A rare gas discharge fluorescent lamp device

Abstract: The lamp device basically comprises a rare gas discharge fluorescent lamp (8) wherein rare gas is enclosed in the inside of a glass bulb (1) which has a fluorescent layer (2) formed on an inner face thereof and has a pair of electrodes (3) at the opposite ends thereof. It further comprises a high-frequency ac power source (19) and an electric voltage generating means to generate pulse-like voltage across a pair of electrodes (3) of the lamp (8) wherein an energization time of the puls-like voltage is equal to a half period of a wave form applied from ac power source (19) and the idle time integral-number times as long as the half period of the wave form applied from the ac power source (19).

Description: The present invention relates to a rare gas discharge fluorescent lamp device for use with an information device such as a facsimile, a copying machine or an image reader. In recent years, the performances of information terminal devices such as a facsimile, a copying machine and an image reader have been improved together with advancement of the information-oriented society, and the market of such information devices is rapidly expanding. In developing information devices of a higher performance, a light source unit for use with such information devices is required to have a higher performance as a key device thereof. Conventionally, halogen lamps and fluorescent lamps have been employed frequently as lamps for use with such light source units. However, since halogen lamps are comparatively low in efficiency, fluorescent lamps which are higher in efficiency are used principally in recent years. However, while a fluorescent lamp is high in efficiency, it has a problem that characteristics thereof such as an optical output characteristic vary in accordance with a temperature since discharge from vapor of mercury is utilized for emission of light. Therefore, when a fluorescent substance is used, either the temperature range in use is limited, or a heater is provided on a wall of a tube of the lamp in order to control the temperature of the lamp. However, development of fluorescent lamps having stabilized characteristics are demanded eagerly for diversification of locations for use and for improvement in performance of devices. From such background, development of a rare gas discharge fluorescent lamp which makes use of emission of light based on rare gas discharge and is free from a change in temperature characteristic is being proceeded as a light source for an information device. Figs. 13 and 14 show an exemplary one of conventional rare gas discharge fluorescent lamp devices which is disclosed, for example, in Japanese Patent Laid-Open No. 63-58752, and wherein Fig. 13 is a constructional view showing a transverse section of a rare gas discharge fluorescent lamp and an entire construction of the device, and Fig. 14 is a vertical sectional view of the lamp. Referring to the figures, reference numeral 1 denotes a bulb in the form of an elongated hollow rod, which is made of quartz or hard or soft glass. A fluorescent layer 2 is formed on an inner face of the bulb 1, and rare gas X consisting of at least one of xenon, krypton, argon, neon, helium and so forth is enclosed in the bulb 1. A pair of inner electrodes 3a and 3b having different polarities from each other are located at the opposite end portions within the bulb 1. The inner electrodes 3a and 3b are individually connected to a pair of lead wires 4 which extend in an airtight condition through walls of the end portions of the bulb 1. Further, an outer electrode 5 in the form of a belt is provided on an outer face of a side wall of the bulb 1 and extends in an axial direction of the bulb 1. The inner electrodes 3a and 3b are connected by way of the lead wires 4 to a high frequency inverter 6 serving as a high frequency power generating device, and the high frequency inverter 6 is connected to a dc power source 7. Then, the outer electrode 5 is connected to the high frequency inverter 6 such that it may have the same polarity as the one inner electrode 3a. Operation is described subsequently. With the rare gas discharge fluorescent lamp device having such a construction as described above, if a high frequency power is applied across the inner electrodes 3a and 3b by way of the high frequency inverter 6, then glow discharge will take place between the inner electrodes 3a and 3b. The glow discharge will excite the rare gas within the bulb 1 so that the rare gas will emit peculiar ultraviolet rays therefrom. The ultraviolet rays will excite the fluorescent layer 2 formed on the inner face of the bulb 1. Consequently, visible rays of light are emitted from the fluorescent layer 2 and discharged to the outside of the bulb 1. Meanwhile, another rare gas discharge fluorescent lamp is disclosed as an example in Japanese Patent Laid-Open No. 63-248050. The lamp employs such a hot cathode electrode as disclosed, for example, in Japanese Patent Publication No. 63-29931 in order to eliminate the drawback of a cold cathode rare gas discharge lamp that the starting voltage is high. The rare gas discharge fluorescent lamp can provide a comparatively high output power because its power load can be increased. However, it can obtain only a considerably low efficiency and optical output as compared with a fluorescent lamp based on mercury vapor. However, conventional rare gas discharge fluorescent lamps cannot readily attain a sufficiently high brightness as compared with fluorescent lamps employing mercury because fluorescent substance is excited to emit light by ultraviolet rays generated by rare gas discharge, and therefore, a rare gas discharge fluorescent lamp in high efficiency has been awaited. Further, since a conventional lamp adopts a hot cathode electrode, an extra power supply for preheating the cathode electrode should be unnecessary. A rare gas discharge fluorescent lamp device of the general kind contemplated here and comprising a rare gas discharge fluorescent lamp, wherein rare gas is enclosed in the inside of a gas bulb, which has a fluorescent layer formed on an inner face thereof and has a pair of electrodes at the opposite ends thereof, one of which is a cathode, is also known from DE-OS 32 31 939. It is an object of the present invention to provide a rare gas discharge fluorescent lamp device causing a rare gas discharge fluorescent lamp to light in a higher brightness and with a higher efficiency in comparison with devices of prior art. This object, in accordance with the present invention, is achieved by a rare gas discharge fluorescent lamp device with the features of claim 1. Advantageous embodiments are subject matter of claims 2 to 6. A rare gas discharge fluorescent lamp device according to an embodiment of the present invention is constituted in such a form to attain the same object that it comprises a rare gas discharge fluorescent lamp wherein rare gas is enclosed in the inside of a glass bulb which has a fluorescent layer formed on an inner face thereof and as a pair of electrodes at the opposite ends thereof, a high frequency power source for supplying frequency higher than 3 KHz but lower than 200 KHz, and an electric voltage generating means for applying pulse-like voltage across a pair of electrodes of the rare gas discharge fluorescent lamp, the pulse-like voltage having a period divided into an energization time and an idle time such that the energization time is equal to a half period of a wave form applied from the power source and the idle time is odd-number times as long as the half period of the wave form applied from the power source, wherein the electric voltage generating means comprises a switching element, a control means for controlling the switching element, and two diodes whose polarities are contrary to each other and respectively connected to the rare gas discharge fluorescent lamp in parallel, and wherein one of the two diodes is serially connected to the switching element. A rare gas discharge fluorescent lamp device according to a further embodiment of the present invention is constituted in such a form to attain the same object that it comprises a rare gas discharge fluorescent lamp wherein rare gas is enclosed in the inside of a glass bulb which has a fluorescent layer formed on an inner face thereof and has a pair of electrodes at the opposite ends thereof, a high frequency power source for supplying frequency higher than 3 KHz but lower than 200 KHz, and an electric voltage generating means for applying pulse-like voltage across a pair of electrodes of the rare gas discharge fluorescent lamp by alternatively changing respective polarities, the pulse-like voltage having a period divided into an energization time and an idle time such that the energization time is equal to a half period of a wave form applied from the power source and the idle time is integral-number times as long as the half period of the wave form applied from the power source, wherein the electric voltage generating means comprises two switching elements, two control means for respectively controlling the two switching elements, and two diodes whose polarities are contrary to each other and respectively connected to the rare gas discharge fluorescent lamp in parallel, and wherein the two diodes are serially connected to the respective switching elements. Further, since a rare gas discharge fluorescent lamp device according to one embodiment is constructed such that a pulse-like voltage generating means supplies a pulse-like voltage across a pair of electrodes of the rare gas discharge fluorescent lamp wherein an energization time of the pulse-like voltage is equal to a half period of a wave form applied from the power source and the idle time is odd-number times as long as the half period of the wave form applied from the power source, the probability that molecules of the enclosed gas may be excited at such an energy level that they may emit much resonant ultraviolet rays of the rare gas which contributes to emission of light can be increased, so that the optical output and efficiency of the lamp are improved. Furthermore, since a rare gas discharge fluorescent lamp device according to the further embodiment of the present invention is constructed such that a pulse-like voltage generating means supplies a pulse-like voltage across a pair of electrodes of the rare gas discharge fluorescent lamp wherein an energization time of the pulse-like voltage is equal to a half period of a wave form applied from the power source and the idle time is integral-number times as long as the half period of the wave form applied from the power source, the probability that molecules of the enclosed gas may be excited at such an energy level that they may emit much resonant ultraviolet rays of the rare gas which contributes to emission of light can be increased, so that the optical output and efficiency of the lamp are improved. Other objects and features of the invention will be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings. Figs. 1 to 5 are drawings corresponding to a rare gas discharge fluorescent lamp device according to a first embodiment of the present invention; Fig. 1 is a block diagram showing the rare gas discharge fluorescent lamp device according to this embodiment; Fig. 2 shows a relationship between ac wave form and output of the applied voltage; Fig. 3 is a characteristic view showing a relationship between the enclosed gas pressure and lamp efficiency in this embodiment; Fig. 4 is a characteristic view showing a relationship between idle period and lamp efficiency; Fig. 5 is a characteristic view showing a relationship between ac frequency and lamp efficiency; and Fig. 6 is a block diagram showing a rare gas discharge fluorescent lamp according to a second embodiment. Figs. 7 to 12 are drawings corresponding to a rare gas discharge fluorescent lamp device according to further embodiment of the present invention. Fig. 7 is a block diagram showing the rare gas discharge fluorescent lamp device according to this embodiment; Fig. 8 shows a relationship between ac wave form and output of the applied voltage; Fig. 9 is a characteristic view showing a relationship between the enclosed gas pressure and lamp efficiency in this embodiment; Fig. 10 is a characteristic view showing the relationship between idle period and lamp efficiency in this embodiment; Fig. 11 is a characteristic view showing the relationship between ac frequency and lamp efficiency; Fig. 12 is a block diagram showing a rare gas discharge fluorescent lamp according to further embodiment of the present invention; Fig. 13 is an entire constructional view of the rare gas discharge fluorescent lamp according to a conventionally known embodiment; and Fig. 14 is a vertical sectional view of the rare gas discharge fluorescent lamp device according to a conventionally known embodiment. In the following, rare gas discharge fluorescent lamp devices according to embodiments of the present invention are described with reference to the drawings. Fig. 1 indicates a block diagram showing an embodiment according to the present invention. In the figure, reference numeral 1 is a glass bulb which has a fluorescent layer 2 formed on an inner surface thereof, and rare gas X is enclosed therein. Reference numerals 3a, 3b denote electrodes respectively disposed at opposite ends of the bulb, which electrodes composing a rare gas discharge fluorescent lamp 8 (hereinafter referred to as a lamp) together with the above bulb 1. Reference numeral 18 denotes a current limiting element, one end of which is connected to the electrode 3a, and it can be a condenser, if not an inductance as used in this embodiment. Reference numeral 19 denotes a high frequency power source, and is connected to the current limiting element 18 and to the other electrode 3b of the lamp 8. Numerals 20a and 20b are both diodes, and 14 denotes a switching element, wherein the diode 20a is serially connected to the switching element 14, and this circuit is connected to the lamp 8 in parallel, as is so connected the diode 20b whose polarity is opposite to that of the diode 20a. Reference numeral 15 denotes a control means for controlling the open and closed states of the above switching element 14 by feeding pulse signals to a control electrode (base electrode) of the switching element 14. The control means 15 controls the switching element 14 to set the open state thereof to a half period of the wave form of the high frequency power source 19, and the closed state thereof to odd-number times as long as the half period, by synchronizing with the high frequency power source 19. The above switching element 14, the control means 15, the current limiting element 18, and diodes 20a and 20b compose an electric voltage generating means altogether. An operation of the rare gas discharge fluorescent lamp device as constructed above is explained below. Fig. 2 indicates a relationship among the high-frequency power source 19, the control means 15, and an output of the voltage applied to the lamp, wherein the closed state of the switching element is three times as long as the half period of the wave form of the power source. First of all, since the diode 20b is connected to the lamp 8 in parallel, the wave form from the power source is basically a rectified half wave. Then, the control means 15, synchronizing with the frequency of the high frequency power source 19, applies pulse signals to the switching element 14 to control the open and closed states thereof such that off state of the pulse signal is half to a period of the wave form from the power source, and the on state is odd-number times as long as the half period. In the case that the switching element 14 is closed by a pulse signal, since this circuit becomes equivalent to the one in which two diodes 20a, 20b, whose polarities are respectively opposite to each other, are connected to the lamp 8 in parallel, the electric current flows into the diodes, and the voltage is not applied to the lamp 8. On the other hand, when the switching element 14 is opened, an electric current does not flow into the diode 20b in the case that an electric voltage is applied thereto in the opposite direction, so that the voltage is applied to the lamp 8. However, since the open state is only for half period of the current applied from the power source, the voltage applied to the lamp is only for this half-period. Repetition of the open and closed states of the switching element 14 generates a pulse-like voltage such that an energization time is equal to a half period of the wave form from the power source, and an idle time is odd-number times as long as the half period of the wave form from the power source, and during the energization time, a glow discharge takes place between a pair of electrodes 3a and 3b, and this glow discharge excites rare gas X enclosed in the bulb 1 so that the rare gas emits peculiar ultraviolet rays therefrom. The ultraviolet rays excite the fluorescent layer 2 formed on the inner face of the bulb 1, and consequently visible rays of light are emitted and discharged to the outside of the bulb 1. A relationship between the lighting condition and characteristic of the lamp concerning the rare gas discharge fluorescent lamp constructed as above is examined. Fig. 3 shows a relationship between an enclosed rare gas pressure and a lamp efficiency. The lamp used has an outer diameter of 10 mm and an axial length of 300 mm and the gas enclosed therein is xenon gas and frequency is 50 KHz, and power of the lamp is constant at 5 W. In Fig. 3, a solid curve line indicates the occasion that the idle time is three times as long as the half period of the wave form applied from the power current of the case of Fig. 2, and a broken line indicates the case of high frequency lighting based on an ordinary ac sine wave. It can be seen from Fig. 3 that the lamp device of the embodiment of the present invention shown in Fig. 2 presents an effect of improvement in lamp efficiency and such effect of improvement in lamp efficiency depending upon a pressure of enclosed gas. Also, it can be seen from Fig. 3 that a maximum efficiency is obtained where the enclosed xenon gas pressure is within a region of several tens Torr and that the significant effect of improvement in efficiency by the present invention as compared with that in ordinary high frequency lighting can be obtained within a range of the enclosed xenon gas pressure between 10 Torr to 200 Torr. Such improvement in lamp efficiency arises from the fact that pulse-like discharge where in an energization time and an idle time alternatively appear modulates electron energy of a positive column to a high degree to increase the energy to excite the xenon gas so as to increase ultraviolet rays to be generated from the xenon gas, and also from emission of after glow light during such idle time. For example, the value of 10 Torr at which the lamp efficiency presents significant improvement corresponds to a pressure at which emission of after glow light during such idle time, which hardly appears at several Torr, appears significantly. By the way, the improvement in efficiency is comparatively low at a high pressure, but this phenomenon arises from the fact that, if the pressure is excessively high, then the electron energy is restrained by frequent collisions of electrons with xenon gas, and consequently, the electron energy is not modulated readily by pulses. Fig. 4 shows variation of the lamp efficiency in accordance with the variation of the idle time at the fixed electric frequency at 50 KHz. The lamp used here is same as that of Fig. 3 with 30 Torr pressure of the gas enclosed therein, and the lamp power is fixed to 5 W. From Fig. 4, it can be seen that lamp efficiency can be improved if the lamp is lit in such a condition that idle time thereof is longer than a half to a period of the ac frequency. Fig. 5 shows variation of lamp efficiency in accordance with the variation of the ac frequency at the fixed idle time which is three times as long as a half period of the ac wave form. The lamp used here is same as that of Fig. 3 with 30 Torr pressure of the gas enclosed therein, and the lamp power is fixed at 5 W. The solid curve line indicates the case of the embodiment shown in Fig. 1, and a broken line indicates the case of high frequency lighting based on an ordinary ac sine wave. From Fig. 5, it can be seen that a high efficiency is obtained at a frequency higher than 3 KHz with the rare gas discharge fluorescent lamp device of the embodiment of the present invention shown in Fig. 1 as compared with that in ordinary high frequency lighting. It can also be seen that, if the frequency rises to about 200 KHz, the efficiencies in the two cases present substantially same levels. Accordingly, the frequency should be higher than 3 KHz but lower than 200 KHz. It is to be noted that the reason why the efficiency drops at high frequency and becomes substantially equal to that in the case of ordinary high frequency lighting is that a plasma parameter of a positive column cannot follow such high frequency and gradually approaches a fixed condition similar to a dc current. As above, since the rare gas discharge fluorescent lamp device constructed as shown in Fig. 1 applies pulse-like voltage having idle time to the lamp, brightness and lighting efficiency of the lamp can be greatly improved. By the way, although xenon gas is enclosed in the above embodiment, rare gas other than xenon gas can be enclosed either individually or together with xenon gas to gain the same improvement in efficiency as above. Further, although a lamp having outer diameter of 10 mm is adopted in the above embodiment, various other lamps having other diameters within the range of 8 to 15.5 mm were also examined and same high efficiency was obtained as the result. Fig. 6 is a block diagram indicating another embodiment of the present invention, wherein a lamp of a hot cathode electrode type is shown. In the figure, reference numeral 1 is a glass bulb which has a fluorescent layer 2 formed on an inner surface thereof, and rare gas X is enclosed therein. Reference numeral 3a denotes an anode provided at one end of the bulb, and 3b denotes a cathode filament at the other end of the bulb, the both electrodes composing a rare gas discharge fluorescent lamp 8 (hereinafter referred to as a lamp) together with the above bulb 1. Reference numeral 18 denotes a current limiting element connected to the anode 3a, and it can be a condenser, if not an inductance as used in this embodiment. Reference numeral 19 denotes a high frequency power source, and is connected to the current limiting element 18 and to one end of the cathode filament 3b of the rare gas discharge fluorescent lamp 8. Numerals 20a and 20b are both diodes and 14 denotes a switching element, wherein the diode 20b is connected to the anode 3a and also to the other end of the cathode filament 3b having its cathode side heading for the anode side of the lamp, whereas the diode 20a is serially connected to the switching element 14, and this circuit is connected to the anode 3a and to the other end of the cathode filament 3b of the lamp 8 in parallel, as is so connected the diode 20b whose polarities opposite to that of the diode 20a. Reference numeral 15 denotes a control means for controlling the open and closed states of the above switching element 14 by feeding pulse signals to a control electrode (base electrode) of the switching element 14. The control means 15 controls the switching element 14 to set the open state thereof to a half period of the wave form of the high frequency power source 19, and the closed state thereof to odd-number times as long as the half period, by synchronizing with the high frequency power source 19. The rare gas discharge fluorescent lamp device of hot cathode type as constructed above could also obtain same improvement in efficiency as the case of Fig. 1. Further, in the case of the embodiment as shown in Fig. 6, the electric current flows into the diode through the filament of the cathode side of the lamp during the idle time of the applied voltage, and preheating function is thus also provided. Accordingly, the above embodiment of Fig. 6 can improve brightness and lighting efficiency of the lamp, and obviates any additional circuit to preheat the electrode, thereby making it possible to simplify the circuit as a whole. In the following, rare gas discharge fluorescent lamp devices according to further embodiments of the present invention are described with reference to the drawings. Fig. 7 is a block diagram showing further embodiment according to the present invention. In the figure, reference numeral 1 is a glass bulb which has a fluorescent layer 2 formed on an inner surface thereof, and rare gas X is enclosed therein. Reference numerals 3a and 3b denote electrodes respectively disposed at opposite ends of the bulb 1, which electrodes composing a rare gas discharge fluorescent lamp 8 (hereinafter referred to as a lamp) together with the above bulb 1. Reference numeral 18 denotes a current limiting element, one end of which is connected to the electrode 3c, and it can be a condenser, if not an inductance as used in this embodiment. Reference numeral 19 denotes a high frequency power source, and is connected to the current limiting element 18 and to the other electrode 3d of the lamp 8. Numerals 21a and 21b are both diodes, and 14a, 14b are switching elements, wherein the diodes 21a and 21b are serially connected respectively to the switching elements 14a and 14b, with their polarities in the opposite directions from each other, and also connected to the lamp 8 respectively in parallel. Reference numerals 15a and 15b denote control means for respectively controlling the open and closed states of the above switching elements 14a and 14b by feeding pulse signals to a control electrode (base electrode) of the respective switching elements. The control means 15a, 15b control respectively the switching elements 14a, 14b to set the open states thereof to a half period of the wave form of the high frequency power source 19, and the closed states thereof to integral-number times as long as the half period, by synchronizing with the high frequency power source 19. The above switching elements, 14a, 14b, the control means 15a, 15b, the current limiting element 18, diodes 21a, 21b compose an electric voltage generating means altogether. An operation of the rare gas discharge fluorescent lamp levice as constructed above is explained below. Fig. 8 indicates a relationship among the high-frequency power source 19, the control means 15a, 15b, and an output of the voltage applied to the lamp, wherein the closed state of the switching element is twice as long as the half period of the wave form of the power source. First of all, since the control means 15a, 15b, synchronizing with the frequency of the high frequency power source 19, applies pulse signals respectively to the switching elements 14a, 14b to control the open and closed states thereof such that the off state of the pulse signal is half to a period of the wave form from the power source, and the on state is integral-number times as long as the half period. In the case that the switching elements 14a, 14b are closed by pulse signals, since this circuit becomes equivalent to the state in which two diodes 21a, 21b, whose polarities are respectively opposite to each other, are connected to the lamp 8 in parallel, the electric current flows into the diodes, and the voltage is not applied to the lamp 8. On the other hand, when the switching elements 14a, 14b are in the open state, an electric current does not flow into the diodes 21a, 21b, so that the voltage is applied to the lamp 8. However, since the open state is only for half period of the current applied from the power source, the voltage applied to the lamp is only for this half period, and in addition, the polarities thereof are alternatively changing. Repetition of the open and closed states of the switching elements generates a pulse-like voltage alternatively changing its polarity such that an energization time is equal to a half of the wave form from the power source and the idle time is integral-number times as long as the half period of the wave form from the power source, and during the energization time, a glow discharge takes place between a pair of electrodes 3c and 3d, and this glow discharge excites rare gas X enclosed in the bulb 1 so that the rare gas emits peculiar ultraviolet rays therefrom. The ultraviolet rays excite the fluorescent layer 2 formed on the inner face of the bulb 1, and consequently visible rays of light are emitted and discharged to the outside of the bulb 1. A relationship between the lighting condition and characteristic of the lamp concerning the rare gas discharge fluorescent lamp constructed as above is examined. Fig. 9 shows a relationship between an enclosed gas pressure and a lamp efficiency. The lamp used here has an outer diameter of 10 mm and an axial length of 300 mm and the gas enclosed therein is xenon gas and frequency is 50 KHz, and power of the lamp is constant at 5 W. In Fig. 9 a solid curve line indicates the occasion that the idle time is four times as long as the case of Fig. 7, and a broken line indicates the case of high frequency lighting based on an ordinary ac sine wave. It can be seen from Fig. 9 that the lamp device of the embodiment of the present invention shown in Fig. 7 presents an effect of improvement in lamp efficiency and such effect of improvement in lamp efficiency depending upon a pressure of enclosed gas. Also, it can be seen from Fig. 9 that a maximum efficiency is obtained where the enclosed xenon gas pressure is within a region of several tens Torr and that the significant effect of improvement in efficiency by the present invention as compared with that in ordinary high frequency lighting can be obtained within a range of the enclosed xenon gas pressure between 10 Torr to 200 Torr. Such improvement in lamp efficiency arises from the fact that pulse-like discharge wherein an energization time and an idle time alternatively appear modulates electron energy of a positive column to a high degree to increase the energy to excite the xenon gas so as to increase ultraviolet rays to be generated from the xenon gas, and also from emission of after glow light during such idle time. For example, the value of 10 Torr at which the lamp efficiency presents significant improvement corresponds to a pressure at which emission of after glow light during such idle time, which hardly appears at several Torr, appears significantly. By the way, the improvement in efficiency is comparatively low at a high pressure, but this phenomenon arises from the fact that, if the pressure is excessively high, then the electron energy is restrained by frequent collisions of electrons with xenon gas, and consequently, the electron energy is not modulated readily by pulses. Fig. 10 shows variation of the lamp efficiency in accordance with the variation of the idle time at the fixed electric frequency at 50 KHz. The lamp used here is same as that of Fig. 9 with 30 Torr pressure of the gas enclosed therein, and the lamp power is fixed to 5 W. From Fig. 10, it can be seen that lamp efficiency can be improved if the lamp is lit in such a condition that idle time thereof is longer than a half to a period of the ac frequency. Fig. 11 shows variation of lamp efficiency in accordance with the variation of the ac frequency at the fixed idle time which is twice as long as a half period of the ac wave form. The lamp used here is same as that of Fig. 9 with 30 Torr pressure of the gas enclosed therein, and the lamp power is fixed at 5 W. The solid curve line indicates the case of the embodiment shown in Fig. 7, and a broken line indicates the case of high frequency lighting based on an ordinary ac sine wave. From Fig. 11, it can be seen that a high efficiency is obtained at a frequency higher than 3 KHz with the rare gas discharge fluorescent lamp device of the embodiment of the present invention shown in Fig. 7 as compared with that in ordinary high frequency lighting. It can also be seen that, if the frequency rises to about 200 KHz, the efficiencies in the two cases present substantially same levels. Accordingly, the frequency should be higher than 3 KHz but lower than 200 KHz. It is to be noted that the reason why the efficiency drops at high frequency and becomes substantially equal to that in the case of ordinary high frequency lighting is that a plasma parameter of a positive column cannot follow such high frequency and gradually approaches a fixed condition similar to a dc current. As above, since the rare gas discharge fluorescent lamp device constructed as shown in Fig. 7 applies pulse-like voltage having idle time to the lamp, brightness and lighting efficiency of the lamp can be greatly improved. By the way, although xenon gas is enclosed in the above embodiment, rare gas other than xenon gas can be enclosed either individually or together with xenon gas to gain the same improvement in efficiency as above. Further, although a lamp having outer diameter of 10 mm is adopted in the above embodiment, various other lamps having other diameters within the range of 8 to 15.5 mm were also examined and same high efficiency was obtained as the result. A rare gas discharge fluorescent lamp according to further embodiment of the present invention is shown in Fig. 12. In the figure, reference numeral 1 is a glass bulb which has a fluorescent layer 2 formed on an inner surface thereof, and rare gas X is enclosed therein. Reference numerals 3e and 3f denote filament electrodes respectively disposed at opposite ends of the bulb, which electrodes composing a rare gas discharge fluorescent lamp 8 together with the above bulb 1. Reference numeral 18 denotes a current limiting element, one end of which is connected to one end of a cathode filament 3e, and it can be a condenser, if not an inductance as used in this embodiment. Reference numeral 19 denotes a high frequency power source, and is connected to the current limiting element 18 and to the other electrode 3f of the lamp 8. Reference numerals 21a and 21b are both diodes, and 14a, 14b are switching elements, wherein the diodes 21a and 21b are serially connected respectively to the switching elements 14a and 14b, with their polarities contrary to each other, and also connected to the other end of the filament 3e of the lamp 8 respectively in parallel. Reference numerals 15a, 15b are control means for respectively controlling the open and closed states of the above switching elements 14a, 14b by feeding pulse signals to a control electrode (base electrode) of the respective switching elements. The control means 15a, 15b control respectively the switching elements to set the open states thereof to a half wave to a half period of the wave form of the high frequency power source 19, and the closed state thereof to integral-number times as long as the half period, by synchronizing with the high frequency power source 19. The rare gas discharge fluorescent lamp device as constructed above could also obtain the same improvement in efficiency in brightness as the case of the embodiment shown in Fig. 7. furhter, in the case of the embodiment shown in Fig. 12, the electric current flows into the diode through the filament of the cathode of the lamp during the idle time of the applied voltage, and preheating function is also provided. Accordingly, the above embodiment of Fig. 12 can improve brightness and lighting efficiency of the lamp, and obviates any additional circuit to preheat the electrode, thereby making it possible to simplify the circuit as a whole. Thus, a rare gas discharge lamp device according to an embodiment of the present invention is constructed such that it comprises a rare gas discharge fluorescent lamp wherein rare gas is enclosed in the inside of a glass bulb which has a fluorescent layer formed on an inner face thereof and has a pair of electrodes at the opposite ends thereof, a high frequency power source for supplying frequency higher than 3 KHz but lower than 200 KHz, and an electric voltage generating means for applying pulse-like voltage across a pair of electrodes of the rare gas discharge fluorescent lamp, the pulse-like voltage having a period divided into an energization time and an idle time, wherein the energization time is equal to a half period of a wave form applied from said power source and the idle time is odd-number times as long as the half period of the wave form applied from the power source, whereby a rare gas discharge fluorescent lamp having high efficiency in brightness and lighting effect is made possible. And further, a rare gas discharge lamp device according to a further embodiment is constructed such that it comprises rare gas discharge fluorescent lamp wherein rare gas is enclosed in the inside of a glass bulb which has a fluorescent layer formed on an inner face thereof and has a pair of electrodes at the opposite ends thereof, a high frequency power source for supplying frequency higher than 3 KHz but lower than 200 KHz, and an electric voltage generating means for applying pulse-like voltage across a pair of electrodes of the rare gas discharge fluorescent lamp by alternatively changing respective polarities, the pulse-like voltage having a period divided into an energization time and an idle time, wherein the energization time is equal to a half period of a wave form applied from the power source and the idle time is integral-number times as long as the half period of the wave form applied from the power source, whereby a rare gas discharge fluorescent lamp having high efficiency in brightness and lighting effect is made possible.

Claims: A rare gas discharge fluorescent lamp device comprising: a rare gas discharge fluorescent lamp (8), wherein rare gas is enclosed in the inside of a glass bulb (1), which has a fluorescent layer (2) formed on an inner face thereof and has a pair of electrodes (3a, 3b) at the opposite ends thereof, characterized by high frequency power source (19) for supplying frequency higher than 3 kHz but lower than 200 kHz; and an electric voltage generating means (14, 15, 20a; 14a, 15a, 21a, 14b, 15b, 21b) for applying pulse-like voltage across said pair of electrodes (3a, 3b) of said rare gas discharge fluorescent lamp (8), said pulse-like voltage having a period divided into an energization time and an idle time, wherein said energization time is equal to one half peroid of a wave form applied from said power source (19) and said idle time corresponds to an at least odd integral number of times said half period of said wave form applied from said power source (19). A rare gas discharge fluorescent lamp device as claimed in claim 1, characterized in that said electric voltage generating means (14a, 15a, 21a, 14b, 15b, 21b) apply said pulse-like voltage across said pair of electrodes (3a, 3b) of said rare gas discharge fluorescent lamp (8) by alternatively changing respective polarities and in that said idle time corresponds to an integral number of times said half period of the wave form applied from said power source (19). A rare gas discharge fluorescent lamp device as claimed in claim 1, characterized in that said electric voltage generating means (14, 15, 20a, 20b) comprises a switching element (14), control means (15) for controlling said switching element, and two diodes (20a, 20b) whose polarities are contrary to each other, and respectively connected to said rare gas discharge fluorescent lamp (8) in parallel, wherein one of said two diodes is serially connected to said switching element (14). A rare gas discharge fluorescent lamp device claimed in claim 1, wherein the cathode (3b) of said rare gas discharge fluorescent lamp (8) is a hot cathode filament. A rare gas discharge fluorescent lamp device as claimed in claim 2, characterized in that said electric voltage generating means (14a, 15a, 14b, 15b, 21a, 21b) comprises two switching elements (14a, 14b) two control means (15c, 15b) for respectively controlling said two switching elements, and two diodes (21a, 21b) whose polarities are contrary to each other and respectively connected to said rare gas discharge fluorescent lamp (8) in parallel, and wherein said two diodes (21a, 21b) are serially connected to said two respective switching elements (14, 14b). A rare gas discharge fluorescent lamp device as claimed in claim 2, wherein the pair of electrodes of said rare gas discharge fluorescent lamp (8) are both made of filament.

Inventors: KARINO MASAO, MATSUMOTO SADAYUKI, SAIKATSU TAKEO, SAKURAI TAKEHIKO, YAMAZAKI HIROYOSHI, KARINO, MASAO, MATSUMOTO, SADAYUKI, SAIKATSU, TAKEO, SAKURAI, TAKEHIKO, YAMAZAKI, HIROYOSHI, Karino, Masao, c/o Mitsubishi Denki K.K., MATSUMOTO, SADAYUKI, C/O MITSUBISHI DENKI K.K., SAIKATSU, TAKEO, C/O MITSUBISHI DENKI K.K., SAKURAI, TAKEHIKO, C/O MITSUBISHI DENKI K.K., YAMAZAKI, HIROYOSHI, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1991
Main classification: H05B41
IPC codes: H05B41, H01J61