CA1108214A - Low pressure sodium vapor discharge lamp - Google Patents
Low pressure sodium vapor discharge lampInfo
- Publication number
- CA1108214A CA1108214A CA303,069A CA303069A CA1108214A CA 1108214 A CA1108214 A CA 1108214A CA 303069 A CA303069 A CA 303069A CA 1108214 A CA1108214 A CA 1108214A
- Authority
- CA
- Canada
- Prior art keywords
- lamp
- discharge tube
- outer envelope
- low pressure
- sodium vapor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/30—Vessels; Containers
- H01J61/35—Vessels; Containers provided with coatings on the walls thereof; Selection of materials for the coatings
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/52—Cooling arrangements; Heating arrangements; Means for circulating gas or vapour within the discharge space
Abstract
LOW PRESSURE SODIUM VAPOR DISCHARGE LAMP
ABSTRACT OF THE DISCLOSURE
A low pressure sodium vapor discharge lamp for generating directional light output, the lamp including a cylindrical discharge tube within a cylindrical outer envelope.
The outer envelope is provided with a diffuse coating which is highly reflective of visible sodium light and which defines a clear aperture on the outer envelope for the directional escape of visible light.
The space between the inner discharge tube and the outer envelope is air filled to provide conductive and convective heat dissipation from the discharge tube.
Sodium condensation takes place in a plurality of spaced reservoirs located in the portion of the discharge tube away from the aperture to keep that portion of the discharge tube facing the aperture clear.
A heater coil is wound around the inner discharge tube to keep it at a desired standby temperature for lamp use on demand. The lamp filament electrodes are also maintained at standby temperature to improve the illumination profile along the lamp.
ABSTRACT OF THE DISCLOSURE
A low pressure sodium vapor discharge lamp for generating directional light output, the lamp including a cylindrical discharge tube within a cylindrical outer envelope.
The outer envelope is provided with a diffuse coating which is highly reflective of visible sodium light and which defines a clear aperture on the outer envelope for the directional escape of visible light.
The space between the inner discharge tube and the outer envelope is air filled to provide conductive and convective heat dissipation from the discharge tube.
Sodium condensation takes place in a plurality of spaced reservoirs located in the portion of the discharge tube away from the aperture to keep that portion of the discharge tube facing the aperture clear.
A heater coil is wound around the inner discharge tube to keep it at a desired standby temperature for lamp use on demand. The lamp filament electrodes are also maintained at standby temperature to improve the illumination profile along the lamp.
Description
2~
This inYention relates to a low pressure sodium vapor discharge lamp.
Prior art low pressure sodium vapor lamps, from which the present invention i5 to be disltinguished, are typically operated at relatively low power and it is generally desired to retain the heat generated within the lamp -to maintain ef*iciency. Additionally, su~h lamps typically emit in all directions for such purposes as street lighting or general illumination.
Sodium vapor illumination has certain advantages for use in xerography. For producing black and white copy, the monochromatic object illumination from a sodium vapor lamp produces the maximum in object contrast for exposure to a photoreceptor. This subject matter is more fully developed in U.S. Patent No. 3,869,205, issued to Charles F.
Gallo sn March 4, lg75.
It is an object of the present invention to provide a low pressure sodium vapor lamp capable of operation at relatively high power levels for correspondingly high intensity of light output, such light output being of controlled directionality.
In accordance with one aspect of this invention there is provided a low pressure sodium vapor discharge lamp for high intensity illumination of an object in a xero-graphic system, said lamp including:
a cylindrical outer envelope defining a cavity therein;
a cylindrical sodium vapor discharge tube disposed within said cavity;
said outer envelope including on the interior thereof a diffuse light-reflective coating for the inward reflection of ~ight inciden-t thereon from said discharge .. :, -1-, ~i$~
tube;
said light-reflective coating defining a clear aperture lengthwise along said outer envelope for the directional escape of visible light;
said outer envelope also containing air at atmospheric pressure whereby thermal convection and con-duction currents are established within said outex envelope;
and :~
said discharge tube including on tha surface . 10 thereof a plurality of protrusions defining a plurality of concave reservoirs within said discharge tube for the deposit of metallia sodium when said lamp is inoperative and condensed excess sodium when said lamp is operative.
For a better understanding of this inv~ntion, reference is made to the following re detailed descriptlon of an exemplary embodiment, given in connection with the accompanying drawing.
,~
-la-~.~ ..
, ,..,~ .
DRAWING
Figure 1 is a longitudinal cross section of ~-a lamp according to this invention.
Figure 2 is an axial cross section of the lamp of Figure 1, taken through its centralportion.
DESCRIPTION
Referring now to Figure 1, a low pressure sodium vapor discharge lamp is generally indicated at 2 and includes an inner discharge tube 4 mounted within an outer envelope 6 means of a suitable support structure shown schematically at 8. Electrodes 10 and 12 at opposite ends of the discharge tube are operatively connected respectively to electrical connection elements 14 and 16.
Referring now to Figure 2, lamp 2 including inner discharge tube 4 and outer envelope 6~ is shown in an axial cross section. ~s is more clearly shown in this view, outer envelope 6 is coated with a difusely reflective coating 18 defining a generally straight light aperture 20 along the length of the envelope 6. Examples of diffuse coating materials for coating 18 are titanium dioxide (Ti2~, barium sulfate (BaSO4), and magnesium oxide ~MgO). Aperture 20 can be sized to suit the require-ments of a particular system. In general, the aperture angle, that is the angle subtended by the aperture at the axis of the envelope, will be smaller than 180.
An aperture angle of roughly 60 is an exemplary configura-tion by a lamp used as a xerographic exposure light source.
The effect of the apertured reflective coating 18 on the envelope 6 is to inwardly reflect light generated by the discharge tube 4 so that it ultimately exits or escapes the lamp in the desired direction through the ' : :
2~
aperture 20.
In operation, when an electrical discharge is passed through the sodium vapor in the discharge tube 4, radiation is emitted in both the visihle and infrared portion of the spectrum. As is well known, the visible radiation is essentially mono-chromatic, nominally at 589.3 nm. Typically, the operating temperature at the wall of the discharge tube is approximately 2600C. In the prior art, for the sake cf efficiency, the in;Erared radia-tion from the lamp tube is conserved in the system, as by reflective inwards, to help keep the discharge tube at its optimum opexating temperature. By contrast to the prior art, the purpose of the present lamp is to operate at sub-stantially increased power levels for the purpose of maximizing output ligh-t intensity, albeit at a sacrifice of efficiency. ~ow in order to permit operation at such higher power levels, it is no longer desirable to conserve the heat generated by the lamp;
-- ~ rather it is desired to dissipate it~.
;~, c~ Sl (~ec~
In order to achieve the de~ed heat dissipation or heat transmission away from the discharge tube 4, -the envelope 6 is air or gas filled, ra~her than evacuated as in the prior art, to permit heat transmission by conduction and convection through the air as well as by radiation through the space. For air illing the outer envelope 6 is simply provided with one or more small ~p~ rcS
~` a~e#h~es 22 so tha-t the interior space 24 is in communication with the surrounding air. The higher power level of operation permitted by the addition of air effects a substantially greater intensity of visible light output of the lamp. At the same time, the reflective coating provides directionality to the light output.
These are of course desired conditions for use o~ a sodium discharge lamp as an exposure lamp in a xerographic system. The increased light intensity enables the associated xerographic process to be operated at correspondingly higher speed, and the tailored illumin~
ation profile permits imp~oved efficiency of object illumination.
Althou~h the heat dissipation or cooling effect can be achieved with different ~ases at different pressures, it is especially convenient to leave the outer envelope open to atmospheric air sinc e this minimized constructional detail and expense.
It order ta control and confine the loca-tion of condensed ~sodium within the discharge tube, protruding sodium reservoirs or "dimples" ~6 are constructed on the discharge tube 4. These dimple protrusi.ons tend to be cooler and are filled with an excess of %~
metallic sodium. In operation, the discharge tube is hot and the small amount of sodium is vaporized and serves as the radiating species of the gas discharge medium.
To ensure that the radiation is reasonably uniform along the length of the discharge tube, the dimples are uniformly distributed along the tube length. To the extent just described, these dimples are known to the prior art.
In the present invention, however, in order to ensure that the dimples remain comparatively cool so as to confine and localize in the "down" position as defined by gravity, preferably at or near the gravitational vertical, there is a combined beneficial effect of the sodium dimples thus located and the air presence in the tube envelope cavity 24. That is, to the extent that there is heat convection within the cavity 2~, the lower part of the tube 4 is cooler than the top part where the light aperture 20 is located. Thus, the portion of the discharge tube facing the aperture is kept clear of condensation of opaque sodium.
From a cold start, it takes an appreciable length of time for a sodium vapor lamp to warm up to its optimum operating temperature. For xerographic application, ~
it is desirable that the fill radiant output of the lamp be available on demand. To achieve this, the inner dis-charge tube is heated by auxiliary means. In a preferred embodiment, the discharge tube is wrapped with heater wire 28 which is independently powered. Thus, during warm-up and standby the heater wires are energi~ed while the lamp itself is off.
When the lamp is energized for use, the heater wires may be shut of. For some applications, where it is desirable -to operate the lamp at currents which do not produce the optimum discharge temperature, simultaneous application of both lamp and heater power can be used to produce the desired optimum tube temperature. The diameter and resistivity of the heater wire are selected 50 that the required .
power is conveniently obtained while minimizing the wire temperature and thermal gradients. In one exemplary and successful combination, Alumel wire of 0.01" diameter, was wound : r -4a around the discharge tube 4 in a helix o approximately 1/2" pitch.
With respect to the thermal coupling between -the heater wire and the discharge tube, there is a beneficial ef:Eect ~rom the combina-tion of the heater wire and the air in the CclVity 24, while in theconventional evacuated outer cavity, the thermal coupling between the heater wire and the discharge tube is quite poor resulting in thermal gradients along the discharge tube and sometimes glass cracking, in the present case the air puts the heater wires in better thermal contact with the discharge tube to reduce the - . thermal gradients therealong. ~he presence of air permits rela tively straightforward wrapping o the heater wire around the discharge tube. Otherwise, more elaborate and expensive construc-tional techniques would be necessary.
In typical sodium vapor lamps of the prior art, the lamp fila-ment electro.des are not externally heated. This could result in -the lamp ends being somewhat cooler than the lamp central portion with the possibility of a resulting correspondingly lower sodium vapor pressure and a resultant drop in the radiant proile at the ends.
In the present invention, the filament electrodes 10 and 12 are externally powered, indepenaently of the lamp discharge,. to provide ohmic heating to keep them appropriately warm at all times. This technique improves the longitudinal radiant proile of the la~p.
In addition, for xerographic application in which on-of lamp cycling is frequent, the life of the filament electrodes is extended by keeping them hot independent of lamp operation.
. The foregoing description of an embodiment of this invention is geven by way of illustration and not of limitation. The con-cept and scope of the invention are limited only by the following claims and equivalents thereof which may occur to others skilled in the art.
(S )
This inYention relates to a low pressure sodium vapor discharge lamp.
Prior art low pressure sodium vapor lamps, from which the present invention i5 to be disltinguished, are typically operated at relatively low power and it is generally desired to retain the heat generated within the lamp -to maintain ef*iciency. Additionally, su~h lamps typically emit in all directions for such purposes as street lighting or general illumination.
Sodium vapor illumination has certain advantages for use in xerography. For producing black and white copy, the monochromatic object illumination from a sodium vapor lamp produces the maximum in object contrast for exposure to a photoreceptor. This subject matter is more fully developed in U.S. Patent No. 3,869,205, issued to Charles F.
Gallo sn March 4, lg75.
It is an object of the present invention to provide a low pressure sodium vapor lamp capable of operation at relatively high power levels for correspondingly high intensity of light output, such light output being of controlled directionality.
In accordance with one aspect of this invention there is provided a low pressure sodium vapor discharge lamp for high intensity illumination of an object in a xero-graphic system, said lamp including:
a cylindrical outer envelope defining a cavity therein;
a cylindrical sodium vapor discharge tube disposed within said cavity;
said outer envelope including on the interior thereof a diffuse light-reflective coating for the inward reflection of ~ight inciden-t thereon from said discharge .. :, -1-, ~i$~
tube;
said light-reflective coating defining a clear aperture lengthwise along said outer envelope for the directional escape of visible light;
said outer envelope also containing air at atmospheric pressure whereby thermal convection and con-duction currents are established within said outex envelope;
and :~
said discharge tube including on tha surface . 10 thereof a plurality of protrusions defining a plurality of concave reservoirs within said discharge tube for the deposit of metallia sodium when said lamp is inoperative and condensed excess sodium when said lamp is operative.
For a better understanding of this inv~ntion, reference is made to the following re detailed descriptlon of an exemplary embodiment, given in connection with the accompanying drawing.
,~
-la-~.~ ..
, ,..,~ .
DRAWING
Figure 1 is a longitudinal cross section of ~-a lamp according to this invention.
Figure 2 is an axial cross section of the lamp of Figure 1, taken through its centralportion.
DESCRIPTION
Referring now to Figure 1, a low pressure sodium vapor discharge lamp is generally indicated at 2 and includes an inner discharge tube 4 mounted within an outer envelope 6 means of a suitable support structure shown schematically at 8. Electrodes 10 and 12 at opposite ends of the discharge tube are operatively connected respectively to electrical connection elements 14 and 16.
Referring now to Figure 2, lamp 2 including inner discharge tube 4 and outer envelope 6~ is shown in an axial cross section. ~s is more clearly shown in this view, outer envelope 6 is coated with a difusely reflective coating 18 defining a generally straight light aperture 20 along the length of the envelope 6. Examples of diffuse coating materials for coating 18 are titanium dioxide (Ti2~, barium sulfate (BaSO4), and magnesium oxide ~MgO). Aperture 20 can be sized to suit the require-ments of a particular system. In general, the aperture angle, that is the angle subtended by the aperture at the axis of the envelope, will be smaller than 180.
An aperture angle of roughly 60 is an exemplary configura-tion by a lamp used as a xerographic exposure light source.
The effect of the apertured reflective coating 18 on the envelope 6 is to inwardly reflect light generated by the discharge tube 4 so that it ultimately exits or escapes the lamp in the desired direction through the ' : :
2~
aperture 20.
In operation, when an electrical discharge is passed through the sodium vapor in the discharge tube 4, radiation is emitted in both the visihle and infrared portion of the spectrum. As is well known, the visible radiation is essentially mono-chromatic, nominally at 589.3 nm. Typically, the operating temperature at the wall of the discharge tube is approximately 2600C. In the prior art, for the sake cf efficiency, the in;Erared radia-tion from the lamp tube is conserved in the system, as by reflective inwards, to help keep the discharge tube at its optimum opexating temperature. By contrast to the prior art, the purpose of the present lamp is to operate at sub-stantially increased power levels for the purpose of maximizing output ligh-t intensity, albeit at a sacrifice of efficiency. ~ow in order to permit operation at such higher power levels, it is no longer desirable to conserve the heat generated by the lamp;
-- ~ rather it is desired to dissipate it~.
;~, c~ Sl (~ec~
In order to achieve the de~ed heat dissipation or heat transmission away from the discharge tube 4, -the envelope 6 is air or gas filled, ra~her than evacuated as in the prior art, to permit heat transmission by conduction and convection through the air as well as by radiation through the space. For air illing the outer envelope 6 is simply provided with one or more small ~p~ rcS
~` a~e#h~es 22 so tha-t the interior space 24 is in communication with the surrounding air. The higher power level of operation permitted by the addition of air effects a substantially greater intensity of visible light output of the lamp. At the same time, the reflective coating provides directionality to the light output.
These are of course desired conditions for use o~ a sodium discharge lamp as an exposure lamp in a xerographic system. The increased light intensity enables the associated xerographic process to be operated at correspondingly higher speed, and the tailored illumin~
ation profile permits imp~oved efficiency of object illumination.
Althou~h the heat dissipation or cooling effect can be achieved with different ~ases at different pressures, it is especially convenient to leave the outer envelope open to atmospheric air sinc e this minimized constructional detail and expense.
It order ta control and confine the loca-tion of condensed ~sodium within the discharge tube, protruding sodium reservoirs or "dimples" ~6 are constructed on the discharge tube 4. These dimple protrusi.ons tend to be cooler and are filled with an excess of %~
metallic sodium. In operation, the discharge tube is hot and the small amount of sodium is vaporized and serves as the radiating species of the gas discharge medium.
To ensure that the radiation is reasonably uniform along the length of the discharge tube, the dimples are uniformly distributed along the tube length. To the extent just described, these dimples are known to the prior art.
In the present invention, however, in order to ensure that the dimples remain comparatively cool so as to confine and localize in the "down" position as defined by gravity, preferably at or near the gravitational vertical, there is a combined beneficial effect of the sodium dimples thus located and the air presence in the tube envelope cavity 24. That is, to the extent that there is heat convection within the cavity 2~, the lower part of the tube 4 is cooler than the top part where the light aperture 20 is located. Thus, the portion of the discharge tube facing the aperture is kept clear of condensation of opaque sodium.
From a cold start, it takes an appreciable length of time for a sodium vapor lamp to warm up to its optimum operating temperature. For xerographic application, ~
it is desirable that the fill radiant output of the lamp be available on demand. To achieve this, the inner dis-charge tube is heated by auxiliary means. In a preferred embodiment, the discharge tube is wrapped with heater wire 28 which is independently powered. Thus, during warm-up and standby the heater wires are energi~ed while the lamp itself is off.
When the lamp is energized for use, the heater wires may be shut of. For some applications, where it is desirable -to operate the lamp at currents which do not produce the optimum discharge temperature, simultaneous application of both lamp and heater power can be used to produce the desired optimum tube temperature. The diameter and resistivity of the heater wire are selected 50 that the required .
power is conveniently obtained while minimizing the wire temperature and thermal gradients. In one exemplary and successful combination, Alumel wire of 0.01" diameter, was wound : r -4a around the discharge tube 4 in a helix o approximately 1/2" pitch.
With respect to the thermal coupling between -the heater wire and the discharge tube, there is a beneficial ef:Eect ~rom the combina-tion of the heater wire and the air in the CclVity 24, while in theconventional evacuated outer cavity, the thermal coupling between the heater wire and the discharge tube is quite poor resulting in thermal gradients along the discharge tube and sometimes glass cracking, in the present case the air puts the heater wires in better thermal contact with the discharge tube to reduce the - . thermal gradients therealong. ~he presence of air permits rela tively straightforward wrapping o the heater wire around the discharge tube. Otherwise, more elaborate and expensive construc-tional techniques would be necessary.
In typical sodium vapor lamps of the prior art, the lamp fila-ment electro.des are not externally heated. This could result in -the lamp ends being somewhat cooler than the lamp central portion with the possibility of a resulting correspondingly lower sodium vapor pressure and a resultant drop in the radiant proile at the ends.
In the present invention, the filament electrodes 10 and 12 are externally powered, indepenaently of the lamp discharge,. to provide ohmic heating to keep them appropriately warm at all times. This technique improves the longitudinal radiant proile of the la~p.
In addition, for xerographic application in which on-of lamp cycling is frequent, the life of the filament electrodes is extended by keeping them hot independent of lamp operation.
. The foregoing description of an embodiment of this invention is geven by way of illustration and not of limitation. The con-cept and scope of the invention are limited only by the following claims and equivalents thereof which may occur to others skilled in the art.
(S )
Claims (3)
1. A low pressure sodium vapor discharge lamp for high intensity illumination of an object in a xero-graphic system, said lamp including:
a cylindrical outer envelope defining a cavity therein;
a cylindrical sodium vapor discharge tube disposed within said cavity;
said outer envelope including on the interior thereof a diffuse light-reflective coating for the inward reflection of light incident thereon from said discharge tube;
said light-reflective coating defining a clear aperture lengthwise along said outer envelope for the directional escape of visible light;
said outer envelope also containing air at atmospheric pressure whereby thermal convection and con-duction currents are established within said outer envelope;
and said discharge tube including on the surface thereof a plurality of protrusions defining a plurality of concave reservoirs within said discharge tube for the deposit of metallic sodium when said lamp is inoperative and condensed excess sodium when said lamp is operative.
a cylindrical outer envelope defining a cavity therein;
a cylindrical sodium vapor discharge tube disposed within said cavity;
said outer envelope including on the interior thereof a diffuse light-reflective coating for the inward reflection of light incident thereon from said discharge tube;
said light-reflective coating defining a clear aperture lengthwise along said outer envelope for the directional escape of visible light;
said outer envelope also containing air at atmospheric pressure whereby thermal convection and con-duction currents are established within said outer envelope;
and said discharge tube including on the surface thereof a plurality of protrusions defining a plurality of concave reservoirs within said discharge tube for the deposit of metallic sodium when said lamp is inoperative and condensed excess sodium when said lamp is operative.
2. A low pressure sodium vapor discharge lamp according to claim 1 and further including means for ener-gizing said tube to create an operating temperature of approximately 260°C at the wall of said tube, said energizing means including a warm-up resistive wire wound around said tube and in contact therewith.
3. A low pressure sodium vapor discharge lamp as claimed in claim 2 wherein said protrusions are disposed on the surface of said discharge tube generally in and away from said clear aperture to attract sodium condensation away from said clear aperture.
Applications Claiming Priority (10)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US79598877A | 1977-05-11 | 1977-05-11 | |
| US79597677A | 1977-05-11 | 1977-05-11 | |
| US79598777A | 1977-05-11 | 1977-05-11 | |
| US79598577A | 1977-05-11 | 1977-05-11 | |
| US79598677A | 1977-05-11 | 1977-05-11 | |
| US795,985 | 1977-05-11 | ||
| US795,987 | 1977-05-11 | ||
| US795,988 | 1977-05-11 | ||
| US795,986 | 1977-05-11 | ||
| US795,976 | 1991-11-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1108214A true CA1108214A (en) | 1981-09-01 |
Family
ID=27542213
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA303,069A Expired CA1108214A (en) | 1977-05-11 | 1978-05-10 | Low pressure sodium vapor discharge lamp |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS53139376A (en) |
| CA (1) | CA1108214A (en) |
| GB (1) | GB1597794A (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE458365B (en) * | 1987-04-27 | 1989-03-20 | Lumalampan Ab | GAS EMISSIONS LAMP OF METAL TYPE |
| DE10021510A1 (en) * | 2000-05-03 | 2001-11-08 | Mannesmann Vdo Ag | Lighting device, especially cold cathode lamp with electrical heating, e.g. for LCD display in motor vehicle, uses heating wire which multiply crosses one face of cold cathode lamp |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5234868B2 (en) * | 1971-11-09 | 1977-09-06 | ||
| JPS5233906B2 (en) * | 1972-02-15 | 1977-08-31 |
-
1978
- 1978-05-04 JP JP5286178A patent/JPS53139376A/en active Pending
- 1978-05-08 GB GB1828178A patent/GB1597794A/en not_active Expired
- 1978-05-10 CA CA303,069A patent/CA1108214A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| GB1597794A (en) | 1981-09-09 |
| JPS53139376A (en) | 1978-12-05 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |