JPS60167251A - Metal halide lamp - Google Patents

Abstract

PURPOSE:To achieve increased luminous intensity in the infrared region by using a cesium halide and a sodium halide as metal halides and specifying the amounts of these halides charged in the emission tube. CONSTITUTION:An emission tube 1 for a metal halide lamp contains elctrodes 2 and 3 and is charged with mercury, a rere gas and a cesium halide and a sodium halide which are metal halides. The amounts of the sodium halide and the cesium halide charged are restricted to be at least 2-12mg and 0.4mg per cm<2> internal volume of the emission tube 1 respectively. Therefore sodium atoms is not ionized because its ionization voltage is higher than that of cesium atom.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an improvement of a metal halide lamp characterized by emission in the infrared region.

(Background of the invention) Usually, metal halide lamps are
It is used in the lighting field as described in the publication.

The present inventors have attempted to use this lamp, particularly a metal halide lamp that emits light in the infrared region, as a light source for optical character reading or figure recognition.

Therefore, in the infrared region (wavelength 800 to 900 nm)
Hg in the arc tube as a metal halide lamp that emits light with
In addition to rare gases, I tried to fabricate a lamp using cesium iodide as gold halide. However, this cesium iodide decomposes into cesium and iodine in the arc, but because the ionization voltage of cesium is low, the cesium atoms are ionized and become neutral cesium that emits in the infrared region (800-900 nm). There are fewer atoms. Therefore, there is a problem in that the emission intensity of such a lamp in the infrared region does not increase significantly even if the input is increased, and some kind of countermeasure has been desired.

[Purpose of the invention]

Therefore, one object of the present invention is to provide a metal halide lamp that has a sufficiently large emission intensity in the infrared region.

[Summary of the invention]

In order to achieve the above object, the present invention is characterized in that a metal halide lamp is constructed by adding sodium halide in addition to cesium halide as the metal halide to be sealed, and specifying the amount of these to be filled.

With this characteristic configuration of the present invention, a metal halide lamp with extremely high emission intensity in the infrared region could be obtained.

[Embodiments of the invention]

First, the principle of the present invention will be described.

In the present invention, by enclosing cesium iodide and sodium iodide, both sodium iodide and cesium iodide decompose into their respective atoms in the arc, but the ionization voltage of sodium atoms is lower than that of cesium atoms. Because of its high temperature, it hardly ionizes, which makes it possible to efficiently emit the higher-order spectrum of neutral sodium atoms in the infrared region (820 nm).

The optimal amount of sodium halide is the inner volume of the arc tube 1
2 to 12 mg/cm", and the optimum loading amount of cesium halide is likewise at least 0.4 mg, preferably 0.4 to 2.4 mg.

The reason for this is that the amount of sodium halide enclosed is 2 mg
If it is less than /cm3, the sodium vapor pressure will not be sufficiently high, and as a result, the luminescence in the visible region will be strong, but the luminescence in the infrared region will be small, which is not preferable.

If this amount exceeds 12 mg/cm3, the unevaporated sodium in the filled sodium will become liquid and cover the inner wall of the tube during lighting, which will have a significant negative impact on the lamp life characteristics. So I don't like it.

In addition, the amount of cesium halide enclosed is 0.4 mg/cm
If the value is less than 3, cesium atoms ionized in the arc will diffuse toward the wall, resulting in a shortage of cesium atoms at the center of the arc, making it impossible to effectively cover the arc current.As a result, excited sodium atoms that emit light in the infrared region will also It is not preferable because it is ionized and the luminescence of sodium in the infrared region is suppressed. and.

Even if the enclosed amount exceeds 2.4 mg/am3, the emission intensity in the infrared region is already saturated, so there is no effect, and the expensive cesium halide is wasted.

Next, the present invention will be explained in detail using examples.

FIG. 1 shows an arc tube of a metal halide lamp according to the present invention. In the figure, electrodes 2 and 3 are hermetically sealed at both ends of a quartz arc tube 1. Appropriate amounts of mercury and rare gas are sealed in the arc tube 1, and 8 mg/cm of sodium iodide is added as the sealed metal halide 4.
3. 1.4mg/cm" of cesium iodide is enclosed.

Now, for comparison, in addition to the starting rare gas and mercury, the quartz arc tube 1 contains 8 ml of gas per 1 cm3 of internal volume of the arc tube 1.
A lamp containing only mg of sodium iodide was made,
Its infrared emission spectrum was measured. The result is the second
This is shown by curve A (solid line) in the figure. Curve B (dashed line) in the figure shows the emission spectrum of a lamp in which only 1.4 mg/cm3 of cesium iodide was filled instead of sodium iodide. The emission spectrum of the above-mentioned lamp according to the present invention is as shown by curve C in FIG. 3 with respect to these lamps made of an alkali metal halide alone. Curve C in Figure 3
When compared with curves A and B in FIG. 2, it can be seen that the output in the infrared region has increased from both of them. This is because the enclosed sodium iodide and cesium iodide decompose in the arc, and most of the cesium atoms with low ionization voltage are ionized, and the number of neutral atoms that emit light in the infrared region (800 to 900 nm) is reduced. This is because sodium atoms hardly ionize, and therefore, the higher-order spectrum of neutral sodium atoms is efficiently emitted in the infrared region (820 nm). Therefore, by further increasing the amount of cesium iodide sealed and increasing the lamp input to raise the wall surface temperature of the arc tube 1, the cesium atom density can be increased, and at the same time the sodium emits light in the infrared region, the cesium emits light in the infrared region. It is also possible to increase luminescence. However, if the input power is increased too much, the load on the tube wall of the lamp will inevitably increase, which will significantly shorten the lamp life, which is not preferable. For this reason, it is usually best to design the tube wall load to be 10-15 W/cm2.

In addition, although iodine was described as a halogen element in the above-mentioned embodiment, it goes without saying that other elements may be used. Furthermore, although the combination of sodium halide and cesium halide has been described as the metal halide to be encapsulated, it goes without saying that other metal halides may be encapsulated in addition to these.

〔Effect of the invention〕

As described above, the present invention makes it possible to provide a metal halide lamp having a large emission intensity in the infrared region, which is ideal as a light source for reading characters and graphics.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an arc tube of a metal halide lamp according to the present invention, and FIGS. 2 and 3 are graphs showing the effects of the metal halide lamp according to the present invention shown in FIG. 1... Quartz arc tube, 2, 3... Electrode, 4... Enclosed metal halide Figure 1

Claims (1)

[Claims] 1. Electrodes are sealed at both ends, and mercury is included as a filler.
In a lamp having an arc tube in which at least a halide of sodium and cesium is sealed in addition to a rare gas, the amount of the sodium halide enclosed is 2 to 12 mg per 1 cm3 of the internal volume of the arc tube, and A metal halide lamp characterized in that the amount of filling is at least 0.4 mg per 1 cm' of internal volume of the arc tube.