COMPACT FLUORESCENT LAMP Field of the invention
The present invention relates to a compact fluorescent lamp and to a method of manufacture thereof Background of the invention
Fluorescent lamps that utilize a fluorescent coating in a glass tube and a gas filling capable of being charged to produce ultraviolet energy in order to energize the fluorescent coating have been used for a long time. The conventional fluorescent lamps are normally supphed in the form of elongated tubes of significant length, for instance, between 2 ft and 4 ft, and require a large installation space and large fixtures for holding such lamps. The bulkiness of the lamps and fixtures required in the case of conventional fluorescent lamps has been a major drawback in their domestic utilization where space available for utilization is often less. As a result, the energy saving aspect of the fluorescent lamps has therefore not been fully utilized in the domestic consumer market.
Several attempts have been made in recent years to use compact fluorescent lamps to replace conventional incandescent lamps due to their high energy saving features. Another benefit of using fluorescent lamps is their longer lifetime when compared to the incandescent lamps. More compact fluorescent lamps are now widely available shaped generally in a plurality of parallel extending tubes from a base at a predetermined length. However, such compact fluorescent lamps though now readily available for domestic commercial application are also limited in their use due to their big size and high cost of manufacture and their low lumen output.
As explained above, a significant disadvantage of available compact fluorescent lamps for use in domestic consumer market is the size that is big when compared to that from the incandescent lamps. For example, in order to obtain the same lumen output as a conventional 60-watt incandescent bulb in a 12-15W Conventional Compact Fluorescent Lamp of about 130-160mm is required. In order to produce the similar level of Lumen the lamp Arc Length is generally used to maximize the lumens. It is evident that a significant problem faced is that of packaging a long tube within a small package size such that it fits in a conventional incandescent lamp fixture.
Low-pressure discharge lamps are well known in the art. These lamps contain -small doses of mercury, which radiates under the influence of the discharge arc. In

order to accomplish maximum light output, it is desirable to make the discharge tube of the lamp as long as possible, which results in a large luminous surface. At the same time, to accomplish light outputs comparable to the light output of a traditional incandescent bulb requires the application of discharge tubes with a length in excess of tens of centimeters. Such tubes require to be folded into various forms in order to make them compact enough for various lamp shades and covers which were originally designed for incandescent bulbs.
It is known to divide a long discharge tube into shorter sections, and to dispose the sections in a parallel configuration around a common central axis. As an example, a 60 cm long discharge tube may be divided into six sections, each ten centimeter long. The tubes are connected to each other through connecting necks, alternating at the top end or bottom end of the tubes. This configuration has the advantage of utilizing a relatively large surface area of the tube sections because the adjacent tubes leave approximately two thirds of the tube surface visible from the outside of the lamp. This part of the tube surface may be considered as the effective tube surface. However, this parallel configuration is still too long for many applications because the housing of the lamp, which normally contains the ballast electronics, also adds to the overall length of the discharge lamp. Further, the discharge arc exerts non-uniform load on the discharge tube which adversely affects the light output and the lifetime of the lamp.
One solution attempted by several lamp manufacturers is to extend the length of the respective tube portions in a lamp envelope, or alternatively increase the number of tube portions to as many as eight such tube portions arranged side-by-side. One example of such application produced fluorescent lamps by bending segments of glass tubes into U-shapes and sealing of one or both legs and then connecting two or more of such bent tubes with glass bridges by simultaneously blowing out a small hole near one end of the tube and then fusing them together. For instance, in a dual U-shaped lamp, the arc discharge passageway goes up one leg, down the other and then through the glass bridge into a second bent tube arrangement.
US Patent 5,252,890 discloses a compact type fluorescent lamp device that has a crooked arc path. The bulb used is a reversed W-shaped arc bulb which includes a first and second U-shaped bulb. The reverse W-shaped arc bulb is fabricated by first heating the outside surface of one of the ends of a first U-shaped bulb and the corresponding surface of one of the ends of a second U-shaped bulb. The heated
portions are closely opposed and connected to one another in a blow-off process to fluidly communicate to each other. A first electrode is disposed in one end of the first U-shaped bulb, and a second electrode is arranged in the other end. A substantially W-shaped arc path is thus formed in the connected first and second U-shaped bulbs. A wide recess is formed at the center of the pedestal portion of the base in order to house the connected portion of the first and second U-shaped bulbs. The process further requires the formation of a pair of holes at the opposite sides of the wide recess in the pedestal portion. The other ends of the first and second U-shaped bulbs in which the first and second electrodes are disposed are respectively inserted into the corresponding holes, and are further supported with an elastic bonding agent which is later filled in the pedestal portion. The reversed W-shaped arc bulb therefore requires elaborate manufacturing steps for blowing-off portions of the glass tubes and then reconnecting them to provide fluid communication between the two U-shaped bulbs. It is an expensive manufacturing process and the product produced must be marketed at a high cost basis.
In this conventional construction of multiple-tube design, three separate passageways must be provided in connecting the four tubes together such that a single arc path can be obtained. The building of four individual tubes and the connections that must be made there between render the manufacturing process difficult and costly.
A double helix-shaped compact fluorescent lamp is disclosed in U.S. Pat. No. 5,705,883. Such a double helix configuration results in a much more compact discharge tube, and the overall length of a coil with a total length of approximately 60 cm can be reduced to six centimeters, instead of the ten centimeters necessary for the parallel configuration. However, the effective lighting area of the discharge tube is reduced, because approximately one half of the discharge tube surface is visible only to the outside apart from the top turn of the helix. Therefore, the luminous efficacy of this known lamp is not completely satisfactory.
US Patent 5,705,883 discloses a double helix formed by the discharge tube and having an essentially constant inner and outer diameter, apart from the sealed ends of the discharge tube which are bent inwards. The bending of the tube ends is made in a separate manufacturing step. The bending of the ends does not influence the effective surface of the discharge tube, as the bent ends are inserted into a supporting housing.
German Patent Application No. DE 41 33 077 discloses another double helix shaped discharge lamp. In this known discharge lamp, there is a cold chamber positioned at the top of the lamp between the two ends of the tube portions constituting the strands of the double spiral. There is a relatively large distance between the turns of the two strands of the helix, so that the surface of the discharge tube turning inwards is also partly visible, adding to the effective area. However, the large distance between the turns again results in a large longitudinal dimension of the coil to the detriment of the overall compactness of the lamp.
Another double helix shaped compact fluorescent lamp is disclosed in the document WO 94/29895. The double helix of this lamp has a central section and an end section. The sealed ends of the discharge tube are disposed at the end section. The inner diameter of the central section of the helix is smaller than the inner diameter of the end section. As a result, the overall lighting efficiency of the discharge tube does not surpass that of the discharge tube known from U.S. Pat. No. 5,705,883, while achieving shorter total discharge tube length due to the gradually decreasing diameter of the coil, and as a result, decreased light output. Generally, the lighting efficiency of this lamp has the same problems as the above mentioned lamps known from U.S. Pat. No. 5,705,883 and from German Patent Application No. DE 41 33 077. The compactness of the lamp is also less satisfactory, because the sealed ends add to the total length of the coiled discharge tube.
US Patent 6759797 discloses a compact fluorescent lamp with a double helix shaped discharge tube in which the two strands of the helix are constituted by two helix shaped tube portions. These tube portions define a central axis of the discharge tube. The double helix formed by the discharge tube has a central section and a first end section. These sections are defined along the central axis, and the lamp base for receiving ends of the tube portions is disposed at the first end section. An inner diameter of the central section of the helix is larger than an inner diameter of the first end section. The discharge tube of this patent is manufactured using a radially segmented molding core. Once the coiling of the discharge tube on the molding core is completed, the segmented molding core is shrunk radially, and then is withdrawn from the coiled discharge tube axially.
Therefore, there is a need for a discharge lamp which exhibits improved lighting efficiency combined with compact dimensions of the coiled discharge tube, particularly a short overall length of the coil formed by the discharge tube.
Objects of the invention
The main object of the invention is to provide a compact fluorescent lamp which while maintaining its energy saving properties possesses a higher lumen output than conventional fluorescent lamp while exhibiting longer shelf life.
It is another object of the invention to provide a compact fluorescent lamp which is simple and inexpensive to manufacture compared to conventional compact florescent lamps.
It is yet another object of the invention to provide a compact fluorescent lamp which is simple and inexpensive to manufacture without compromising on properties of energy saving and shelf life and lumen output and is suitable for domestic consumer use.
It is another object of the invention to provide a compact fluorescent lamp which is same or smaller in size compared to a normal Incandescent House Hold bulb commonly used but it should provide same or more lumen output. Summary of the invention
As explained above, compact fluorescent lamps are available in various shapes such as 1/2/3/4U and Spiral type. These lamps are used as replacement for conventional incandescent lamps due to their energy saving properties. However, a significant for their limited use is in their relatively larger size compared to conventional incandescent lamps as well as their low lumen output.
Accordingly the present invention provides a compact fluorescent lamp comprising of a double helix shaped discharge tube including two helix shaped tube portions, the tube portions defining a central axis of the discharge tube, the double helix having a central section and a first end section, the sections of the helix being defined along the central axis, a lamp support unit being provided connected to the discharge tube through connection means corresponding with the respective end sections of the double helix discharge tube, the support unit being provided with ventilation means adjacent said connection means, one or more ribs being provided in a predetermined manner in order to enable ventilation access for heat dissipation while maintaining the safety, a base means comprising a first end and a second end being provided and connected to the support means through said first end, the second end being engage able in a lamp holder.
In one embodiment of the invention, the ventilation means comprises one or more louver type apertures provided adjacent to the tube connecting means.
In yet another embodiment of the invention, the ventilation means are provided between the tube connecting means and the periphery of the support.
In another embodiment of the invention, the ribs are provided in a linear manner between the ventilation means and tube connecting means.
In another embodiment of the invention, the base means comprises housing with a first end and a second end the housing being adapted to accommodate the electronic components of the lamp therein.
In yet another embodiment of the invention, the base has a height in the range of 27-32mm.
In another embodiment of the invention, the diameter of the tube portions is substantially constant.
In another embodiment of the invention, the double helix has an external configuration which is substantially spherical.
In another embodiment of the invention, the double helix has an external configuration which is substantially barrel-shaped.
In another embodiment of the invention, the double helix has an external configuration which is substantially elhpsoidal.
In another embodiment of the invention, the tube diameter is in the range of 6.5-8.0 mm in order to reduce the length of the lamp.
In another embodiment of the invention, the length of the tube leg after bending is in the range of 6-16 mm to keep the lamp length lower.
In another embodiment of the invention, the spacing between the bend glass in the range of 2.0 to 3.0mm to reduce and optimize the containment of lamp lumen inside the discharge tubes.
In another embodiment of the invention, the base diameter is in the range of 29- 34 mm. Brief description of the accompanying drawings
Figure 1 is a schematic representation of a conventional compact fluorescent lamp in exploded form.
Figure 2 is a schematic representafion of the compact fluorescent lamp of the invention in exploded form.
Figure 3 is a schematic representation of a conventional double helix type compact fluorescent lamp as manufactured.
Figure 4a is a schematic representation of the tube of the compact fluorescent lamp of the invention.
Figure 4b is a schematic representation of the base used in the compact fluorescent lamp of the invention.
Figure 4c is a schematic representation of the tube support unit used in the compact fluorescent lamp of the invention. Detailed description of the invention
The compact fluorescent lamp- of the invention will now be described with reference to the accompanying drawings. Figure 2 is a schematic representation of the compact fluorescent lamp of the invention in exploded form. In Figure 2 the double helix shaped discharge tube (1) includes two helix shaped tube portions (la, lb), the tube portions defining a central axis of the discharge tube, the double hehx having a central section (1c) and ending in end sections (Id), the sections of the helix being defined along the central axis, a lamp support unit (2) being provided connected to the discharge tube (1) through connection means (3) corresponding with the respective end sections (1d) of the double helix discharge tube (1), the support unit (2) being provided with ventilation means (4) adjacent said connection means (3), one or more ribs (5) being provided in a predetermined manner in order to enable ventilation access for heat dissipation, a base means (6) comprising a first end (6a) and a second end (6b) being provided and connected to the support means (2) through said first end (6a), the second end (6b) being engage able in a lamp holder.
Figure 3 is a schematic representation of the compact fluorescent lamp of the invention as manufactured. The base unit housing (21) is connected to a tube support means (22) which in turn is connected to the discharge tube (23).
Figure 1 is a schematic representation of a conventional compact fluorescent lamp. As can be clearly seen, such conventional lamps do not possess ventilation apertures or plastic ribs to provide ventilation access in the gluing area. In addition the leg portions of the discharge tube are longer and the bend width in the tubes is also greater leading to a longer and bulkier tube.
Figure 4a is a schematic representation of the tube of the compact fluorescent lamp of the invention.
Figure 4b is a schematic representation of the base unit (6 of Fig 1) and comprises a housing (21) with a first end (22) and a second end (23) the housing
being adapted to accommodate the electronic components of the lamp therein. The base has a height in the range of 29-34 mm.
The ventilation means is shown in Figure 4c and comprises one or more louver type apertures provided adjacent to the tube connecting means. The ventilation means are preferably provided between the tube connecting means and the periphery of the support. The ribs are provided in a linear manner between the ventilation means and tube connecting means.
In the compact fluorescent lamp of the invention, the diameter of the tube portions is substantially constant. The double helix has an external configuration which is substantially spherical, substantially barrel-shaped or substantially ellipsoidal. The tube diameter is in the range of 6.5-8.0 mm in order to reduce the length of the lamp. The length of the tube leg after bending is in the range of 6-16 mm to keep the lamp length lower. The spacing between the bend glass in the range of 2.0 to 3.0mm to reduce and optimize the containment of lamp lumen inside the discharge tubes. The base diameter is in the range of 29-34 mm.
It is observed that the compact fluorescent lamp of the invention is similar than a conventional incandescent lamp while retaining up to 75-80% energy saving properties and 4-6 times hfe that of a conventional fluorescent lamp.
This is achieved primarily by the following features
A Tube Diameter: The Glass tube diameter has been reduced from 9-12mm to 6.5-8.0 mm to reduce the length of the lamp.
B Shorter Leg Length: The length of the leg after bending generally used
is between 16-22 mm, which has been reduced to 6-16mm to keep the lamp length lower.
C Spacing between Bend Glass: This has been optimized after various
test & kept between 2.0 to 3.0mm. This would help to reduce & optimize the containment of lamp lumen inside the Glass Tubes.
D Plastic base diameter: the plastic base diameter has been optimized between29-34mm keeping in view the electronic components requirements, aesthetics & fitment is the light fixture in view.
E Special Design ventilation Holes: The 2 nos. Special design louver
type hole are kept on both side of the lamp Insertion position. These holes help in proper cross ventilation in conjunction with holes in opposite direction (near the B22
cap fitment area). This is necessary so as to keep the life of the lamp intact which otherwise would have been effected due to the reduction in plastic size.
F Special design for gluing area: Two support of plastic Rib have been
added to contain the Glue/cement in specific useful area only. This has been kept for keeping the provision for the holes for lamp heat dissipation.
G Plastic Body Height: The plastic Body height has been fixed between 29-34 mm to optimize the heat dissipation, locating all electronic components inside the plastic.
H Plastic Support for lamp holding: This has been provided with height between 2.0-3.5mm to hold the lamp at the right position during the Gluing process.
Some of the particular features of the present invention involve using a special double coating wherein in order to achieve optimum lamp performance, an Alumina Oxide Pre-coating is provided before the Phosphor coating. This helps in reducing the liberation on Sodium Ions from the Glass. The Sodium Ion if continuously released from the Glass has negative impact on lamp lumens. The prior art methods rely on mixing the Alumina Oxide with the Phosphor powder to reduce this activity of Sodium Liberation. However, in the present invention, a double coat is used despite the small size, firstly with Alumina Oxide and then with Phosphor. It is observed that this assists in maintaining lamp lumen through the life of the lamp.
The coating method involves the use of special jigs to ensure uniform coatings. Conventional jigs and holding mechanism are replaced and modified and adapted in order to achieve quality of coating.
It must be understood that the foregoing description is illustrative of the invention and modifications are possible without departing from the scope and spirit of the invention and are intended to be covered herein.

We claim:
1. A compact fluorescent lamp comprising of a double helix shaped discharge tube including two helix shaped tube portions, the tube portions defining a central axis of the discharge tube, the double helix having a central section and a first end section, the sections of the helix being defined along the central axis, a lamp support unit being provided connected to the discharge tube through connection means corresponding with the respective end sections of the double helix discharge tube, the support unit being provided with ventilation means adjacent said connection means, one or more ribs being provided in a predetermined manner in order to enable ventilation access for heat dissipation, a base means comprising a first end and a second end being provided and connected to the support means through said first end, the second end being engage able in a lamp holder.
2. A compact fluorescent lamp as claimed in claim 1 wherein the ventilation means comprises one or more louver type apertures provided adjacent to the tube connecting means.
3. A compact fluorescent lamp as claimed in claim 1 and 2 wherein the ventilation means are provided between the tube connecting means and the periphery of the support.
4. A compact fluorescent lamp as claimed in claim 1 to 3 wherein the ribs are provided in a linear manner between the ventilation means and tube connecting means.
5. A compact fluorescent lamp as claimed in any preceding claim wherein the base means comprises a housing with a first end and a second end the housing being adapted to accommodate the electronic components of the lamp therein.
6. A compact fluorescent lamp as claimed in claim 5 wherein the base has a height in the range of 29-34mm.
7. A compact fluorescent lamp as claimed in claim 1 wherein the double helix discharge tube is provided with a second end section the second end section being opposite to the lamp base, and an inner diameter of the central section of the helix is larger than an inner diameter of the second end section.
8. A compact fluorescent lamp as claimed in claim 1 wherein the diameter of the tube portions is substantially constant.
9. A compact fluorescent lamp as claimed in claim 1 wherein the double helix has an external configuration which is substantially spherical.
10. A compact fluorescent lamp as claimed in claim 1 wherein the double helix has an external configuration which is substantially barrel-shaped.
11. A compact fluorescent lamp as claimed in claim 1 wherein the double helix has an external configuration which is substantially ellipsoidal.
12. A compact fluorescent lamp as claimed in claim 1 wherein the tube diameter is in the range of 6.5-8.0 mm in order to reduce the length of the lamp.
13. A compact fluorescent lamp as claimed in claim 1 wherein length of the tube leg after bending is in the range of 6-15 mm to keep the lamp length lower.
14. A compact fluorescent lamp as claimed in claim 1 wherein spacing between the bend glass in the range of 2.0 to 3.0mm to reduce and optimize the containment of lamp lumen inside the discharge tubes.
15. A compact fluorescent lamp as claimed in claim 1 wherein the base diameter is in the range of 3 0-3 2mm.
16. A compact fluorescent lamp substantially as described hereinbefore and with reference to the accompanying drawings.