent
wall portion 2 and a curved wall portion 3 which is
provided with a reflecting layer 4. On the line of inter-
section of the two curved wall portions is situated a
cylindrical part 5 terminating in a pinch seal 6. Current
E'IIN 8327
15.2.1977
107~LZ89
conductors 7 and 8 are led through said seal in a vacuum-
tight manner. An exhaust duct 9 is sealed at 10 outside the
pinch seai. The current conductors support a filament 11
~ which surrounds the focus of the curved mirrored wall portion.
Example.
A hard glass tube, outside diameter 8 mm,
- sealed at one end was blown in a mould to form a lamp vessel
for a lamp according to the invention. The wall portion
destined for mirroring was curved ellipsoidally. Half
the long axis of the ellipsoid was 23.4 mm long. Half the
focal distance was 14 mm. The other curved wall portion,
destined to serve as a light window, was curved hyper-
boloidally: half the distance between the branches of the
hyperboloid 8.4 mm, half focal distance 14 mm. The circular
line of intersection of these two curved portions had a
diameter of 30 mm. The largest dimension of the lamp vessel
at right angles to the plane of the circular line of
intersection was 15 mm.
Molybdenum current conductors, diameter
400/um, were provided with a glass bead by fusing a capillary
- (inside diameter 420/um, outside diameter 600/um) on the
conductors. The current conductors were provided with a
tungsten filament after which the assembly was inserted
into the lamp vessel via the cylindrical portion over such
a distance that the coinciding foci of the ellipsoidally
and hyperboloidally curved portions were within the filament.
The longitudinal axis of the filament was arranged at right
angles to the optical axis of t~he lamp vessel. After sliding
a glass tube, in which a metal mandrel was arranged, between
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Pll~' 8327
15.2.1977
10712139
the current conductors into the aperture of the lamp vessel,
the lamp vessel was sealed for the greater part by a
pinching process. After removing the metal mandrel, the
lamp vessel was evacuated via the exhaust aperture and
filled with 3 Torr HBr and 3 atm. krypton, after which
the exhaust aperture was sealed.
The ellipsoidally curved wall portion was
mirrored with silver and then coated with aluminium paint.
The lamp consumed a power of 50 W at 8 V.
The glass used had a composition of 80.5~o by
weight of SiO2, 13~ by weight of B203, 3. 5~ by weight of
Na20, 0. 7% by weight of K20 and 2. 3yo by weight of Al203.
In the figures said lamp is shown two times enlarged.
In a second embodiment the hyperboloidally
curved wall portion was covered on the outside with an
interference filter reflecting thermal radiation and
constructed from 5 pairs of layers of ZnS and MgF2. In
this lamp the exhaust tube seal was positioned on the
substantially circular line of intersection of the
ellipsoidal and the hyperboloidal wall portion, diametrical-
ly opposite to the cylindrical portion of the lamp vessel.
