JP2729993B2 - How to turn on a neon discharge lamp - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for lighting a high-luminance stable neon discharge lamp suitably used as a light source for line illumination. [Prior art and its problems] For example, as a line illumination light source used in an image scanner or the like, an LED array in which LED elements are arranged in a line or a fluorescent lamp in which mercury is sealed have been used. In order to increase the reading speed of the line illumination, a high-luminance stable light source is required. That is,
A light source satisfying the following conditions is required. (1) Even if there is a large change in the ambient temperature used, the luminance and spectrum hardly fluctuate. (2) High luminance efficiency for electric input and high luminance register. If possible, the brightness of light with a wavelength of 550 nm is 30,
000 nt or more, and light of other wavelengths must have radiance equivalent to this. (3) The lamp is small and lightweight. (4) Brightness should be stable immediately after turning on the electrical input. On the other hand, among the light sources used for the line illumination, the LED array has luminance unevenness in the axial direction illuminated in a line shape and a change in luminance over time after being turned on, These are essential for the LED element and are inevitable. In addition, since high brightness cannot be obtained, there is a problem that high-speed reading cannot be performed.
On the other hand, in a fluorescent lamp in which mercury is sealed, the luminance greatly changes because the vapor pressure of mercury greatly changes depending on the temperature. For example, when the lamp temperature during operation is 30 ° C. or 0 ° C., the luminance changes by about one digit. For this reason, the output of the photoelectric conversion element (for example, a CCD or the like) greatly changes depending on the operating temperature of the fluorescent lamp, which poses a serious problem in image processing. Recently, fluorescent lamps that do not have a temperature dependence of luminance have been developed by encapsulating a rare gas such as xenon gas as a luminous gas without using mercury. The brightness is lower than that of the fluorescent lamp, and a high brightness lamp has not been obtained. As described above, a conventional light source used for line illumination has a low luminance or a large change in luminance depending on temperature, and thus cannot be used as a high-gradation high-speed reading light source. [Object of the Invention] Accordingly, the present invention has been made based on the above circumstances, and an object of the present invention is to provide a method for stably lighting a neon discharge lamp with high luminance. [Structure of the invention and its operation] The lighting method of the neon discharge lamp of the present invention is a method in which a luminous gas mainly composed of neon is sealed inside a long arc tube having a rod shape, the inner diameter of the arc tube is set to 5 mm or less, and luminescence is performed. A neon discharge lamp with a gas filling pressure of 0.5 to 20 Torr is operated at an electric input of 0.5 to 2.5 W per 1 cm of arc length. Usually, a CCD or a Si sensor is used for line reading, and the reading resolution of these is often 10 lines / mm. The irradiation width on the irradiation surface in the line illumination is an extremely narrow width of 1 mm or less. In order to irradiate such a narrow width, it is good to make the tube diameter as small as possible from the viewpoint of light use efficiency. The practical upper limit is about 5 mm in inner diameter. Generally, when the power density (power consumption / arc length) injected between the electrodes is kept constant and the discharge path diameter (the inner diameter of the arc tube) is reduced, the luminance increases. As the size decreases, the loss due to diffusion of ions and electrons into the tube wall in the positive column becomes extremely large, and the luminance efficiency decreases.At the same time, the gas pressure decreases due to electrode sputtering, and the operation time becomes relatively short. Lamp characteristics will change. Accordingly, the present inventors have conducted research and development to increase the luminance of a discharge lamp filled with neon gas that efficiently emits visible light among the rare gases, and to reduce the change in luminance.As a result, the power density was 0.5 to 2.5. When it is in the range of W / cm, the change in luminance due to the fluctuation of the filling pressure of the luminescent gas is small, and when the filling pressure of the luminescent gas mainly containing neon is 0.5 to 20 Torr, high luminance can be obtained. The inventors have found and completed the present invention. That is, when the filling gas pressure is 0.5 to 20 Torr and the lamp is lit at a power density of 0.5 to 2.5 W / cm, even if the discharge lamp has a tube diameter of 5 mm or less,
A light source having high luminance and relatively little luminance fluctuation over a long time can be obtained. Moreover, since a gas reservoir for reducing the decrease in the sealed gas pressure is not required,
A small and lightweight light source lamp can be obtained. And
The neon discharge lamp has the advantage that the luminance hardly fluctuates even when the environmental temperature changes. Further, in order to suppress the lighting voltage and the cathode voltage drop when using the cold cathode, a small amount of argon gas may be mixed into neon gas as penning gas. Also in this case, the spectrum of neon becomes the main component, and the same effect can be obtained. Embodiment An embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 shows a neon discharge lamp used in the present invention,
The two electrodes 2 are arranged opposite to each other near both ends of the arc tube 1 having a long rod shape, and the distance between the two electrodes 2 is the arc length. This arc tube 1
Is composed of a central thin tube portion 11 and expanded portions 12 at both ends. The central thin tube portion 11 is a discharge path, and the inner diameter R is 5 mm.
It is as follows. The electrodes 2 in the enlarged portions 12 at both ends are made of triple carbonate, and leads 3 are connected to the outside of the electrodes 2 so that both ends of the arc tube 1 are hermetically sealed. A luminous gas containing neon as a main component is contained in the arc tube 1.
It is sealed in the range of 5 to 20 Torr, but a small amount of, for example, about 0.05% of argon gas may be added and sealed to improve the lighting property. In a discharge lamp having such a small discharge path diameter and a relatively low luminous gas filling pressure, neon molecules are taken in by the sputtering of the electrode during operation because the number of luminous gas molecules is small, and the luminous gas is gradually discharged. The sealing pressure decreases, and the luminance changes with the pressure decrease. That is, the luminance changes with the lighting time. Therefore, as such a neon discharge lamp having a small discharge path diameter, the inner diameter R of the arc tube 1 is 1.5 mm and the arc length is 260 mm.
Were manufactured, and the relationship between the power density and the luminance was measured using the pressure of the luminescent gas as a parameter. In addition,
The luminescent gas used was a mixed gas of neon and 0.05% argon. FIG. 2 shows the measurement results. As can be seen from the figure, first, as the sealing pressure of the luminescent gas decreases and the power density increases, the brightness tends to increase. However, when the sealing pressure exceeds 20 Torr, the absolute amount of the brightness decreases and the power density increases. The increase in luminance is small even when is increased. Therefore, the sealing pressure needs to be 20 Torr or less. Further, when the power density exceeds 2.5 W / cm, not only the effect of increasing the luminance is reduced, but also the luminance change due to the change in the sealing pressure is increased, and the tube wall temperature of the arc tube is undesirably increased. . Conversely, when the power density is less than 0.5 W / cm, the absolute amount of luminance is insufficient, and the existing reading sensor is insufficient in light amount. After all, the power density is 0.5-
Must be 2.5W / cm. Filling pressure is 20 Torr or less,
When lighting under the condition of power density of 0.5 to 2.5 W / cm, 30,000 nt
The above high luminance can be obtained. Even if the decrease in gas pressure caused by the incorporation of luminescent gas molecules by sputtering becomes 50%, the decrease in luminance can be kept within about 10%. On the other hand, when the incorporation of neon molecules by sputtering is viewed, for example, in terms of the number of atoms that decrease per unit time, the value increases as the sealing pressure decreases. Therefore, in the discharge lamp having a small absolute amount of the luminous gas used in the present invention, the luminous gas is introduced at a high speed by sputtering, and the lamp life may be shortened. Then, the relationship between the filling pressure of the luminescent gas and the lamp life was investigated, and the results are shown in FIG. Here, the lamp life is the time until the luminance is reduced by 30% from the initial use. The used discharge lamp was the same as that used for measuring the relationship between the power density and the luminance described above. The cathode was a cold cathode made of triple carbonate, and the current value was 30 mA. However, as can be seen from FIG. 3, when the filling pressure is 0.5 Torr or more, 4000
The lamp life is longer than an hour, and it does not change much even if the sealing pressure is further increased. However, the lamp life is rapidly shortened at less than 0.5 Torr. Therefore, after all, the sealing pressure needs to be 0.5 to 20 Torr. Next, a discharge lamp having the following specifications was manufactured, and the luminance and the reading speed of the image sensor were measured. Discharge path diameter 1.5mm Arc length 260mm Luminous gas Ne + 0.05% Ar Filling pressure 3Torr Current 15mA Voltage 2.3KV Power density 1.3W / cm When a discharge lamp with such a specification is turned on, the brightness stabilizes immediately after lighting and its value Was 70,000 nt. And
Repeated flashing experiment 200,000 times, brightness decrease 5%
It was about. From this, it is understood that according to the present invention, the neon discharge lamp can be stably lit with high luminance. Next, this lamp was attached to an image scanner with a CCD image reading sensor manufactured by Toshiba, and an experiment for reading an A4 size document was conducted using a lens focusing method. The reading speed was as high as 60 mm / sec.
And, with the same optical system, commercially available red LE made by Stanley Electric
The CCD output was the same as the speed of 15 mm / sec when using the D array. [Effects of the Invention] As described above, the lighting method of the neon discharge lamp of the present invention is such that electrodes are arranged opposite to both ends of an arc tube, and a thin tube portion having an inner diameter of the arc tube of 5 mm or less is provided as a discharge path, A neon discharge lamp with a luminous gas filling pressure of 0.5 to 20 Torr is turned on at an electric input of 0.5 to 2.5 W per arc length of 1 cm, so it is small and light, has high brightness, is stable immediately after lighting, and is sputtered. Therefore, even if the gas pressure is reduced, the decrease in luminance is small and the life is long. Further, there is an advantage that the luminance hardly fluctuates even when the environmental temperature changes. Therefore, according to the present invention, a neon discharge lamp can be stably lit with high luminance, and can be applied to a high-gradation, high-speed reading light source in line illumination.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a neon discharge lamp, FIG. 2 is a diagram showing the relationship between the sealing pressure of a luminous gas, power density and luminance, and FIG. 3 is a diagram showing the relationship between the sealing pressure and the lamp life. . 1 ... Emission tube, 11 ... Narrow tube part, 12 ... Expansion part 2 ... Electrode, 3 ... Lead

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Claims (1)

(57) [Claims] A neon discharge lamp in which a luminous gas containing neon as a main component is sealed in a long arc tube having a rod shape, the inner diameter of the luminous tube is 5 mm or less, and the luminous gas sealing pressure is 0.5 to 20 Torr, has an arc length of 1 cm. 0.5 ~ 2.5W per electric input
A method for lighting a neon discharge lamp, characterized in that the lighting is performed by a light source.