High pressure discharge lamp

Details High pressure discharge lamp High pressure discharge lamp

2001-06-25

2002-10-08

Wong, Don (Department: 2821)

Electric lamp and discharge devices: systems

Combined load device or load device temperature modifying...

Electric switch inside evacuated or gas filled envelope

C315S058000

Reexamination Certificate

active

06462477

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a high pressure discharge lamp.
BACKGROUND OF THE INVENTION
High pressure discharge lamps such as a high pressure sodium lamp or a metal halide lamp are widely used for exterior illumination of roads, public squares, sports facilities, etc. or in recent years for exterior illumination of commercial facilities or the like, based on advantageous features that they have a comparatively excellent color rendering property in addition to the merits of high efficiency and high luminance.
In order to light such high pressure discharge lamps, a starter generally is necessary. The starter is classified into two types: an external type incorporated into a lighting ballast and a lamp integrated type incorporated into a lamp itself. The latter lamp integrated type is in widespread use because by combining it with a simple copper iron reactance ballast, the cost of the lamp system is reduced.
Among the conventional built-in starter type high pressure discharge lamps there is one provided with a starter using a ferroelectric ceramic capacitor element with non-linear characteristics. This starter has the merit of high safety in practical use, and the startup performance also is comparatively excellent, so that it is more and more widely spread (See JP5(1992)-87940B, JP5(1992)-290985A).
FIG. 7
shows a conventional example of a built-in starter type high pressure sodium lamp. A starter of this lamp includes a series circuit of a ferroelectric ceramic capacitor (NCC) element
24
connected in parallel to an arc tube
23
of the high pressure sodium lamp and a bilateral semiconductor switching element
25
. The starting operation is as follows.
When a power source
13
is applied, the NCC element
24
performs the operation of so-called current switching by cutting off the current based on its non-linear characteristics. Thereby, in a reactance ballast
14
, a starting pulse voltage of 1500V to 2000V is induced for every half cycle in superposition on a source voltage, and with this voltage, the arc tube
23
is started. In this operation, the semiconductor switching element
25
serves to raise the starting pulse voltage even more by sharpening the current switching operation by the NCC element
24
. In addition, in the configuration shown in
FIG. 7
, a start assisting conductor
28
, which is connected in series to the NCC element
24
and the semiconductor switching element
25
via thermally-actuated switches
26
,
27
, is provided so as to be attached to the arc tube
23
. Through this start assisting effect, the arc tube
23
can be started at a comparatively low starting pulse voltage. After the arc tube
23
has been started, the voltage applied to the NCC element
24
is reduced, and the current switching operation becomes impossible, so that the oscillation of the starting pulse voltage is stopped. Next, due to heat generation of the arc tube
23
after starting, the thermally-actuated switches
26
,
27
made of bimetal elements are operated to be in an OFF state, and the steady lighting of the arc tube
23
is maintained in a state in which the starting circuit part including the NCC element
24
and the semiconductor switching element
25
are cut off from the lighting circuit of the arc tube.
According to the lamp configuration as a completed product, the arc tube
23
and all the starter parts excluding the semiconductor switching element
25
are mounted in an evacuated outer tube glass bulb
29
. The semiconductor switching element
25
is positioned in a base for reducing its temperature. Therefore, for sealing the outer tube glass bulb, instead of an ordinary glass stem used for sealing two lead wires, a glass stem
17
used for sealing an outer tube glass bulb as shown in
FIG. 8A
,
FIG. 8B
is used.
FIG. 8A
is a plane view thereof, and
FIG. 8B
is the front view. In the glass stem
17
, three lead wires
18
,
19
,
20
are sealed.
With regard to the lamp integrated with the starter using the NCC element, two problems related to safety were anticipated to arise during its life time. The first problem is that insulation deterioration of a ballast, a distribution cable, a base socket etc. arises in the case where the lamp becomes incapable of lighting and the starting pulse voltage is continued to be applied. It is dangerous for a human body to touch such a lighting device. The second problem is that in the case where a xenon gas for assisting a start, sodium or mercury filled inside the arc tube leaks from the outer tube glass bulb at the end of life and so on, an arc discharge is induced between the lead wires in the outer tube glass bulb due to the starting pulse voltage, and thus, an overcurrent flows due to this arc discharge. In this case, the ballast will be damaged by fire, or in some cases, the outer tube glass bulb will be broken.
In the starter according to the conventional technique shown in
FIG. 7
, in addition to the basic function of oscillating the starting pulse voltage, the following safety functions are added respectively to solve the two problems mentioned above.
(a) The ferroelectric property showing the non-linear characteristics of the NCC element
24
is maintained in a temperature range of not more than the so-called Curie temperature (normally, about 90° C.). In a temperature range above this, it is changed to the paraelectric property and the non-linear characteristics disappear, and thus, the oscillation of the starting pulse voltage in
FIG. 7
is stopped. In order to solve the first problem mentioned above by applying such temperature characteristics of the NCC element
24
, a heating resistor
30
connected in parallel to the NCC element
24
and the semiconductor switching element
25
is positioned adjacent to the NCC element
24
. Accordingly, even in the case where the arc tube
23
fails to light in spite of the oscillation of the starting pulse voltage, the temperature of the NCC element
24
rises quickly to the Curie temperature or higher by absorbing the heat from the heating resistor
30
in addition to the self heating of the NCC element
24
due to its operation, so that the oscillation of the starting pulse voltage is stopped in a relatively short time.
(b) To solve the second problem mentioned above, first of all, the NCC element
24
itself is designed and constructed to have the so-called self-destructive function. That is, when the starting pulse voltage is applied at the time when a xenon gas etc. leaks, a discharge breakdown occurs due to a creeping discharge between both electrode terminals and so forth, so that the NCC element
24
will be in a conducting state. In addition, a filament coil
31
is connected in series to the NCC element
24
. The filament coil
31
has the so-called fuse function, that is, the filament coil
31
is fused by the flow of an excess current caused by the self-destruction and the conduction of the NCC element
24
. In this way, by combining the self-destructive function of the NCC element
24
and the fuse function of the filament coil
31
, the starter including the NCC element
24
is separated from the lighting circuit and becomes inoperative, so that the starting pulse oscillation is stopped. Even if a power source is applied again, the starter will never operate.
Furthermore, in the starter of
FIG. 7
, to conduct a stable control of the oscillation phase of the starter pulse voltage, a control resistor
32
is connected in parallel to the semiconductor switching element
25
. When the NCC element
24
is used, due to the so-called depolarization at the time of transition from the ferroelectric property to he paraelectric property for every lighting of the arc tube
23
, pyroelectricity flows in the NCC element
24
. To prevent the non-linear characteristics of the NCC element
24
from deteriorating during the lamp life because of this pyroelectricity, a bypassing resistor for allowing the pyroelectricity to flow in a different way needs to be connected in parallel to the NCC element
24
. In the circuit configuration of
FIG. 7

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