Electric lamp and discharge devices – With envelope – Having base and connector
Reexamination Certificate
2001-02-15
2004-11-09
Williams, Joseph (Department: 2879)
Electric lamp and discharge devices
With envelope
Having base and connector
C313S317000, C313S493000, C313S623000, C313S634000, C362S216000, C362S222000
Reexamination Certificate
active
06815879
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a circular fluorescent lamp having a tube with a small outer diameter, and a lighting fixture using the lamp.
2. Description of the Related Art
Generally, it is known that the luminous efficacy of a fluorescent lamp changes according to the mercury-vapor pressure ratio of the lamp. The mercury-vapor pressure is controlled by the temperature of a cold spot, which is the coldest portion of the fluorescent lamp during the lamp operation. When the temperature of the cold spot becomes high, more mercury evaporates, so that the luminous flux of the fluorescent lamp can increase. If the temperature of the cold spot becomes too high, then the luminous flux decreases, because, the in excess evaporated mercury absorbs ultraviolet rays generated in the fluorescent lamp, which are changed to visible light.
A circular fluorescent lamp, having an outer tube diameter of about 29 mm and an overall circular outer diameter of 225 mm, can appropriately maintain the cold spot temperature. However, recently, fluorescent lamps having a small tube outer diameter have become available. The temperature of the fluorescent lamp tends to increase because of the small volume of the tube, so that the cold spot can not be appropriately maintained at the proper temperature in the fluorescent lamp. Accordingly, the cold spot can not control the mercury-vapor pressure of the lamp, so that the luminous efficacy may be reduced.
In order to maintain the cold spot of the fluorescent lamp at the proper temperature, Japanese Laid Open Patent Application HEI 11-3682 discloses a circular fluorescent lamp having long and short stems, which seal opposite ends of the tube of the fluorescent lamp. That is, one stem including conductive wires and filament is longer than the other stem. As a result, the longer stem side of the fluorescent lamp has the cold spot. Since the filament generating heat near the long stem is far from the end of the tube as compared with that of the short stem, the end of the long stem of the tube is easily cooled during the lamp operation as compared with the other portions of the tube.
Such circular fluorescent lamp will be described in more detail by way of example shown in
FIG. 8
which shows an enlarged longitudinal section around the ends of a conventional fluorescent lamp. The circular fluorescent lamp
30
is provided with a circular tube
31
having a tube outer diameter of 16.5 mm. A pair of stems
32
,
33
seal respective ends of the tube
31
, which are accommodated by a lamp base
36
having pins
37
. Each of stems
32
,
33
comprises conductive wires
35
, and a filament
34
connected between conductive wires
35
. A length H
1
of one stem
32
is formed longer than a length H
2
of the other stem
33
. The lamp base
36
can rotate around the center axis of the circular tube
31
. In this case, when the in fluorescent lamp lights, the cold spot
38
occurs at the sealing portion associated with the stem
32
, because, the filament
34
generating heat is further apart from the sealing portion for the stem
32
.
The conductive wires
35
extended outwardly from the stem
32
are longer than those of the stem
33
. Furthermore, the outer conductive wires
35
of the stems
32
,
33
are loosely connected to the pins
37
. Accordingly, when the lamp base
36
is rotated about within +15 degrees to −15 degrees around the center axis of the tube
31
, each of the conductive wires
35
moves with the lamp base
36
. As a result, the conductive wires
35
occasionally touch each other. In particular, the touching occurs easily at the side of longer stem
32
because of the looseness of the long outer conductive wires
35
. As a result, conductive wires
35
are shorted. If a short circuit occurs, the electrical ballast may be damaged.
SUMMARY OF THE INVENTION
According to one aspect of the invention, a circular fluorescent lamp comprises a light-transmitting circular tube, filled with a discharge gas including mercury and a rare gas, having an outer tube diameter in the range of about 14 mm to about 18 mm. A phosphor layer is coated on the inner surface of the light-transmitting circular tube. Each of the stems, sealing opposite ends of the light-transmitting circular tube, holds a pair of conductive wires, of which one end of each is connected to a filament, and the other end of each extends outwardly from the circular tube. A lamp base, arranged between the ends of the light-transmitting circular tube so as to rotate slightly around the center axis of the circular tube, fixes conductive pins which are connected to the conductive wires. An insulator, arranged between the conductive wires, limits the movement of the conductive wires.
According to another aspect of the invention, a lighting fixture comprises the circular fluorescent lamp. A ballast supplies the electric power to the circular fluorescent lamp. The circular fluorescent lamp and the ballast are arranged in a body.
These and other aspects of the invention will be further described in the following drawings and detailed description of the invention.
REFERENCES:
patent: 4281238 (1981-07-01), Noma et al.
patent: 4324998 (1982-04-01), Gilmore et al.
patent: 4326146 (1982-04-01), Plagge et al.
patent: 4878854 (1989-11-01), Cannon
patent: 4949007 (1990-08-01), Takagi et al.
patent: 5796210 (1998-08-01), Sakakibara et al.
patent: 6286971 (2001-09-01), Hori
patent: 6342763 (2002-01-01), Fukushima et al.
patent: 06338289 (1994-12-01), None
patent: 11-3682 (1999-01-01), None
patent: 11162329 (1999-06-01), None
Matsunaga Yoshiyuki
Nakamura Toshiyuki
Roy Sikha
Toshiba Lighting & Technology Corporation
Williams Joseph
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