Fluorescent lamp having separate cooling means for ballast and fluorescent tube

A fluorescent lamp device according to the present invention includes a ballast, a screw base electrically connected to the ballast, a fluorescent tube curved in an arc at three portions thereof, a bowl-shaped member for housing the ballast with the screw base fixed projecting outside therefrom, a globe, and a partition plate attached to an open end of the member so as to thermally isolate or insulate the ballast from the fluorescent tube and to which the fluorescent tube is fixed. The bowl-shaped member is provided with a plurality of ventilating slits for discharging heat radiated from the ballast, and also with air-ducts for communicating the space inside the globe with the outside air. The globe is also provided with holes at the top portion thereof.

BACKGROUND OF THE INVENTION 
The present invention relates to a fluorescent lamp device and, more 
particularly, a fluorescent lamp device capable of being freely detachably 
connected to the external socket for an incandescent lamp and used instead 
of incandescent lamp. 
The fluorescent lamp which can be replaced instead of incandescent lamp has 
become popular these days. The fluorescent lamp of this type has a screw 
base which can be fitted into the incandescent lamp socket, and when the 
screw base is connected to the socket, the fluorescent lamp can be used in 
same manner as the incandescent lamp. 
In the conventional fluorescent lamp, a reactance ballast, starter circuit 
and the like are compactly housed together with a fluorescent tube, in a 
same space of an envelope which includes a bowl-shaped member and globe. 
When the fluorescent lamp is kept turned on, temperature in the globe 
rises undesirably due to heat generated from the ballast and the 
fluorescent tube, particularly heat radiated from the ballast. It is 
usually desirable that the fluorescent lamp is designed to achieve maximum 
fluorescent efficiency when temperature around the lamp is from 20.degree. 
C. to 25.degree. C. and tube wall temperature is about 40.degree. C. 
However, temperature in the envelope rises even up to 100.degree. C. 
because of heat mentioned above. As a result, the intensity of ultraviolet 
rays of the fluorescent tube and the intensity of visible rays radiated 
from fluorescent material coated on the inner surface of the tube are 
remarkably reduced to thereby lower the luminous efficacy of fluorescent 
lamp. 
The bowl shaped member and/or globe in the conventional fluorescent lamp 
are provided with a plurality of ventilating bores so as to eliminate the 
above-mentioned drawback. Air outside the lamp comes into the lamp through 
these ventilating bores and air of high temperature in the lamp flows 
outside the lamp through these ventilating bores. Temperature rise in the 
fluorescent tube kept lightening is thus improved a little. However, heat 
which is radiated from the reactance ballast and which corresponds to most 
of heat generated can not be expelled enough. In addition, fresh outside 
air entering into the globe through the ventilating bores is also heated 
by the reactance ballast. Therefore, temperature in the envelope can not 
be kept to the above-mentioned one optimum for the fluorescent tube. 
Particularly when the fluorescent lamp is used the screw base side down, 
heat radiated from the reactance ballast rises to hit the fluorescent tube 
directly. Therefore, heat discharge is not enough in the conventional 
fluorescent lamp and temperature in the lamp can not be lowered to the 
above-mentioned optimum one (or target one). It can not be expected 
therefore that the luminous efficacy of fluorescent lamp is enhanced 
satisfactorily. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a new and improved 
fluorescent lamp device capable of effectively preventing the rise of 
ambient temperature of fluorescent tube housed in the lamp so as to 
improve its luminous efficacy. 
A fluorescent lamp device according to the present invention has a 
fluorescent tube housed in an envelope and electrically connected to a 
ballast and is fitted into an external socket when used. The fluorescent 
tube is bent at at least one position thereof to a predetermined form. The 
ballast is thermally insulated from the fluorescent tube in the envelope. 
The fluorescent tube is contacted at least partially and directly with air 
outside independently of the ballast. Thus, heat exchange between the 
fluorescent tube and the outside air is promoted.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to FIG. 1, there is illustrated a cross sectional view of one 
embodiment of fluorescent lamp according to the present invention. A 
cylinder-shaped chassis 10 is made of heat resistant and electrically 
insulating resin material and has a male screw portion 12 at one end 
thereof. The male screw portion 12 is formed substantially cylindrical and 
has a radius smaller than that of chassis 10. The male screw (e.g. E-26 
type) 14 is formed on an outer surface of the male screw portion 12. A 
pair of support arm members 16 and 18 are arranged opposite to each other 
and attached integral to the chassis 10 at the other end thereof. The 
support arm members 16 and 18 extend in the axial direction of the chassis 
10 and serve to fixedly sandwich a reactance ballast 20 therebetween. 
Namely, the ballast 20 has on its opposite sides engaging tongues 22, 
which are bent to engage with recesses 24 of paired support arm members 16 
and 18, respectively, thus causing the ballast 20 to be immovably fixed 
between the support arm members 16 and 18. 
The above-mentioned structure fixing the ballast 20 are housed in a 
bowl-shaped member 26, which is made of heat resistant and electrically 
insulating resin material. An open end 28 of the bowl-shaped member 26 has 
an inner diameter corresponding to the outer diameter of the chassis 10 
and a flange projecting inward and radially. Another open end 30 of the 
bowl-shaped member 26 has an inner diameter larger than at least the outer 
shape of ballast 20. Therefore, the structure in which the ballast 20 is 
fixed is fitted into the bowl-shaped member 26 through the open end 30 and 
foused therein with its male screw portion 12 positioned forward. When the 
structure is housed like this, a stepped portion 32 on the chassis 10 is 
held by the open end 28 of bowl-shaped member 26. When under this 
condition, a screw base 34 made of metal is screwed into the male screw 
portion 12, thus allowing the chassis 10 to be connected, immovable in the 
axial direction, to the open end 28 of the bowl-shaped member 26. 
A partition plate 36 shown in FIG. 2 is attached to the open end 28 of the 
bowl-shaped member 26 by means of a pair of its hooks 38 and 40. The 
partition plate 36 is made of thermally insulating material. The paired 
support arm members 16 and 18 are fitted this time into slots 42 and 44 of 
partition plate 36. When under this condition, the ballast 20 and chassis 
10 are stably housed in the bowl-shaped member 26. 
As shown in FIG. 2, a pair of recesses 46 and 48 are provided in the 
partition plate 36 at opposite sides thereof. Recesses 46 and 48 are 
recessed perpendicular to hooks 38 and 40. The distance between recesses 
46 and 48 of the partition plate 36 is determined depending upon the outer 
shape of the ballast 20. FIG. 3 schematically shows the relative 
positional relation between the partition plate 36 and the bowl-shaped 
member 26 when they are assembled. As shown in FIG. 3, grooves 54 and 56 
are provided in the bowl-shaped member 26 at opposite sides thereof. The 
profile of each of grooves 54 and 56 on the side of open end 30 of the 
bowl-shaped member 26 corresponds to each of paired recesses 46 and 48 in 
the partition plate 36. Axially extending plate portions 58 and 59 (FIG. 
4) of the grooves 54 and 56 are tightly contact with the outer surface of 
the ballast 20 to support the ballast 20. When the partition plate 36 is 
attached to the bowl-shaped member 26, upper ends of the grooves 54 and 56 
of the member 26 closely fitted into the recesses 46 and 48 of the 
partition plate 36, respectively. The support arm portions 16 and 18 are 
also fitted this time into slots 42 and 44 in the partition plate 36. 
Therefore, a chamber in which the ballast 20 is accommodated is 
constituted by the paired support arm members 16 and 18, the plate 
portions 58 and 59 of the grooves 54 and 56 and the partition plate 36. 
A plurality of ventilating slits 60 are arranged extending in the 
circumferential direction of the bowl-shaped member 26, as shown in FIG. 
3. Namely, the ventilating slits 60 extend entirely along the 
circumference of the bowl-shaped member 26 at this portion thereof which 
is adjacent to the screw base 34, but partially along the circumference 
thereof at that portion at which the grooves 54 and 56 extend in the axial 
direction. The reactance ballast 20 housed in the bowl-shaped member 26 
contacts directly with the outside air through the ventilating slits 60. 
Referring again back to FIG. 1, there is shown the cross section of each of 
the ventilating slits 60 in the circumference of the bowl-shaped member 
26. Namely, a ring-shaped wall 62 is erected from the bowl-shaped member 
26 in the axial direction in each of the ventilating slits 60 and has a 
height smaller than or equal to the width of each of the ventilating slits 
60, in this embodiment. Even when the fluorescent lamp is viewed from the 
side thereof, therefore, the ballast 20 and other components such as 
wiring (not shown) housed in the bowl-shaped member 26 are hardly left 
invisible. In addition, these walls 62 serve to prevent dust from easily 
entering into the bowl-shaped member 26 but without lowering its heat 
discharging effect. 
FIG. 4 is a cross sectional view taken along a line IV--IV in FIG. 1. The 
embodiment of fluorescent lamp according to the present invention will be 
further described referring to FIG. 4. A fluorescent tube 64 is attached 
to the partition plate 36, which is attached to the bowl-shaped member 26 
in which the ballast 20 is housed with the screw base 34 fixed projecting 
in the axial direction. The fluorescent tube 64 is bent at at least one 
position thereof so as to be compactly housed in a predetermined closed 
space. In the case of this embodiment, the fluorescent tube 64 is curved 
arc at three positions thereof, so that it has a U-shaped curved tube 
portion 68 at which one ends of reverse U-shaped tube portions 66 and 67 
parallel to each other are connected integral and continuous to each other 
(the shape of fluorescent tube is shown in detail in FIG. 3 of U.S. patent 
application No. 190,252). Electrodes (not shown) are provided at the other 
ends 70 and 71 of reverse U-shaped tube portions 66 and 67, respectively. 
The end electrode portions 70 and 71 adjacent to each other and the lower 
curved tube portion 68 of the fluorescent tube 64 are fixed adjacent to 
one another on the partition plate 36 by means of an attaching member 76, 
which includes holders 78 for holding the end electrode portions 70 and 71 
of the fluorescent tube 64. The attaching member 76 further includes a 
parts support 80 formed integral to the holder for holding the one end 
electrode portion 70 of the fluorescent tube 64, said parts support 80 
serving to support a glow lamp 82, a capacitor 84 and the like and also 
resiliently support the lower U-shaped tube portion 68. The opposite end 
of the parts support 80 is formed like a hook to stably hold the lower 
curved tube portion 68 of the fluorescent tube 64. In other words, the 
fluorescent tube 64 is supported at three points thereof by the attaching 
member 76 and stably fixed together with the glow lamp 82 and capacitor 84 
on the partition plate 36. Under this condition, the end electrode 
portions 70 and 71 and the lower curved tube portion 68 of the fluorescent 
tube 64 are located adjacent to the pair of recesses 46 and 48 of the 
partition plate into which grooves 54 and 56 of bowl-shaped member 26 are 
closely fitted. Therefore, cooling efficiency at the portions 70, 71 and 
68 of fluorescent tube 64 is substantially enhanced because these portions 
70, 71 and 68 are contacted directly with air outside through the grooves 
54 and 56. In addition, the fluorescent tube 64 is separated from the 
ballast 20 in the bowl-shaped member 26 by the partition plate 36. 
Reference numerals 87 and 88 denote upper tops of the reverse U-shaped 
curved tube portions 66 and 67. 
A globe 90 made of known light-transmitting material is fixed to the open 
end 30 of the bowl-shaped member 26 constructed as above. A plurality of 
ring-shaped prism bodies 92 are formed on the outer circumference of the 
globe 90, extending parallel to one another in the circumferential 
direction thereof, for example. Light emitted from the fluorescent tube 64 
is diffused or scattered by the prism bodies 92 and transmitted outside. 
Plural holes 94 are formed at the top portion of the globe 90 so as to 
permit the inner space of the globe 90 to be exposed to the outside. In 
the case of this embodiment, one hole is located at the center top of the 
globe 90 and other ones are selected to be nearest to the tops 87 and 88 
of the reverse U-shaped tube portions 66 and 67 of the fluorescent tube 
64, whereby the upper tops 87 and 88 of the fluorescent tube 64 enclosed 
by the globe 90 are contacted directly with the outside air through these 
holes 94. 
FIG. 5 is a cross sectional view taken along a line V--V in FIG. 4. The 
glow lamp 82 and capacitor 84 are fixed substantially in the center area 
on the partition plate 36 to which the fluorescent tube 64 is stably 
fixed. As more apparent from FIG. 5, the open end of the groove 54 is 
located adjacent to two end electrode portions 70 and 71 of the 
fluorescent tube 64 while the one of the other groove 56 adjacent to the 
lower curved tube portion 68 thereof. 
FIG. 6 shows the above-described fluorescent lamp viewed from the underside 
thereof and the relative positional relation between ventilating slits 60 
formed around the bowl-shaped member 26 becomes more apparent from FIG. 6. 
In the fluorescent lamp having such arrangement as described above 
according to one embodiment of this invention, the reactance ballast 20 is 
housed in the bowl-shaped member 26 in such a way that it is thermally 
isolated or insulated from the curved fluorescent tube 64 by the partition 
plate 36 made of heat resistant material. The ballast 20 contacts 
independently with the outside air through the ventilating slits 60 formed 
in the side of the bowl-shaped member 26. When the lamp is kept turned on, 
therefore, heat radiated from the ballast 20 is not discharge outside 
through the fluorescent tube 64 but directly outside. Namely, the ballast 
20 can be heat-exchanged with air outside through the ventilating slits 60 
and independently of the fluorescent tube 64. 
The bowl-shaped member 26 is further provided with the grooves 54 and 56 
which serve as air-ducts for communicating the inner space of the globe 
90, in which the fluorescent tube 64 is housed, directly with the outside 
air. In addition, the holes 94 are provided at the top portion of the 
globe 90. Therefore, the outside air flows into the inner space of the 
globe 90, in which the fluorescent tube 64 is housed, through the grooves 
54 and 56 and/or the holes 94, thus enabling the ventilation in the globe 
90 to be enhanced. In other words, heat exchange between the fluorescent 
tube 64 in the globe 90 and the outside air is achieved through the 
grooves 54, 56 and/or the holes 94 in the globe 90 independently of that 
of the ballast 20, thus leaving heat exchange between the fluorescent tube 
64 and the outside air uninfluenced by heat radiated from the ballast 20. 
The open ends of the grooves 54 and 56, which serve as air-ducts and which 
are placed to introduce the fresh air from the outside to the inner space 
of the globe 90, are located adjacent to the two end electrode portions 70 
and 71 of the fluorescent tube 64. Therefore, the capacity of air entering 
into the globe 90 through the grooves 54 and 56 and the cooling end 
portions 70 and 71 of the fluorescent tube 64 is so increased as to 
effectively prevent the ambient temperature of the fluorescent tube 64 
from being raised. In addition, the holes 94 formed at the top portion of 
the globe 90 are located adjacent to the upper tops of the reverse 
U-shaped tube portions 66 and 67 of the fluorescent tube 64. Therefore, 
heat discharge effect is enhanced at two upper tops of the tube 64 and 
these tops are locally cooled by the outside air entering through the 
holes 94, so that the fluorescent tube 64 is provided with most cooled 
portions. If the most cooled portions are present partially in the curved 
fluorescent tube 64, the vapor pressure of mercury in the tube 64 is 
determined by the temperature in most cooled portions thereof. Namely, 
even if areas in which temperature is higher than that in the most cooled 
portions are present in the fluorescent tube 64, most of excess mercury 
will be condensed in the most cooled portions of the tube 64 to thereby 
prevent the vapor pressure from being raised in the fluorescent tube 64. 
Therefore, the luminous efficacy of the fluorescent tube 64 can be 
improved as compared with in the conventional one. 
The following table shows a comparison between ratios of luminous flux 
reduction attained by the fluorescent lamp according to the present 
invention and by conventional ones. 
TABLE 
______________________________________ 
Ratio of luminous 
flux reduction (%) 
______________________________________ 
Conventional lamp A about 43 
Conventional lamp B 32 
Lamp according to 12 
the invention 
Lamp according to the 15 
invention without 
ventilating slits (60) 
______________________________________ 
The ratio of luminous flux reduction in the table means a factor of showing 
how all luminous flux of each of actual fluorescent lamps is reduced as 
compared with all luminous flux attained by an ideal fluorescent lamp 
wherein the fluorescent tube is housed in the lamp housing while the 
ballast is experimentally located outside the housing so as to leave the 
fluorescent tube uninfluenced by the ballast. It is apparent that the 
lightening efficiency of lamp becomes better as the ratio of luminous flux 
reduction becomes smaller. "Lamp according to the invention" represents 
the embodiment of fluorescent lamp as described throughout the 
specification and a fluorescent tube of 20 W was employed. "Conventional 
lamp A" represents a fluorescent lamp wherein both of fluorescent tube of 
20 W and ballast are housed in a same space inside the housing. 
"Conventional lamp B" denotes a fluorescent lamp wherein the fluorescent 
tube of 20 W and the ballast and housed in different spaces inside the 
envelope. Four kinds of lamps, including a lamp of this invention with no 
ventilating slits 60, were turned ON with their screw base sides 
vertically down, and all luminous flux in each case was measured when the 
light outputs from the above lamps became stable under the same 
conditions. As apparent from the table, it has been found that the 
fluorescent lamp according to the present invention, even when the 
ventilating slits 60 are not provided, has an extremely lower ratio of all 
luminous flux reduction as compared with conventional ones and that the 
fluorescent lamp according to the present invention allows the fluorescent 
tube to be left almost uninfluenced by heat radiated from the ballast. 
Although the present invention has been shown and described with respect to 
a particular embodiment, various changes and modifications which are 
obvious to a person skilled in the art are deemed to lie within the 
spirit, scope and contemplation of the present invention. The curved 
fluorescent tube is not limited to the one employed in the above-described 
embodiment, but may be simply U-shaped or variously modified. The 
arrangement of housing the ballast is not limited to the one in the 
embodiment but may be variously modified within the scope of the present 
invention.