JPH08111206A - Metal halide lamp - Google Patents

Abstract

PURPOSE: To prevent the generation of crack in a sealing part by relaxing the temperature rise of an electrode rod immediately after starting. CONSTITUTION: An arc tube 1 is made up of quartz and comprises a light emitting part 2 having the inner diameter of 2.7mm and a pair of electrodes 7 therein and sealing parts 4 provided on both sides of the light emitting part 2 for sealing introduction foil 3 to which the electrodes 7 are connected. In the inner part of the light part 2, mercury, halogenide such as ScI3 and NaI and a starting gas such as xenon are filled. In the sealing parts 4, the introduction foil 3, for instance, electrode rods 5 connected to molybdenum foil and electrodes 7 comprising coils 6 fixed to the electrode rods 5 are sealed. The end surface of the electrode rods 5 projects from the tip surface of the coils 6, and when the diameter of the electrode rods is D (mm), the weight of the coils is W (mg), a lamp current at a stable period of time is Ir (A) and a lamp current at the time of starting is Is (A), 3<Is/Ir<8 and 2<W/D<7 are satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a metal halide lamp.

[0002]

2. Description of the Related Art Metal halide lamps have been attracting attention as light sources with high brightness and high efficiency. With the development of small and high color rendering metal halide lamps, their usage has expanded.Recently, the development of using such metal halide lamps as a backlight for projection type liquid crystal projectors and a light source for automobile headlights has been promoted. ing.

A metal halide lamp utilizes the emission spectrum of a metal due to discharge in a metal vapor at a high temperature. Therefore, the rated amount of light cannot be obtained until the metal becomes vapor, that is, until the arc tube reaches a certain high temperature. Generally, it takes several minutes from the start of lighting until the rated light amount is reached.

As the use of metal halide lamps has expanded, there has been an increasing demand for improvement in the rise of light output.

In order to speed up the rise of the light output, it has been conventionally known to combine a metal halide lamp with a choke type ballast to turn it on. In this case, the current at the time of starting is only about twice the current at the time of stable.
Also, in order to speed up the rise of the light output as well, instead of the choke type ballast, an electronic lighting circuit with a current control function at the time of starting is used, and a current several times that at the time of stable lighting is made to flow at the time of starting the arc tube. A method of rapidly heating is used.

[0006]

According to the method in which the arc tube is warmed abruptly at the time of starting by supplying several times as much current as during stable lighting, the light output rises quickly, but the arc tube is rapidly warmed. Therefore, there is a problem that cracks are generated in the sealed portion while the heating and cooling by turning on and off are repeated.

This phenomenon occurs because, especially when a large current flows immediately after starting, the electrode rod located inside the sealing portion and the quartz glass are rapidly heated first, and then this electrode rod is heated. Is transferred to the quartz glass around the electrode rod, and the temperature of the quartz glass rises. That is, before the quartz glass is heated and expanded, the electrode rod expands due to a rapid temperature rise, so that the quartz glass is cracked.

The present invention has been made to solve such a problem, and suppresses the occurrence of cracks in the sealing portion by alleviating the expansion of the electrode rod immediately after starting due to the rapid temperature rise. The purpose is to provide a metal halide lamp capable of

[0009]

A metal halide lamp according to the present invention has a pair of electrodes inside, a light emitting portion in which mercury and a metal halide are enclosed, and a light emitting portion connected to both ends of the light emitting portion. A quartz arc tube having a sealing portion that seals an introduction foil connected to the electrode, wherein the electrode is composed of an electrode rod and a coil fixed to the electrode rod, and a tip of the electrode rod. Project from the tip of the coil, the electrode rod diameter is D (mm), and the coil weight is W (m
g), assuming that the stable lamp current is Ir (A) and the starting lamp current is Is (A), 3 <Is / Ir <
It has a configuration satisfying 8 and 2 <W / D <7.

[0010]

With this structure, the heat capacity of the coil is optimized and the temperature rise of the entire electrode immediately after starting is reduced. In addition, the transition to arc discharge becomes easy. Further, during stable lighting, an arc spot is formed on the tip end surface of the electrode rod protruding from the tip end surface of the coil, so that stable arc discharge can be obtained.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, an arc tube 1 of a metal halide lamp for a motor vehicle headlamp having a rated power of 35 W, which is an embodiment of the present invention, includes a light emitting section 2 having a pair of electrodes 7 therein.
The light emitting portion 2 is composed of a sealing portion 4 which is connected to both ends of the light emitting portion 2 and seals an introducing foil 3 to which electrodes 7 are connected. Arc tube 1
Is made of quartz and has a light emitting portion 2 having an inner diameter of 2.7 mm. Inside the light emitting section 2, mercury, ScI ₃ , NaI as a metal halide, and xenon as a starting gas are enclosed. The sealing portion 4 has an electrode rod 5 connected to the introduction foil 3, for example, molybdenum foil, and the electrode rod 5
An electrode 7 composed of a coil 6 fixed to the above is sealed. The tip surface of the electrode rod 5 projects from the tip surface of the coil 6.

Further, in the metal halide lamp of this embodiment, the stable lamp voltage is 85V, the lamp current Ir is 0.41A, and the stable luminous flux is 3000 lumens.

In the lamp structure shown in FIG. 1, an electrode rod diameter D was set to 0.25 mm, and a coil weight W (mg) was changed in six steps as shown in (Table 1) to manufacture a trial metal halide lamp.

The electrode rod diameter D (mm) was selected based on the stable current. The length of protrusion from the coil end surface to the electrode rod end surface was 0.5 mm.

[0016]

[Table 1]

First, for each of the prototype lamps described above,
When the lamp current Is at the time of starting was made to flow twice to 10 times as much as the lamp current Ir at the time of stable and the rise of the light output at the time of starting was confirmed, the rise of the light output at the time of less than 2 times was lit by the conventional choke type ballast. However, devitrification was confirmed on the inner surface of the arc tube quartz in a short time because of an overload when it exceeded 8 times. Therefore, the lamp current Is at the start is
It was confirmed that the range of 3 to 8 times the stable lamp current Ir, that is, Is / Ir is preferably 3 to 8.

Next, the lamp current Is at the time of starting was increased by 6 times which is within the above-mentioned range, and the life test of five prototype lamps was conducted. Target life is 5 per hour
Flashed twice and set the lighting time to 2000 hours. The results of the life test are shown in (Table 2).

[0019]

[Table 2]

As is clear from Table 2, it was confirmed that in a metal halide lamp having a ratio (W / D) of the weight of the coil to the diameter of the electrode rod of 2 or more, no crack was generated even after 2000 hours of lighting. This is because the optimized heat capacity of the coil moderates the sudden temperature rise of the entire electrode immediately after starting.

However, in a lamp having a ratio of the coil weight to the electrode rod diameter of more than 7, cracks did not occur during lighting for 2000 hours, but the arc spot was not stable during stable lighting, resulting in unstable discharge. This is because the heat capacity of the entire electrode becomes too large, so that the entire electrode does not warm up to a sufficient temperature, and a stable arc spot cannot be formed at the tip of the protruding electrode rod 5. When the ratio of the coil weight to the electrode rod diameter is 7 or less, the arc spot during stable lighting is stable at the protruding electrode tip. Further, when the ratio of the weight of the coil to the diameter of the electrode rod was less than 2, cracking occurred during lighting for 2000 hours.

Therefore, in order to obtain a stable arc discharge without causing cracks, the ratio of the coil weight to the electrode rod diameter, that is, W / D is preferably in the range of 2 to 7.

Further, since the tip of the electrode rod is projected from the coil, if it is within this range, the stable arc spot is stabilized at the tip of the electrode rod, so that stable arc discharge can be obtained.

Similar results were obtained for a metal halide lamp having a rated power of 250W.

[0025]

As described above, the metal halide lamp of the present invention has a pair of electrodes inside and a light emitting section in which mercury and a metal halide are enclosed, and is connected to both ends of the light emitting section. And a quartz arc tube having a sealing portion that seals an introduction foil connected to the electrode, the electrode including an electrode rod and a coil fixed to the electrode rod. Has a tip protruding from the tip of the coil, the electrode rod diameter is D (mm), and the coil weight is W (m
g), assuming that the stable lamp current is Ir (A) and the starting lamp current is Is (A), 3 <Is / Ir <
By satisfying 8 and 2 <W / D <7, it is possible to alleviate the expansion of the electrode rod due to the rapid temperature rise immediately after the start and suppress the generation of cracks in the sealing portion.

[Brief description of drawings]

FIG. 1 is a partially cutaway front view of an arc tube of a metal halide lamp according to an embodiment of the present invention.

[Explanation of symbols]

 1 luminous tube 2 luminous part 3 introduction foil 4 sealing part 5 electrode rod 6 coil 7 electrode

Claims (1)

[Claims] 1. A light emitting part having a pair of electrodes inside and containing mercury and a metal halide sealed with an introduction foil connected to both ends of the light emitting part and connected to the electrodes. A quartz arc tube having a sealed portion, wherein the electrode comprises an electrode rod and a coil fixed to the electrode rod, the tip of the electrode rod protruding from the tip of the coil, The rod diameter is D (mm) and the coil weight is W (m
g), when the stable lamp current is Ir (A) and the starting lamp current is Is (A), 3 <Is / Ir <8 2 <W / D <7 is satisfied. Metal halide lamp that does.