GB2206992A

GB2206992A - Single-ended discharge lamp

Info

Publication number: GB2206992A
Application number: GB08813736A
Authority: GB
Inventors: Kazuo Honda; Atsushi Matsuura; Shinji Inukai; Yasuhiro Iwafuji; Hisanori Sano
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1987-06-11
Filing date: 1988-06-10
Publication date: 1989-01-18
Anticipated expiration: 2008-06-10
Also published as: CA1305996C; FR2616588A1; AU1752488A; GB2206992B; GB8813736D0; AU604126B2

Abstract

A high intensity discharge lamp (20) includes a pair of electrodes (31, 32) sealed into the same end of the envelope (21), and an arrangement for adjusting the temperature at the wall of the envelope (21) adjacent to the arc supporting electrode rods (33, 34), to minimize the differences in the wall temperature under different orientations of the lamp (20), whereby the luminous efficiency of the lamp (20) is substantially independent of its orientation. As shown in Fig. 2 this may be achieved by providing a groove 81 in the envelope between the electrodes 33,34 such that the ratio L1/L2 of the distances from the arc centreline (i) to the bottom of the groove and (ii) to the envelope adjacent the groove is L1/L2</=1.3. Alternatively, Fig.6, insulating films 24,25 may be provided on the envelope behind the electrodes, the films having a conical angle of 10 DEG -30 DEG . <IMAGE>

Description

"HIGH INTENSITY DISCHARGE LAMP OF THE ONE SIDE SEALED TYPE CAPABLE OF COMPENSATING FOR THE CHANGE OF LUMINOUS EFFICIENCY CAUSED BY ITS DIFFERENT LIGHTING ANGLES AND MANUFACTURING METHOD OF THE SAME" The present invention relates to a high intensity discharge lamp and a method of manufacturing the same.

More particularly, it relates to a metal halide lamp and a method of manufacturing the same.

The high intensity discharge lamp was conventionally used for outdoor or factory illumination but it has been used these days for illuminating the inside of structures such as the stores whose ceilings are low.

There can be often seen these cases where particularly the metal halide lamp is made smaller in size and attached to the low ceiling to use it as an illuminating light source because it has high luminous efficiency and color display.

One thing which has to be done to make the metal halide lame smaller in size is that the lamp used is made to consume a smaller amount of power. Another thing is that the lamp is made to have as smaller a number of component parts as possible and these parts are made as smaller in size as possible.

The second measure has been mainly studied and the development of a metal halide lamp with its one side sealed, for example, of a quartz double-bulb type, has been advanced instead of the lamp of the conventional both-side sealed type. The lamp of the both-side sealed type has two sealed portions while the one of the one side sealed type has one sealed portion. In the case of a metal halide lamp of the quartz double-bulb type with a luminous bulb and an outer bulb. Each bulb has only one sealed portion and.this therefore enables the whole of the lamp to be made smaller in size.The advantage of the luminous bulb having only one sealed portion resides in that surface area becomes substantially smaller and heat loss is thus made less, as compared with the one of the conventional both-side sealed type, because the sealed portion which is a main cause of the heat loss is present only at one side of the lamp.

Further, the process of sealing the lamp can be made simpler because the sealed portion is only at one side.

However, because this luminous bulb of the one side sealed type is provided with a pair of main electrodes arranged at only one small sealed portion, the distance between front ends of these main electrodes is relatively small and limited to a predetermined length. In other words, this kind of luminous bulb has a larger volume behind their main electrodes compaired with the volume between the front ends of the main electrodes.

More specifically, the ratio of volume VAl located between the front ends of the main electrodes relative to volume VB1 defined by the remaining volume in the luminous bulb, that is, VA1/VB1, is smaller than 1.5.

Under this conditions, the temperature of the coldest portion in the luminous bulb is likely to change greatly when its lighting angle is changed because the coldest portion can be shifted because of the bending of an arc which is formed between the main electrodes.

Therefore, luminous color and.efficiency can be changed greatly when a lamp changes lighting positions, limiting the extent of practical use of lamps.

An object of the present invention is therefore to provide a metal halide lamp of the one side sealed type having the least property changes for its changing lighting angles.

Another object of the present invention is to provide a method of manufacturing the metal halide lamp of the one side sealed type having the least property changes for its changing lighting angles.

A further object of the present invention is to provide a metal halide lamp of the one side sealed type with less irregularity of lamp property for its changing lighting angles.

A still further object of the present invention is to provide a method of manufacturing the metal halide lamp of the one side sealed type with less irregularity of lamp property for its changing lighting angles.

The present invention provides a high intensity discharge lamp comprising an envelope formed of vitreous high temperature resistant material, a pair of electrodes each having a metal rod and an arc supporting electrode, each of the metal rods being sealed at one end of the envelope, and means for adjusting the temperature at the wall of the envelope adjacent to the arc supporting rods, to minimize the differences in the wall temperature under different lighting postures of the lamp, whereby the luminous efficiency of the lamp is substantially independent of the lighting postures of the lamp.

This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 shows the metal halide lamp to which a luminous bulb of the present invention is applied; Fig. 2 is a vertically-sectioned view showing an example of the luminous bulb according to the present invention; Fig. 3 is a vertically-sectioned view showing the luminous bulb of Fig. 2 as it is turned round the vertical axis at an angle of 90 ; Fig. 4 is a graph showing the relation between lighting angles (e0) of the lamp and luminous efficiencies (relative values); Fig. 5 shows the curves of an arc, caused by changing lighting angles of the lamp; and Fig. 6 shows another example of the luminous bulb according to the present invention.

An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

Fig. 1 shows a construction of the metal halide lamp to which a luminous bulb of the present invention is applied. The metal halide lamp shown in Fig. 1 includes outer bulb 11, luminous bulb 20 housed in outer bulb 11, and sealing sections 12 and 22 of these two bulbs. Outer bulb 11 is made of quartz glass and has the sealing section located on only one side thereof.

This outer bulb 11 is therefore of the one side sealed type. A base (not shown) is usually attached to sealing section 12. Luminous bulb 20 includes bulb body (envelope) 21, main electrodes 31 and 32, sealing section 22, metal foils 41 and 42, and lead lines 51 and 52. Luminous bulb 20 is also of the one side sealed type, and sealing section 22 is formed on only one side of bulb body (envelope) 21. The volume of bulb body (envelope) 21 is 0.5 cc. A pair of main electrodes 31 and 32 each of which is made of thoriated tungsten, for example, and has a diameter of 0.5 mm, are arranged inside the bulb body (envelope) 21. Base ends (metal rods) 37 and 38 of main electrodes 31 and 32 are connected to metal foils 41 and 42 respectively embedded in sealing section 22. One end of each of lead lines 51 and 52 are also connected to these metal foils 41 and 42 respectively. The other end of each of luminous bulb lead lines 51 and 52 are respectively connected to metal foils 61 and 62 air-tightly embedded in sealing section 12 of outer bulb 11. Further, outer bulb lead lines 71 and 72 are connected to these metal foils 61 and 62.

Mercury 26 and argon gas which serve as the starting gas are sealed in bulb body (envelope) 21, and scandium iodide and sodium iodide which serve as the metal halide are further sealed therein at a ratio of 1 : 5. When bulb body (envelope) 21 is sealed, mercury 26 is attached in the form of liquid spheres on the inner wall thereof.

In the case of the metal halide lamp, a voltage is applied to the paired main electrodes, and a discharge is generated in the mercury vapor between the paired electrodes to emit light. The intensity of this light increases as the vapor pressure of the sealed mercury increases. It is also well known that the vapor pressure of mercury is determined by the bulb wall temperature in the bulb body (envelope) 21. It can therefore be said that the intensity of the lamp is determined by the bulb wall temperature.

Fig. 5 shdws that an arc generated between arc supporting electrodes 33 and 34 of paired electrodes 31 and 32 curves differently depending upon the different lighting angles of the lamp. As is apparent from Fig. 5, the arc is curves differently depending upon the position of the lit lamp. The distance extending from the center of the arc, which is the highest in temperature, to the farthest bulb inner wall of the lamp, which is the coldest portion, thus changes depending upon the position of the lit lamp, and the temperature at the coldest portion of the lamp changes accordingly depending upon the position of the lit lamp.

This changing. ratio becomes large particularly when VA1/VB1 S 1.5.

Fig. 2 shows an example of the present invention.

In Fig. 2, volume VA (or hatched portion) in bulb body (envelope) 21, located between arc supporting electrodes 33 and 34 of paired main electrodes 31 and 32 is about 0.36cc and volume vB, the remaining volume in bulb body (envelope) 21 is about 0.14 cc. Therefore, VA/VB = 0.36/0.14 . 2.5. As shown in Figs. 2 and 3, inner wall face 23 of bulb body (envelope) 21 appears to be elliptically (Fig. 2) or circularly shaped, (Fig. 3) depending upon the angle at which bulb body (envelope) 21 is viewed. Further, groove 81 is formed at a part of inner wall face 23 of bulb body (envelope) 21. This groove 81 is created when bulb body (envelope) 21 is crush sealed.It is assumed that the distance extending from line A which extends between arc supporting electrodes 33 and 34 of main electrodes 31 and 32 to inner wall face 23 of bulb body (envelope) 21 be L2 and that the distance extending from line A to the deepest of groove 81 be L1. It is set in this case that L1/L2 -. 1.1.

When the lamp has this arrangement, it is obvious that remaining volume VB is smaller than the conventional one. Therefore, the distance extending from the arc generating area where arc discharge is carried out when the lamp is turned on to inner wall face 23 of bulb body (envelope) 21 can be made shorter. The temperature at the coldest portion of the inner wall of bulb body (envelope) 21 can be thus raised and it is also made possible to keep the temperature change least for its changing lighting angles. According to experimental'data, the relative value of luminous efficiency at the time when the lit lamp was set horizontal (the arc becomes vertical) was about 95, providing that the luminous efficiency was 100 at the time when the lit lamp was set vertical (the arc becomes horizontal).

This means the changing ratio was just about 5%.

Fig. 4 is a graph showing the relation between lighting angles or postures (8") of the lamp and luminous efficiencies (relative values) thereof. It can be understood from Fig. 4 that the relation between lighting angles and luminous efficiencies of the lamp changes as the rate of VA and VB changes. The lighting angle of 8 = 0 represents vertical lighting (the arc is horizontal) and the lighting angle of 8 = 90" represents horizontal lighting (the arc is vertical). As apparent from Fig. 4, the change of luminous efficiency becomes larger as the angle 0 becomes larger from 0 to 90" for each value of the VA/VB. This is because the arc does not become linear but curved depending upon the lighting angle of the lamp, as described above.Further, this change of luminous efficiency differs greatly depending upon the rate of VA/VB. Providing that the permissible change rate for practical lamp use is 20% at maximum, Fig. 4 shows that the value of VA/VB should be between 1.5 and 5.0, that is, 1.5 < VA/VB < 5.0. More preferably, when the rate is in the range of 2.0 < VA/VB < 4.0, the changing ratio of luminous efficiency can be made smaller than 10%. When the changing ratio of luminous efficiency is made small, the changing ratio of other lamp properties such as color change can be made small.

The reason why the change of luminous efficiency becomes larger as the rate of VA and VB becomes smaller for its changing lighting postures is supposed that remaining volume VB becomes larger and temperature irregularity at the coldest portion of inner wall 23 of bulb body (envelope) 21 is made larger by the change of the lighting posture. On the other hand, the reason why the changing ratio of luminous efficiency becomes larger as the rate of VA and VB becomes larger for its changing lighting postures is supposed that the distance between arc supporting electrodes 33 and 34 of main electrodes 31 and 32 becomes longer and the curve of the arc is thus made more prominent to thereby increase heat loss.

Under mass production of the lamps, there produced those inferior lamps which satisfied the condition of 1.5 < VA/VB S 5.0 but whose efficiency for its different lighting angles changed more than 20%. As the result of comparing these inferior lamps with those good ones in which VA/VB is less than 10%, it has been found that the depth of groove 81 formed on inner wall face 23 of bulb body (envelope) 21 at the time of manufacture is deeper for those lamps whose luminous efficiency changes more than 20%. The method of manufacturing luminous bulb 20 includes a process of heating and melting the opening portion of a dome-like product which is made of quartz glass and then crush-sealing the opening portion by means of a pair of jigs to form a sealing section.

Groove 81 is unavoidably formed along the inner end of the sealing section when this sealing section is formed.

The depth of groove 81 differs depending upon the lamps manufactured. In order to define the depth of groove 81, it is assumed that the distance extending from line A between arc supporting electrodes 33 and 34 of main electrodes 31 and 32 to inner wall face 23 of bulb body (envelope) 21 be L2 and that the distance extending from line A to the deepest of groove 81 be L1. Therefore, the depth of groove 81 can be defined as the difference of these two distances or L1 - L2. Further, the rate of these two distances L1 and L2 is considered. The lighting direction property of the lamps were studied in detail changing values of L1 - L2 (or depth of groove 81) and L1/L2. As the result, the changing ratio of lamp efficiency which depends upon the lighting direction became larger as the depth of groove 81 or L1 - L2 was made larger.When L1/L2 met the relation of L1/L2 S 1.3, the changing ratio of lamp efficiency became smaller than 20%. This percentage is in the practically permissible range.

As described above, therefore, it is possible to keep the temperature change at the coldest portion of the inner wall face of bulb body (envelope) 21 least for changing lighting postures when the rate of volume VA in bulb body (envelope) 21 between arc supporting electrodes 33 and 34 of paired main electrodes 31 and 32 and volume VB remaining in bulb body (envelope) 21 except volume VA is limited to 1.5 < VA/VB < 5 at the time of manufacturing the lamps. It is also possible to prevent those lamps which satisfy the relation of 1.5 S VA/VB I 5 but have such a groove depth as not to satisfy the relation of L1/L2 S 1.3 from being manufactured, when the rate of the two distances relating to the depth of groove 81 is limited to L1/L2 S 1.3 at the time of manufacturing the lamps.

Even when the lamp lighting posture is changed from vertical to horizontal by 90 , changes of luminous efficiency and lamp property such as the color of light emitted can be made less than 20%. Therefore, a metal halide lamp which is smaller in size, higher in practical value and free in its posture when it is lit can be produced.

Fig. 6 is another embodiment of this invention, showing a luminous bulb 20 used in a metal halide lamp of 150 W. Bulb body (envelope) 21 is made of quartz glass and formed like a substantially elliptical sphere, having a volume of 0.5 cc. Like reference numerals in Fig. 6 designate corresponding parts in the several views.

A pair of electrodes 31 and 32 are separated from and opposed one another in bulb body (envelope) 21 in the direction of the longitudinal axis (or bulb axis) of the bulb body (envelope) 21 and they are embedded in crush-melted sealing section 22 on one side of the bulb body (envelope) 21.

Each of electrodes 31 and 32 comprises base ends (metal rods) 37 or 38 and arc supporting electrode 35 or 36 which serves to increase heat capacity, and these base ends (metal rods) 37 and 38 and coil portions 35 and 36 are made as a unit by thoriated tungsten whose diameter is 0.5 mm. Arc supporting electrodes 35 and 36 of the electrodes 31 and 32 are separated from each other by about 6.8 mm and opposed to each other in the bulb body (envelope) 21 in the direction of the bulb axis, and base ends (metal rods) 37 and 38 thereof are connected to metal foils 41 and 42 such as Mo embedded in crush-melted sealing section 22. Metal foils 41 and 42 are connected to external lead lines 51 and 52, respectively.

Insulating films 24 and 25 are formed on the outer face of this bulb body (envelope) 21 behind arc supporting electrodes 35 and 36 of the electrodes 31 and 32. These insulating films 24 and 25 are made of At203, TiO2, SiO2 or the like and coated on the outer face of the bulb body (envelope) 21 behind coil portions 35 and 36 of the electrodes 31 and 32.

The areas on the bulb body (envelope) 21 where insulating films 24 and 25 are coated are formed in a conical angle 8 of 10 - 30 whose apex is the center 0 of bulb body (envelope) 21, and arc supporting electrodes 35 and 36 of the electrodes 31 and 32 are naturally in the areas of this conical angle 8.

The luminous bulb 20 having the above-described arrangement is housed in the outer bulb 11 shown in Fig. 1 of the one side sealed type made of quartz glass.

According to this embodiment of the present invention having the above-described arrangement, arc discharge between arc supporting electrodes 35 and 36 of paired electrodes 31 and 32 are created along the direction of the bulb axis while the lamp is being lit.

Sealing section 22 formed at one side of the bulb body (envelope) 21 in a direction perpendicular to the direction of the bulb axis is thus heated by radiation heat generated by the arc discharge. Therefore, the coldest portion are formed not at sealing section 22 in the discharge space but at those portions x of the bulb body (envelope) 21 which are remote from arc supporting electrodes 35 and 36 of the electrodes 31 and 32, and the temperature at these portions x lowers depending upon the posture of the lamp lit.

However, since insulating films 24 and 25 are formed on the outer face of these coldest portions x, insulating films 24 and 25 reflect the radiation heat coming from the arc discharge and electrodes 31, 32 to raise the temperature at coldest portions x and helps the metal halide which tends to gather at these coldest portions x evaporate to raise the vapor pressure in bulb body (envelope) 21, so that the luminous efficiency and the color display of the lamp can be enhanced, preventing the temperature at the coldest portions x from being lowered depending upon the posture of the lamp lit.

The areas on the bulb body (envelope) 21 where insulating films 24 and 25 are coated have a conical angle e of 10 - 30 respectively whose apex is the center 0 of bulb body (envelope) 21. This reason will be described.

The following table shows test results relating to how the luminous efficiency and the color display of the lamp changes when the areas on the bulb body (envelope) 21 whose insulating films 24 and 25 are coated are changed.

As apparent from the table, the insulating effect is enhanced as the area of the insulating films 24 and 25 coated become larger. The luminous efficiency and the color display of the lamp are thus enhanced but when the area of the insulating films 24 and 25 coated becomes too large, the amount of light emitted from the lamp is lowered because light shielding effect created by the insulating films 24 and 25 becomes high.

Table

Luminous Efficiency % Color Display Ra % Conical (Values relative to (values relative to Angle 0 lamps having no lamps having no insulating film) insulating film 5O 100 100 10 105 102 20 108 104 30 105 106 400 95 110 It is therefore needed that the areas on the bulb body (envelope) 21 where insulating films 24 and 25 are coated are in a conical angle o of 10 - 30 whose apex is center 0 of bulb body (envelope) 21.

When insulating film 24 and 25 are coated in these areas, they reflect infrared radiation to thereby heat those shoulder portions of sealing section 22 which oppose to insulating films 24 and 25, respectively.

Heat escaped through sealing section 22 can be thus supplemented to raise the temperature at that side of sealing section 22 which faces the discharge space, thereby enhancing the luminous efficiency and the color display of the lamp.

The present invention can be applied not only to the metal halide lamp which has been described above but also to any of those discharge lamps which have a bulb body of the one side sealed type. Therefore, the present invention may be applied to the metal vapor discharge lamp such as the high pressure mercury lamp.

As described above, the insulating films are formed on the outer face of the bulb body behind the electrodes and the areas on the bulb body whose the insulating films are coated are defined to be in the conical angle of 10 - 30 whose apex is the center of the bulb body.

Therefore, temperature rise at the coldest portions which may be created behind the electrodes can be accelerated to raise the vapor pressure of the luminous metal, thereby enabling the luminous efficiency and the color display of the lamp to be enhanced.

Claims

Claims:

1. A high intensity discharge lamp comprising: an envelope formed of vitreous high temperature resistant material; a pair of electrodes each having a metal rod and an arc supporting electrode, each of said metal rods being sealed at one end of said envelope; and means for adjusting the temperature at the wall of said envelope adjacent to said arc supporting rods, to minimize the differences in said wall temperature under different lighting postures of the lamp, whereby the luminous efficiency of the lamp is substantially independent of the lighting postures of the lamp.

2. The high intensity discharge lamp according to claim 1, wherein a space is defined by said envelope and said arc supporting electrodes, said space having a volume VA which is located between said arc supporting electrodes and has a specific relationship with volume VB which is the difference between VA and the volume of said envelope.

3. The high intensity discharge lamp according to claim 2, wherein said relationship is expressed as 1.5 < VA/VB < 5.0.

4. The high intensity discharge lamp according to claim 2, wherein a continuous groove is defined by a portion of said envelope located between the metal rods of said electrodes, and distance L1 between said arc supporting electrodes, on the one hand, and the bottom of said continuous groove,- on the other hand, and distance L2 which is the difference between distance L1 and the depth of said groove has a relationship of: L1/L2 < 1.3.

5. The high intensity discharge lamp according to claim 1, wherein insulating films are formed on that portion of said envelope which is located behind said electrodes.

6. The high intensity discharge lamp according to claim 5, wherein said insulating films have areas defined by a conical angle of 10 -30 the apex of which is the center of said envelope.

7. A method of manufacturing a high intensity discharge lamp, comprising the steps of: forming an envelope of vitreous high temperature resistant material; incorporating a pair of electrodes into said envelope, each of said electrodes having a metal rod and an arc supporting electrode; sealing said metal rods at one end of said envelope; and adjusting the temperature at the wall of said envelope adjacent to said arc supporting electrodes, to minimize the differences in said wall temperature under different lighting postures of the lamp, whereby the luminous efficiency for the lamp is substantially independent of the lighting postures of the lamp.

8. The method according to claim 7, wherein a space is defined by said envelope and said arc supporting electrodes, said space having a volume VA which is located between said arc supporting electrodes and has a specific relationship with volume VB which is the difference between VA and the volume of said envelope.

9. The method according to claim 8, wherein said relationship is expressed as 1.5 < VA/VB < 5.0.

10. The method according to claim 8, wherein a continuous groove is defined by a portion of said envelope located between the metal rods of said electrodes, and distance L1 between said arc supporting electrodes, on the one hand, and the bottom of said continuous groove, on the other hand, and distance L2 which is the difference between distance L1 and the depth of said groove has a relationship of: L1/L2 < 1.3.

11. The method according to claim 7, wherein insulating films are formed on that portion of said envelope which is located behind said electrodes.

12. The method according to claim 11, wherein said insulating films have areas defined by a conical angle of 10 -30 the apex of which is the center of said envelope.

13. A high intensity discharge lamp, substantially as hereinbefore described with reference to Figs. 1 to 6.

14. A manufacturing method of a high intensity discharge lamp, substantially as hereinbefore described with reference to Figs. 1 to 6.