Title: Fluorescent lamp and high intensity discharge lamp with improved luminous efficiency
Abstract: The present invention improves the luminous efficiency of lamps that emit light due to electric discharge, such as a fluorescent lamp and an HID lamp. The fluorescent lamp includes a glass tube used as a fluorescent tube made of a glass material containing an emissive element. When exposed to ultraviolet light (with the peak wavelength of 251 nm) emitted due to mercury excitation, the emissive element emits ultraviolet light having a longer wavelength than that. The HID lamp includes an envelop made of a glass material that contains an emissive element. When exposed to ultraviolet light emitted due to excitation of an emissive material enclosed in an arc tube, the emissive element emits ultraviolet light having a longer wavelength than that.
Patent Number: 6,906,475 Issued on 06/14/2005 to Atagi
| Inventors:
|
Atagi; Tomoko (Takatsuki, JP)
|
| Assignee:
|
Matsushita Electric Industrial Co., Ltd. (Osaka-Fu, JP)
|
| Appl. No.:
|
897230 |
| Filed:
|
July 2, 2001 |
Foreign Application Priority Data
| Jul 07, 2000[JP] | 2000-206487 |
| Current U.S. Class: |
315/246; 313/485; 315/291 |
| Intern'l Class: |
H05B 041/16; H01J001/62 |
| Field of Search: |
315/291,246,344,248,358,326,DIG.2
313/485,487,489,636,493,496,110,112
|
References Cited [Referenced By]
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| 3617357 | Nov., 1971 | Nagy.
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| 3670194 | Jun., 1972 | Thornton, Jr. et al.
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| 3707641 | Dec., 1972 | Thornton.
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| 4001628 | Jan., 1977 | Ryan.
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| 4038203 | Jul., 1977 | Takahashi.
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| 4079288 | Mar., 1978 | Maloney et al.
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| 4356428 | Oct., 1982 | Hanlet.
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| 5118985 | Jun., 1992 | Patton et al.
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| 5464462 | Nov., 1995 | Langer et al.
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| 5528107 | Jun., 1996 | Marlor et al.
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| 5552665 | Sep., 1996 | Trushell.
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| 5602444 | Feb., 1997 | Jansma.
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| 5604396 | Feb., 1997 | Watanabe et al.
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| 5666031 | Sep., 1997 | Jennato et al.
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| 5726528 | Mar., 1998 | Jansma et al.
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| 5801483 | Sep., 1998 | Watanabe et al.
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| 5869927 | Feb., 1999 | Matsuo et al.
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| 5961883 | Oct., 1999 | Yamazaki et al.
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| 6018216 | Jan., 2000 | McIntosh.
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| 6348763 | Feb., 2002 | Collins.
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| 6583566 | Jun., 2003 | Jin et al.
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| Foreign Patent Documents |
| 31 28 649 | Feb., 1983 | DE.
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| 921554 | Jun., 1999 | EP.
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| 0921 554 | Jun., 1999 | EP.
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| 2167 428 | May., 1986 | GB.
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| 49-99610 | Sep., 1974 | JP.
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| 52-142710 | Nov., 1977 | JP.
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| 6-196127 | Jul., 1994 | JP.
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| 8-325031 | Dec., 1996 | JP.
| |
| 10167755 | Jun., 1998 | JP.
| |
| 11167899 | Jun., 1999 | JP.
| |
Primary Examiner: Wong; Don
Assistant Examiner: Tran; Chuc
Claims
1. A fluorescent lamp comprising:
a fluorescent tube that is composed of a glass tube having a phosphor layer formed
on an inner surface thereof and mercury and a rare gas enclosed therein; and
electrodes that cause an electrical discharge within the fluorescent tube,
wherein the glass tube is made of a glass material that contains an emissive
element mixed within the glass material, the emissive element emitting, when exposed
to first ultraviolet light that is emitted due to mercury excitation, second ultraviolet
light that has a longer wavelength than the first ultraviolet light.
2. The fluorescent lamp of claim 1,
wherein the emissive element emits visible light together with the second ultraviolet
light, when exposed to the first ultraviolet light.
3. The fluorescent lamp of claim 1,
wherein an entire luminous flux emitted from the fluorescent lamp includes:
a first luminous flux that is formed by visible light emitted from the phosphor
layer when exposed to the first ultraviolet light;
a second luminous flux that is formed by visible light emitted from the emissive
element when exposed to the first ultraviolet light; and
a third luminous flux that is formed by visible light emitted from the phosphor
layer when exposed to the second ultraviolet light,
wherein the second luminous flux and the third luminous flux together constitute
at least 2% of the entire luminous flux emitted from the fluorescent lamp.
4. The fluorescent lamp of claim 1,
wherein a thickness of the glass tube is 0.62 mm or less.
5. The fluorescent lamp of claim 1,
wherein a thickness of the phosphor layer is below 20 μm.
6. A fluorescent lamp comprising:
a fluorescent tube that is composed of a glass tube having a phosphor layer formed
on an inner surface thereof and mercury and a rare gas enclosed therein; and
electrodes that cause an electrical discharge within the fluorescent tube,
wherein the glass tube is made of a glass material containing an oxide mixed
within the glass material, the oxide including at least one element selected from
the group consisting of titanium, zirconium, vanadium, niobium, tantalum, molybdenum,
tungsten, thallium, stannum, plumbum, bismuth, lanthanum, cerium, praseodymium,
neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,
thulium, ytterbium, and lutetium.
7. The fluorescent lamp of claim 6, wherein
the glass material contains 0.01 wt % to 10 wt % of an oxide of at least one
element selected from the group consisting of titanium, zirconium, vanadium, niobium,
tantalum, molybdenum, tungsten, lanthanum, cerium, praseodymium, neodymium, samarium,
europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium,
and lutetium.
8. The fluorescent lamp of claim 6, wherein
the glass material contains 0.01 wt % to 0.5 wt % of an oxide of at least one
element selected from the group consisting of thallium, stannum, plumbum, and bismuth.
9. A fluorescent lamp comprising:
a fluorescent tube having a protective layer formed on an inner surface thereof,
a phosphor layer formed on the protective layer, and mercury and a rare gas enclosed
therein; and
electrodes that cause an electrical discharge within the fluorescent tube,
wherein the protective layer contains an oxide of at least one emissive element
selected from the group consisting of zirconium, vanadium, niobium, tantalum, molybdenum,
tungsten, thallium, stannum, plumbum, bismuth, praseodymium, neodymium, samarium,
gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.
10. The fluorescent lamp of claim 9,
wherein an entire luminous flux emitted from the fluorescent lamp includes:
a first luminous flux that is formed by visible light emitted from the phosphor
layer when exposed to the first ultraviolet light;
a second luminous flux that is formed by visible light emitted from the emissive
element when exposed to the first ultraviolet light; and
a third luminous flux that is formed by visible light emitted from the phosphor
layer when exposed to the second ultraviolet light,
wherein the second luminous flux and the third luminous flux together constitute
at least 2% of the entire luminous flux emitted from the fluorescent lamp.
11. The fluorescent lamp of claim 9, wherein
the protective layer contains 0.01 wt % to 10 wt % of an oxide of at least one
element selected from the group consisting of zirconium, vanadium, niobium, tantalum,
molybdenum, tungsten, praseodymium, neodymium, samarium, gadolinium, dysprosium,
holmium, erbium, thulium, ytterbium, and lutetium.
12. The fluorescent lamp of claim 9,
wherein an entire luminous flux emitted from the fluorescent lamp includes:
a first luminous flux that is formed by visible light emitted from the phosphor
layer when exposed to ultraviolet light that is emitted due to mercury excitation;
a second luminous flux that is formed by visible light emitted from an emissive
element contained in the protective layer when exposed to ultraviolet light that
is emitted due to mercury excitation; and
a third luminous flux that is formed by visible light emitted from the phosphor
layer when exposed to ultraviolet light that is emitted from the emissive element
when exposed to ultraviolet light that is emitted due to mercury excitation, and
wherein the second luminous flux and the third luminous flux together constitute
at least 2% of the entire luminous flux emitted from the fluorescent lamp.
13. A high intensity discharge lamp comprising:
an arc tube in which an emissive material is enclosed, the emissive material
emitting visible light and ultraviolet light when excited by an electric discharge;
and
an envelop whose one surface surrounding the arc tube is covered with a phosphor
layer,
wherein the envelop is made of a glass material that contains an emissive protective
layer, the emissive protective layer emitting, when exposed to first ultraviolet
light that is emitted due to excitation of the emissive material by the electric
discharge, second ultraviolet light that has a longer wavelength than the first
ultraviolet light.
14. The high intensity discharge lamp of claim 13,
wherein the emissive protective layer emits visible light together with the second
ultraviolet light when exposed to the first ultraviolet light.
15. The high intensity discharge lamp of claim 13,
wherein an entire luminous flux emitted from the high intensity discharge lamp
includes:
a first luminous flux that is formed by the visible light emitted due to the
excitation of the emissive material by the electric discharge;
a second luminous flux that is formed by visible light emitted from the emissive
protective layer when exposed to the first ultraviolet light; and
a third luminous flux that is formed by visible light emitted from the phosphor
layer when exposed to the second ultraviolet light.
16. A high intensity discharge lamp comprising:
an arc tube in which an emissive material is enclosed, the emissive material
emitting visible light and ultraviolet light when excited by an electric discharge;
and an envelop whose one surface surrounding the arc tube is covered with a phosphor
layer,
wherein the envelop is made of a glass material that contains an oxide mixed
within the glass material, the oxide including at least one element selected from
the group consisting of titanium, zirconium, vanadium, niobium, tantalum, molybdenum,
tungsten, thallium, stannum, plumbum, bismuth, lanthanum, cerium, praseodymium,
neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,
thulium, ytterbium, and lutetium.
17. A high intensity discharge lamp comprising:
an arc tube in which an emissive material is enclosed, the emissive material
emitting visible light and ultraviolet light when excited by an electric discharge;
and
an envelop that is provided so as to envelop the arc tube,
wherein the envelop is made of a glass material that contains an emissive protective
layer, the emissive protective layer emitting visible light, when exposed to ultraviolet
light that is emitted due to excitation of the emissive material by the electric
discharge.
18. The high intensity discharge lamp of claim 17,
wherein an entire luminous flux emitted from the high intensity discharge lamp
includes:
a first luminous flux that is formed by the visible light emitted due to the
excitation of the emissive material by the electric discharge; and
a second luminous flux that is formed by visible light emitted from the emissive
protective layer when exposed to the ultraviolet light that is emitted due to the
excitation of the emissive material by the electric discharge.
19. A high intensity discharge lamp comprising:
an arc tube in which an emissive material is enclosed, the emissive material
emitting visible light and ultraviolet light when excited by an electric discharge;
and
an envelop that is provided so as to envelop the arc tube,
wherein the envelop is made of a glass material that contains an oxide mixed
within the glass material, the oxide including at least one element selected from
the group consisting of titanium, zirconium, vanadium, niobium, tantalum, molybdenum,
tungsten, thallium, stannum, plumbum, bismuth, lanthanum, cerium, praseodymium,
neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium,
thulium, ytterbium, and lutetium.
20. A fluorescent lamp comprising:
a fluorescent tube having a protective layer formed on an inner surface thereof,
a phosphor layer formed on the protective layer, and mercury and a rare gas enclosed
therein; and
electrodes that cause an electrical discharge within the fluorescent tube,
wherein the protective layer contains an oxide of at least one element selected
from the group consisting of titanium, zirconium, vanadium, niobium, tantalum,
molybdenum, tungsten, thallium, stannum, plumbum, bismuth, praseodymium, neodymium,
samarium, gadolinium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium,
wherein the protective layer contains 0.01 wt % to 0.5 wt % of an oxide of at
least one element selected from the group consisting thallium, stannum, plumbum,
and bismuth.
21. A fluorescent lamp comprising:
a fluorescent glass tube;
a phosphor layer formed on an inner surface of the glass tube;
mercury enclosed within the glass tube;
a gas enclosed within the glass tube having a characteristic of enabling the
mercury excitation for emitting a first ultraviolet light when excited by an electrical
discharge, the first ultraviolet light exciting the phosphor layer to emit a first
visible luminous flux for transmission through the fluorescent glass tube;
electrodes within the fluorescent glass tube for causing the electrical discharge;
and
an emissive protective layer embedded within the fluorescent glass tube having
a characteristic of emitting a second visible luminous flux within the fluorescent
glass tube when activated by the first ultraviolet light, while permitting transmission
of at least a portion of the first visible luminous flux and the second visible
luminous flux to an exterior of the fluorescent glass tube.
22. The fluorescent lamp of claim 21, wherein the emissive protective layer further
has a characteristic of emitting a second ultraviolet light when activated by the
first ultraviolet light, the second ultraviolet light activates the phosphor light
to emit a third visible luminous flux to the exterior of the fluorescent glass tube.
23. The fluorescent lamp of claim 22, wherein the emissive protective layer includes
an oxide of at least one element selected from the group consisting of titanium,
zirconium, vanadium, niobium, tantalum, molybdenum, tungsten, thallium, stannum,
plumbum, bismuth, lanthanum, cerium, praseodymium, neodymium, samarium, europium,
gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.
Description
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a fluorescent lamp and a high intensity discharge lamp.
(2) Related Art
Fluorescent lamps and high intensity discharge (HID) lamps are widely
known to emit light with high efficiency.
A fluorescent lamp includes an arc tube in which mercury and a rare gas are enclosed.
The inner surface of the arc tube is coated with phosphors. The electric discharge
performed in the arc tube excites mercury to emit ultraviolet light with the dominant
wavelength of 254 nm. The ultraviolet light excites the phosphors to emit visible
light. In this way, a luminous flux can be obtained. Typical fluorescent lamps
of this type have conventionally been straight tube type fluorescent lamps and
circular fluorescent lamps, with bulb-type fluorescent lamps and compact fluorescent
lamps being widely introduced in recent years.
An HID lamp is the generic name for a high-pressure mercury lamp, a metal halide
lamp, and a high-pressure sodium lamp.
The high-pressure mercury lamp emits light due to the electric discharge under
mercury vapor of 100 to 100 kPa.
The metal halide lamp emits light as follows. With the electric discharge, metal
halide is dissociated into metallic atoms and halide atoms. The metallic atoms
are then excited to emit visible light.
The high-pressure sodium lamp emits light due to the electric discharge under
sodium vapor.
As basic performances of these fluorescent lamps and HID lamps, obtaining a larger
luminous flux with lower electric power consumption and achieving a long lifetime
are pursued. Active research and development have been made for accomplishing these
basic performances.
As one example, Japanese Laid-Open Patent Application No. H11-167899 discloses
a technique for lengthening a lifetime of a fluorescent lamp. According to the
disclosure, the luminous intensity of a conventional fluorescent lamp employing
soda glass is likely to decrease because sodium is eluted from the soda glass at
the time the fluorescent lamp is manufactured or lit, and the eluted sodium reacts
with mercury. In view of this, the fluorescent lamp according to the technique
employs such glass from which sodium is less likely to be eluted than the conventional
soda glass, for preventing the luminous intensity from decreasing.
Also, to obtain a larger luminous flux of a fluorescent lamp with lower electric
power consumption, for example, research and development have been made to improve
luminance of phosphors, and to secure a long arc length by making an arc tube thinner.
These research and development have contributed to improving the performances
of fluorescent lamps and HID lamps to some extent. However, there are increasing
demands for further improving these performances in recent years. To meet these
demands, techniques for further decreasing the electric power consumption and providing
larger luminous flux are called for.
SUMMARY OF THE INVENTION
The present invention aims to improve the luminous efficiency of lamps that emit
light due to the electric discharge, such as a fluorescent lamp and an HID lamp.
In view of the above object, the fluorescent lamp of the present invention includes,
as a fluorescent tube, a glass tube made of a glass material containing an emissive
element. When exposed to the ultraviolet light (with the peak wavelength of 254
nm) emitted by mercury excitation, the emissive element emits ultraviolet light
with a longer wavelength.
Alternatively, the fluorescent lamp of the present invention includes
a glass tube whose inner surface is covered with a protective layer containing
the above mentioned emissive element. On the protective layer made of metallic
oxide as its base material, a phosphor layer is formed.
According to the fluorescent lamp of the present invention, the electric
discharge under mercury vapor in the fluorescent tube produces ultraviolet light
with the peak wavelength of 254 nm. This ultraviolet light illuminates the emissive
element to emit long wave ultraviolet light, and visible light. This long wave
ultraviolet light excites the phosphor layer to emit secondary visible light. With
this effect, the utilization efficiency of the ultraviolet light emitted by mercury
excitation for the luminous flux of the fluorescent lamp is improved. As a result
of this, the total amount of the luminous flux can be increased by at least 2%,
compared to a conventional lamp without the emissive element. To improve the visible
light transmission rate of the glass tube or the protective layer, it is preferable
to melt the emissive element into a glass material that forms the glass tube, or
into metallic oxide that is the base material of the protective layer.
Also, the HID lamp of the present invention includes an envelop made of a glass
material containing the above mentioned emissive element. When exposed to the ultraviolet
light emitted by excitation of an emissive material enclosed inside an arc tube,
the emissive element is excited to emit ultraviolet light with a longer wavelength.
As the emissive elements to be contained in the glass for use in the fluorescent
lamp and in the HID lamp, it is preferable to use oxides of the below listed elements.
The elements are:
- Ti, Zr, V, Nb, Ta, Mo, W, Tl, Sn, Pb, Bi, La, Ce, Pr, Nd, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, and Lu.
The present invention can also be applied to an incandescent lamp. In the incandescent
lamp, a bulb is made to contain an emissive element selected from the above, so
that the utilization efficiency of light emitted due to the electric discharge,
for the luminous flux of the incandescent lamp can be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects, advantages and features of the invention will become
apparent from the following description thereof taken in conjunction with the accompanying
drawings that illustrate a specific embodiment of the invention. In the drawings:
FIG. 1 shows an appearance of a compact fluorescent lamp relating to a first
embodiment of the present invention;
FIG. 2 shows a cross-sectional view of a glass tube constituting a fluorescent
tube of the fluorescent lamp;
FIG. 3 is for explaining a light emitting mechanism of the fluorescent lamp;
FIG. 4 shows a measurement method of an emission spectrum in Experiment 2;
FIG. 5 shows the emission spectrum resulting from Experiment 2;
FIG. 6 is a characteristic graph showing the relation between glass plate thickness
and visible light transmission rate, resulting from Experiment 3;
FIG. 7 is a characteristic graph showing the relation between glass tube thickness
and relative luminous intensity;
FIG. 8 is a characteristic graph showing the relation between phosphor layer
thickness and relative luminous intensity;
FIG. 9 shows a cross-sectional view of an arc tube of a fluorescent lamp relating
to a second embodiment of the present invention;
FIG. 10 shows a mercury fluorescent lamp relating to a third embodiment of the
present invention;
FIG. 11A shows a metal halide lamp relating to the third embodiment of the present
invention; and
FIG. 11B shows a high-pressure sodium lamp relating to the third embodiment
of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[First Embodiment]
FIG. 1 shows an appearance of a compact fluorescent lamp to which the first
embodiment of the present invention relates. The compact fluorescent lamp is constructed
by a fluorescent tube
10 fixed to a base
20. The fluorescent tube
10 is made up of six straight glass tubes (glass bulbs)
11.
The neighboring glass tubes
11 are bridge-connected so that the six glass
tubes
11 are connected with one another to form a single discharge space
therein. A rare gas such as argon, and mercury are enclosed inside the discharge
space. Also, the fluorescent tube
10 is provided with electrodes (not illustrated)
at both ends of the discharge space.
Inside the base
20 is provided an ignition circuit (not illustrated)
for igniting the fluorescent tube
10.
FIG. 2 shows a cross-sectional view of a glass tube
11 constituting the
fluorescent tube
10.
The glass tube
11 is made of soda glass. To be noted is that the soda
glass contains an element that is excited to emit light with wavelengths ranging
from ultraviolet to visible regions when exposed to ultraviolet light with the
wavelength of 254 nm (such an element is hereinafter referred to as an "emissive element").
Examples of emissive elements are oxides of: elements in the groups
4A,
5A, and
6A; elements in the groups
3B,
4B, and
5B;
and elements in lanthanoide series.
Specific examples of the elements in the groups
4A,
5A, and
6A are titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), tantalum
(Ta), molybdenum (Mo), and tungsten (W).
Specific examples of the elements in the groups
3B,
4B, and
5B are thallium (Tl), stannum (Sn), plumbum (Pb), and bismuth (Bi).
Specific examples of the elements in lanthanoide series are lanthanum (La),
cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium
(Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium
(Yb), and lutetium (Lu).
To form the glass tube
11, a powdered oxide of at least one element selected
from the above listed elements is mixed with a soda glass material before melting
the soda glass material. This mixed powder is subjected to a melting process and
then to a forming process.
The phosphor layer
12 is formed by applying three-band phosphors to the
inner surface of the glass tube
11.
Note that a preferable range of the thickness of the glass tube
11 and
the phosphor layer
12 will be explained later in this specification.
(Effects)
FIG. 3 is for explaining a light emitting mechanism of the above fluorescent lamp.
The fluorescent lamp in the present embodiment produces a luminous flux substantially
based on the same mechanism as that of conventional fluorescent lamps. In detail,
the ignition circuit applies pressure to the electrodes provided in the fluorescent
tube
10, causing electric discharge in the discharge space formed within
the fluorescent tube
10. This electric discharge excites mercury and a rare
gas enclosed in the discharge space, to produce ultraviolet light "UV
1"
(with the dominant wavelength of 254 nm). The ultraviolet light "UV
1" illuminates
the phosphor layer
12, exciting the phosphors to produce visible light "V
1"
(with a wavelength of approximately 400 nm or more). The visible light "V
1"
is transmitted through the glass tube
11, forming a chief luminous flux
from the fluorescent tube
10.
In addition to this chief luminous flux, the fluorescent lamp of the present
invention
also emits secondary luminous fluxes (visible light "V
2" and visible light
"V
3") in the following way.
The ultraviolet light "UV
1" produced in the fluorescent tube
10
is partially transmitted through the phosphor layer
12 and illuminates the
glass tube
11. Here, the glass tube
11 contains an emissive element
as explained before. The emissive element is excited with the transmitted portion
of the ultraviolet light "UV
1" to emit near-ultraviolet light "UV
2"
(with a wavelength longer than 254 nm), and visible light "UV
2" from the
glass tube
11.
Furthermore, the near-ultraviolet light "UV
2" emitted from the
glass tube
11 partially illuminates the phosphor layer
12. This portion
of the near ultraviolet light "UV
2" excites the phosphors constituting the
phosphor layer
12 to emit visible light "V
3".
Note here that the emissive element hardly absorbs visible light, and is being
uniformly melted in glass that forms the glass tube
11. Accordingly, the
emissive element cannot be an obstacle for visible light to be transmitted through
the glass tube
11. Therefore, the visible light "V
1", "V
2",
and "V
3" are transmitted through the glass tube
11 mostly without
being attenuated, to form the luminous flux of the fluorescent lamp.
As described above, the fluorescent lamp in the present invention has the improved
luminous efficiency because it produces not only the chief luminous flux (visible
light "V
1") but also the secondary luminous fluxes (visible light "V
2"
and "V
3") due to the emissive element contained in the glass tube
11.
Also, the glass tube
11 is made of soda glass in which the emissive
element is being melted. This is more effective compared to when the glass tube
is made of quartz glass in which the emissive element is being melted because the
emissive element combined with the soda glass works more effectively to convert
ultraviolet light with a wavelength of around 254 nm into long wave ultraviolet
light or into visible light.
Here, the concentration of the emissive element to be contained in the glass
tube
11 can be considered as follows. If the concentration is too low, the
emissive element emits only a small amount of light. On the other hand, if the
concentration is too high, the emissive element absorbs ultraviolet light due to
its self-absorption property. Taking this balance into account, the concentration
of the emissive element should preferably be set in such a range that realizes
high luminous efficiency.
Also, the preferable range of the concentration varies depending on the type
of the emissive element. For the oxides of the elements in the groups
4A,
5A, and
6A and the elements in lanthanoide series, the concentration
should preferably be set in the range of 0.01 to 10 wt % inclusive. For the oxides
of the elements in the groups
3B,
4B, and
5B, the concentration
should preferably be set in the range of 0.01 to 0.5wt % inclusive.
As indicated by the experimental results which will be described later, a proper
amount of emissive element contained in the glass tube
11 enables secondary
luminous fluxes (visible light V2 and V
3) to be produced at the ratio of
2% or more relative to the total luminous fluxes (visible light V
1, V
2,
and V
3).
Note here that the oxides of the elements listed above each have a unique emission
spectrum, and differ in various conditions such as its accessibility.
For example, the oxides of the elements in lanthanoide series mostly have emission
spectrums with a number of relatively sharp peak wavelengths. The peak wavelengths
of the emission spectrums range widely from ultraviolet to visible regions.
On the other hand, the oxides of the elements in the groups
3B,
4B,
and
5B have emission spectrums with broad peak wavelengths ranging from
300 to 400 nm. Particularly, thallium oxide (TlO) has high luminous intensity.
Taking these various conditions into account, oxides of one or more suitable
elements can be selected from the above listed elements and used as emissive elements
when determining the composition of the glass for use as the fluorescent tube.
This wide selection of the emissive elements is advantageous because it allows
the glass composition of the fluorescent tube to be tailored for its purposes.
In view of improving the luminous efficiency, the oxides of the elements in lanthanoide
series, more particularly, oxides of Gd and Tb are suitable for use.
This is because the oxides of these elements have such emission spectrums that
are suitable for efficiently exciting fluorescent lamp phosphors.
To be more specific, when a phosphor layer of a fluorescent lamp is illuminated
with ultraviolet light, the conversion efficiency of the ultraviolet light into
visible light depends on the wavelength of the ultraviolet light. The oxides of
these elements emit larger amounts of light having wavelengths in the range of
260 to 400 nm in their emission spectrums. This range is where the conversion efficiency
of ultraviolet light exciting general fluorescent lamp phosphors into visible light
is favorably high.
Also, the oxides of these elements emit larger amounts of light having wavelengths
of around 550 nm, where the sensibility of the human eye is high. Because of this,
these emissive elements are considered suitable for improving the luminous efficiency.
(Experiment 1)
| TABLE 1 |
| |
| Sample No. |
1 |
2 |
3 |
4 |
5 |
6 |
| |
| |
| Composition |
TIO (wt %) |
0 |
0.001 |
0.01 |
0.1 |
0.3 |
0.5 |
| Character- |
Initial Luminous |
2300 |
2300 |
2350 |
2450 |
2480 |
2500 |
| istics |
Flux Value (100 h), |
| |
1 m |
| |
Luminous Flux |
75.5 |
75.6 |
76 |
75.8 |
75.5 |
76 |
| |
Maintenance Factor |
| |
(4000 h), % |
| |
Sample No. 1 shown in Table 1 above is a compact fluorescent lamp relating
to a comparative example. Samples No. 2 to No. 6 are compact fluorescent lamps
relating to the present embodiment.
There fluorescent lamps used in the experiment each are 145 mm in overall length,
with the glass tube diameter of 12.5 mm, and with rated voltage of 32 W.
The fluorescent lamps No. 2 to No. 6 relating to the present embodiment each
include the glass tube
11 made of soda glass composed of SiO
2
68 wt %, Al
2O
3 1.5 wt %, Na
2O 5wt %, K
2O
7 wt %, MgO 5 wt %, CaO 4.5 wt %, SrO 5 wt %, BaO 6 wt %, and Li
2O 1
wt %. Note here that TlO was added to this soda glass as an emissive element. The
concentration of TlO in the glass tube
11 was set at various values (0.001,
0.01, 0.1, 0.3, and 0.5 wt %) as shown in Table 1.
The phosphor layer
12 was formed by three-band phosphors with the color
temperature of 5000K.
The fluorescent lamp No. 1 relating to the comparative experiment has the same
construction as the fluorescent lamps relating to the present embodiment except
that TlO was not added to the glass tube.
The initial luminous flux value and the luminous flux maintenance factor of these
fluorescent lamps relating to the comparative experiment and the present embodiment
were measured according to the following measurement method.
Measurement Method:
The initial luminous flux value (100 h, 1 m) is a value obtained by measuring
a luminous flux of each fluorescent lamp after a life test of 100 hours.
The luminous flux maintenance factor is a ratio of a luminous flux of each fluorescent
lamp measured after a life test of 4000 hours (repeating a 45 minute illumination/15
minutes off cycle) to the above obtained initial luminous flux value.
Measurement Results and Considerations:
The measurement results are shown in Table 1.
Comparing the initial luminous flux values shown in Table 1, the initial
luminous flux value of sample No. 2 which contains only 0.001 wt % of TlO is the
same as that of sample No. 1 which does not contain TlO. However, the initial luminous
flux values of samples No. 3 to No. 6 which respectively contain 0.01 to 0.5 wt
% of TlO are higher than that of sample No. 1 by at least 2%. Looking at the luminous
maintenance factors of these samples, on the other hand, only subtle differences
can be observed.
From this experiment, it can be found that a proper amount of emissive element
contained in a glass tube can improve the initial luminous flux value of the fluorescent
lamp by at least 2%, without decreasing the luminous flux maintenance factor. It
can also be found that it is preferable to set the TlO concentration in the glass
tube at 0.01 wt % or more.
(Experiment 2)
The emission spectrum of the soda glass which contains 0.3 wt % of TlO used for
sample No. 5 relating to the present embodiment and the emission spectrum of the
soda glass used for sample No. 1 relating to the comparative example, when exposed
to ultraviolet light with the wavelength of 254 nm, were measured according to
the following measurement method.
Measurement Method:
A test piece of each soda glass with the thickness of 2 mm and each side length
of 20 mm was prepared. As shown in FIG. 4, each test piece
31 was illuminated
with excitation light
32 having the wavelength of 254 nm with the incident
radiation intensity of 0.4 mW/cm
2. The emission spectrum from the test
piece
31 was measured using an instantaneous spectroscope
33.
Measurement Results and Considerations:
The measurement results are shown in FIG.
5. In the figure, each mark
⋄ indicates the measurement result of sample No. 1, and each mark □
indicates the measurement result of sample No. 5.
As can be seen from the measurement results shown in FIG. 5, sample No. 1 which
does not contain TlO emits little light having wavelengths longer than 254 nm,
whereas sample NO. 5 which contains 0.3 wt % of TlO emits light having broad wavelengths
ranging from 315 nm as its peak to a visible region of around 450 nm.
As explained using FIG. 3 above, the following can be proved by these measurement
results. By illuminating glass containing TlO with ultraviolet light "UV
1"
having the peak wavelength of 254 nm, excited ultraviolet light "UV
2" and
excited visible light "UV
2" are produced.
Note that although TlO was used as the emissive element in Experiments 1 and
2, experiments where the other oxides of the elements listed above were used as
emissive elements were also conducted. In these experiments, the similar results
as Experiments 1 and 2 were obtained.
Also, the optimum range of the concentration of each element to be contained
was examined and determined as follows. For the oxides of the elements in the groups
4A,
5A, and
6A and the elements in lanthanoide series, the
optimum range is 0.01 to 10 wt %. For the oxides of the elements in the groups
3B,
4B, and
5B, the optimum range is 0.01 to 0.5 wt %.
(Experiment 3) Experiment and Considerations for Glass Thickness
The experiment was conducted to examine the visible light transmission rate of
soda glass plates which each contain 0.3 wt % of emissive element (TlO) but each
vary in the thickness.
FIG. 6 shows a characteristic graph showing the results of this experiment.
From the figure, it can be found that the transmission rate decreases as the thickness
of the glass plate increases.
Also, the relative luminous intensity of glass tubes each composed of a glass
material containing 0.3 wt % of TlO with the fixed diameter of 12.5 mm, but each
with the thickness being made varied was examined.
FIG. 7 shows a characteristic graph written based on the results of this experiment.
In the figure, marks ◯ indicate the measured relative luminous intensity
when the thickness of the glass tube is set relatively at 1, 2, and 3 mm. In the
graph, the curve indicates the relation between the thickness of the glass tube
and the relative luminous intensity estimated based on these measured values. From
the figure, it can be found that the relative luminous intensity decreases as the
thickness of the glass tube increases when the thickness of the glass tube is relatively
small, that is, 1.5 mm or less.
To sum up, making the glass tube containing an emissive element thinner, both
the transmission rate and the relative luminous intensity can be improved. In view
of this, for increasing the relative luminous intensity of the fluorescent lamp
relating to the present embodiment, the thickness of the glass tube
11 is
to be set smaller.
Known from these experiments are as follows. While glass tubes with the thickness
of above 0.62 mm are used as arc tubes for conventional general fluorescent lamps,
it is advantageous for the fluorescent lamp relating to the present embodiment
to set the thickness of the glass tube
11 at 0.62 mm or less.
(Experiment 4) Experiment and Considerations Regarding Phosphor Layer Thickness
The relative luminous intensity of a fluorescent lamp employing glass which contains
0.3 wt % of an emissive element (TlO) and the relative luminous intensity of a
fluorescent lamp employing conventional soda glass which does not contain the emissive
element were measured, in the case where the thickness of the phosphor layer in
each fluorescent lamp is made varied in the range of 0 to 40 μm.
FIG. 8 shows a characteristic graph showing the relation between the thickness
of the phosphor layer and the relative luminous intensity.
In FIG. 8, the relative luminous intensity of the fluorescent lamp employing
the
general soda glass is the highest when the thickness of the phosphor layer is above
20 μm, whereas the relative luminous intensity of the fluorescent lamp employing
the soda glass containing TlO is the highest when the thickness of the phosphor
layer is below 20 μm.
The following can be found from the experimental results. While it is advantageous
for general fluorescent lamps to set the thickness of the phosphor layer at 20
μm or more, it is advantageous for the fluorescent lamp relating to the present
embodiment to set the thickness of the phosphor layer below 20 μm for increasing
the luminous intensity.
[Second Embodiment]
FIG. 9 shows a cross-sectional view of the arc tube of the fluorescent lamp
relating to the present embodiment.
The fluorescent lamp relating to the present embodiment has the same construction
as the fluorescent lamp relating to the first embodiment of the present embodiment,
with the only difference being in a fluorescent tube
40 employed instead
of the fluorescent tube
10. In the fluorescent tube
40, a protective
layer
43 is formed between a fluorescent layer
42 and a glass tube
41.
The protective layer
43 is a transparent layer that contains metallic
oxide selected form the group consisting of zinc oxide (ZnO), titanium oxide (TiO
2),
silicon oxide (SiO
2), and aluminum oxide (Al
2O
3)
as a base material, and additionally contains an emissive element in a state of
being melted in the base material.
Specific examples of emissive elements are oxides of elements (Ti, Zr, .
. . ) listed in the first embodiment. Among these, the oxides of the elements in
lanthanoide series, more particularly, oxides of Gd and Tb, are especially suitable
for use in this case.
Note that the phosphor layer
42 is the same as the phosphor layer
12
in the first embodiment.
Note also that the glass tube
41 does not contain an emissive element.
The protective layer
43 is formed in the following way.
A powder material of an emissive element is mixed with a powder material of a
metallic
oxide that is a base material of the protective layer
43, and this mixed
powder is melted and ground to form a mixed powder compound. This mixed powder
compound is then added to a solvent such as an organic solvent (isopropyl alcohol)
together with a dispersing agent, so that it is dispersed in the solvent. In this
way, a coating liquid is prepared. This coating liquid is then applied to the inner
surface of the gas tube
41 with a spray method or the like, dried, and baked,
to form the protective layer
43.
By melting the emissive element into the base material of the protective layer
43 as described above, an oxide compound composed of metallic oxide (ZnO,
TiO
2, SiO
2, or Al
2O
3) of the base material
and metallic oxide of the emissive element is formed.
For applying the mixed powder to the inner surface of the glass tube
41,
not only the wet method employed above but also an electrostatic spraying method,
or a sol-gel method using a liquid obtained by dissolving alkoxide into an organic
solvent may be employed.
As described above, the protective layer
43 which contains the emissive
element can produce both the effect to improve the luminous flux maintenance factor
due to the base material contained therein, and the effect to improve the luminous
efficiency due to the emissive element contained therein.
The base material in the protective layer
43 makes it difficult for sodium
to be diffused from the glass so as to be transmitted to the phosphor layer
12.
Therefore, the protective layer
43 also produces the effect to increase
the luminous flux maintenance factor, by preventing blackening which occurs in
the phosphor layer
12 due to mercury reacting with sodium in the glass.
Furthermore, the emissive element produces the effect to improve the luminous efficiency.
As in the first embodiment, the improvement here is made not only in the luminous
flux formed by visible light emitted due to ultraviolet light with the wavelength
of 254 nm exciting the phosphors in the phosphor layer
42. Besides, the
emissive element contained in the protective layer
43 emits light that forms
other luminous fluxes, resulting in the luminous efficiency being improved.
To be more specific, ultraviolet light emitted due to the electric discharge
within
the fluorescent tube
40 is partially transmitted through the phosphor layer
42. The transmitted portion of the ultraviolet light illuminates the protective
layer
43, exciting the emissive element contained in the protective layer
43. The excited emissive element emits near-ultraviolet light and visible
light from the protective layer
43. Furthermore, the ultraviolet light emitted
from the protective layer partially illuminates the phosphor layer
42. This
portion of the ultraviolet light excites the phosphors in the phosphor layer
42
to emit visible light.
Also, since the emissive element is melted in the base material of the protective
layer
43, the emissive element does never be an obstacle for the visible
light to be transmitted through the protective layer.
Note that the effects of the emissive element to emit near-ultraviolet light
and visible light can be produced because the emissive element is melted in the
base material to form oxide compounds as described above. These effects are considered
impossible when metallic oxide of the base material and metallic oxide of the emissive
element are simply mixed in the form of particles.
The optimum range of the concentration of the emissive element in the protective
layer
43 is the same as in the first embodiment. The optimum range for the
oxides of the elements in the groups
4A,
5A, and
6A and the
elements in lanthanoide series is 0.01 to 10 wt %, whereas the optimum range for
the elements in the groups
3B,
4B, and
5B is 0.01 to 0.5 wt %.
The thickness of the protective layer
43 is preferably be set in the range
of 1 to 30 μm.
Note that the present embodiment describes the case where the glass tube
41
does not contain the emissive element. However, as a modified example, the emissive
element may be contained in both the protective layer
43 and the glass tube
41.
Also, an element such as TiO
2 has both the mercury transmission
preventing effect and excitation emission effect, and therefore, a single use of
TiO
2 might seem to produce the same effects produced by the present
embodiment. However, with the single use of such an element, the excitation emission
effect dramatically decreases due to a self-absorption property of the element.
Furthermore, such single use of the element limits a method to form the protective
layer because it limits material types that can be used to form the protective
layer. On the contrary, with the combined use of the base material and the emissive
element, the self-absorption of the emissive element can be reduced. Furthermore,
in this case, many combinations of material types of the base material and material
types of the emissive element are available. When determining the composition of
the protective layer, the present invention is advantageous because it provides
the wide selection of materials and of methods for forming the protective layer.
As a preferable combination, silicon oxide or aluminum oxide as the base material
and gadolinium oxide and/or terbium oxide as the emissive element can be considered.
[Third Embodiment]
The present embodiment described the case where the present invention is applied
to HID lamps, taking a fluorescent mercury lamp, a metal halide lamp, and a high-pressure
sodium lamp for example.
FIG. 10 shows an example of the fluorescent mercury lamp.
The fluorescent mercury lamp is one type of a high-pressure mercury lamp, and
is roughly composed of an arc tube
51, a base
52, and an envelop
53 as shown in the figure.
The arc tube
51 is made of transparent quartz glass, and is equipped with
electrodes
54 at both ends. Inside the arc tube
51 are enclosed mercury
and argon.
The envelop
53 is composed of a glass tube
55 provided so as to
envelop the arc tube
51. The inner surface of the glass tube
55 is
covered with the phosphor layer
56.
In the arc tube
51, the electric discharge under high pressure mercury
vapor of 100 to 1000 kPa causes emission of visible light. Besides the visible
light, ultraviolet light is emitted in the arc tube
51. The ultraviolet
light illuminates the phosphor layer
56 in the envelop
53, exciting
emission of visible light.
Here, the glass tube
55 of the envelop
53 is made of borosilicate
glass in which at least one emissive element selected from the emissive elements
mentioned in the first embodiment (oxides of Ti, Zr . . . ) is melted.
With this construction, the envelop
53 produces the same effects as the
fluorescent tube
10 described in FIG. 3 in the first embodiment. More specifically,
ultraviolet light emitted from the arc tube
51 is partially transmitted
through the phosphor layer
56, and illuminates the glass tube
55.
The emissive element contained in the glass tube
55 is excited by the transmitted
portion of the ultraviolet light, emitting long wave ultraviolet light, and visible
light. The ultraviolet light emitted form the glass tube
55 illuminates
the phosphor layer
56, exciting emission of visible light.
With this effect, the fluorescent mercury lamp in the present embodiment is
provided with the improved luminous efficiency compared to the case when the emissive
element is not added to the glass tube.
Also, in the present embodiment, the emissive element is included not in the
arc tube
51 made of quartz glass, but
