High-intensity discharge lamp

Details High-intensity discharge lamp High-intensity discharge lamp

2001-12-20

2003-05-13

Nguyen, Hoang (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

06563268

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a high-intensity discharge lamp with a built-in starter.
BACKGROUND OF THE INVENTION
In this energy-saving era, as high-intensity discharge lamps for outdoor use such as in streets, public squares, avenues, or for indoor use such as in factories, sports arenas, and shops, metal halide lamps and high-intensity sodium lamps are used because they are more efficient and provide better color rendering in a comparison with conventionally-used high-intensity mercury lamps.
Since these metal halide lamps and high-intensity sodium lamps are applied in general to conventional facilities that have been used for conventional high-intensity mercury lamps, the lighting requires a simple copper-iron type reactance ballast based on the power supply frequency. Therefore, for the purpose of lighting by means of the copper-iron type reactance ballasts, these lamps contain starting circuits that are not provided for conventional high-intensity mercury lamps.
Various types of starting circuits have been used depending on the lamps, which are classified in general into the following two basic types.
An example of a first basic type is shown as a starting circuit
57
in FIG.
6
. The circuit has a basic structure of a series circuit comprising a switching element
58
for interrupting current, a resistor
59
for restricting current, and a thermally-actuated switch
60
composed of a bimetal for disconnecting the starting circuit. This series circuit is connected in parallel to an arc tube
63
comprising at both the terminals a pair of main electrodes
61
and
62
.
The aforementioned starting circuit
57
and the arc tube
63
are arranged inside a glass outer tube
65
that is under vacuum or filled with a gas so as to compose a lamp
64
. The switching element
58
can be, for example, a glow starter for a metal halide lamp, a nonlinear ceramic capacitor or a thermally-actuated switch of a bimetal for a high-intensity sodium lamp. The thermally-actuated switch functions also for disconnecting the starting circuit.
The bimetal thermally-actuated switch
60
for disconnecting the starting circuit, as shown in
FIG. 7
, comprises a lead
66
as a fixed contact, an insulating glass
67
, a supporter
68
as a L-shaped fixed electrode member, a contact rod
69
as a movable contact, and a bimetal plate
70
as a movable electrode member. The lead
66
is connected at one terminal to the electrode
61
and connected at the other terminal to the insulating glass
67
. The supporter
68
is connected at one terminal to the insulating glass
67
and connected at the other terminal to the resistor
59
. The bimetal plate
70
is provided with the contact rod
69
at the front end portion while the back end portion is attached to the supporter
68
. The contact rod
69
contacts with and/or separates from the lead
66
due to slow turn-over operation of the bimetal plate
70
caused by heat. A portion that the fixed contact of the thermally-actuated switch
60
contacts with the movable contact, i.e., a contact between the lead
66
and the contact rod
69
, is positioned to be exposed to the interior of the outer tube
65
.
The starting circuit
57
operates in the following manner. When the switching element
58
repeats on-off operation by application of a supply voltage
22
, a high voltage pulse ranging from 1 kV to 4 kV is induced at a reactance ballast
21
due to interruption of current at every time of on-off operation, thereby causing the arc tube
63
to start discharging. Subsequently, the on-off operation of the switching element
58
stops just after the discharging starts. About two to three minutes after the start of the discharging, the thermally-actuated switch
60
shifts slowly from a closed state to an open state by the heat from the arc tube
63
, and thus, the starting circuit
57
is disconnected from a lighting circuit. Subsequently, the thermally-actuated switch
60
maintains its open state during the steady lighting state of the lamp.
Regarding the starting circuit
57
in
FIG. 6
, a typical metal halide lamp using a glow starter for the switching element
58
is provided with a resistor
59
arranged in the vicinity of the thermally-actuated switch
60
, so that the thermally-actuated switch
60
shifts from a closed state to an open state due to heat from the resistor
59
so as to stop the switching operation of the glow starter in case of a starting failure of the arc tube.
A second basic type is exemplified as a starting circuit
71
in FIG.
8
. Such a circuit is used particularly for a metal halide lamp
76
using a quartz arc tube
75
comprising an auxiliary electrode
74
as well as a pair of main electrodes
72
,
73
. This starting circuit
71
comprises a series circuit including a resistor
77
for restricting current and a thermally-actuated switch
78
of a bimetal for disconnecting the starting circuit. The starting circuit
71
is connected at one terminal to the main electrode
72
and to the auxiliary electrode
74
at the other terminal. Also for this thermally-actuated switch
78
, the contact is positioned to be exposed to the interior of the outer tube
79
.
The starting circuit
71
operates as follows. When a supply voltage
22
is applied, auxiliary discharge occurs first between the main electrode
73
and the auxiliary electrode
74
. Next, due to the action of initial electrons sufficiently supplied from the auxiliary discharge, main discharge starts between the main electrodes
72
and
73
. About two minutes after the start of the main discharge, the thermally-actuated switch
78
shifts slowly from a closed state to an open state by heat from the arc tube
75
, and the starting circuit
71
is disconnected from the lighting circuit. Subsequently, the thermally-actuated switch
78
maintains its open state during the steady lighting state of the lamp.
Some kinds of metal halide lamps use the above-mentioned two basic types of starting units together.
However, it has been known through a long-time use on the market that in the metal halide lamps and the high-intensity sodium lamps containing such conventional starting circuits, especially the above-mentioned two basic types of starting circuits, problems will be caused in connection with thermally-actuated switches for a basic components of such lamps, which are used for disconnecting starting circuits.
As mentioned above, the thermally-actuated switch
60
or
78
comprising a bimetal used for such a conventional starting circuit
57
or
71
has exposed contacts, since such a structure is cost-effective and problems like oxidation are not caused as the contacts are housed in an outer tube.
In a lamp using such a thermally-actuated switch
60
or
78
, especially when the arc tube
63
or
75
fails to start or it ceases its lighting at the end of life etc. due to rise in the lamp voltage, arc discharge can occur, even though the possibility is low, at a contact of the thermally-actuated switch
60
or
78
in an OFF state, i.e., an open state. This is caused by a high voltage pulse induced at the reactance ballast
21
due to current interruption. Here, the problem is that the initial electrons supplied from the arc discharge at the contact can induce sustained occurrence of further arc discharge between a pair of leads that hold the arc tube. Because of the sustained arc discharge, excessive lamp short-circuit current may run continuously in the reactance ballast
21
. Moreover, terminals of the outer tube
65
or
79
facing a lamp base may be damaged although the possibility is low as well.
While an outer tube of a typical high-intensity sodium lamp is in a vacuum state as mentioned above, materials such as sodium as a luminescent material and a xenon gas for a starting aid may leak from the interior of the arc tube at the end of the lamp life. Experimental results show that this causes the above-mentioned sustained arc discharge. Arc discharge can occur at the contact of the thermally-actuated switch
78
of the second type starting c

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