Electric lamp and discharge devices – With gas or vapor – Having a particular total or partial pressure
Reexamination Certificate
2000-06-08
2003-03-25
Patel, Vip (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having a particular total or partial pressure
C313S635000, C313S639000
Reexamination Certificate
active
06538378
ABSTRACT:
TITLE OF THE INVENTION
Low-pressure Mercury Vapor Discharge Lamp and Ultraviolet-ray Irradiating Apparatus and Method Using the Same
BACKGROUND OF THE INVENTION
The present invention relates to a low-pressure mercury vapor discharge lamp with a relatively high electric power density and a relatively long effective light emission length which is suitable for use in purification, sterilization, disinfection or the like of water by radiation of ultraviolet rays, as well as an ultraviolet-ray irradiating apparatus and method using such a low-pressure mercury vapor discharge lamp.
Ultraviolet rays of a short wavelength range have been used for sterilization, decomposition of toxic organic substances, etc., and low-pressure mercury vapor discharge lamps have heretofore been known as sources for generating ultraviolet rays having a wavelength, for example, of 185 nm or 254 nm. Generally, the low-pressure mercury vapor discharge lamps contain a rare gas, such as argon (Ar) along with a superfluous amount of mercury, and a vapor pressure (vaporization amount) of the mercury varies in response to a temperature of a coldest portion within the discharge lamp. Radiation efficiency of the ultraviolet rays is closely related with the mercury vapor pressure; for example, the 254 nm ultraviolet rays present a highest radiation efficiency at a vapor pressure of about 6×10
−3
torr and at a 40° C. temperature. At 70° C., the vapor pressure of the ultraviolet rays rises to about 5×10
−2
torr, and the radiation efficiency decreases by more than 20%. For this reason, the low-pressure mercury vapor discharge lamp is normally designed such that the temperature during operation is held at and around 40° C. In recent years, attempts have been made to increase the density of electrical energy input to the discharge lamp (lamp input density) for an enhanced processing capability of the discharge lamp; in this case, the operating temperature would exceed 40° C., so that there has been employed an approach of enclosing the mercury in an amalgam state. This approach comprises alloying the mercury with another metal, such as bismuth (Bi), tin (Sn) or indium (In) and placing the resultant alloy within the discharge lamp to thereby suppress the mercury vapor pressure during high-temperature operation. Exemplary comparison between a vapor pressure curve of an indium-bismuth amalgam and a vapor pressure curve of mercury (pure mercury) is given in FIG.
5
.
FIG. 4
shows an example of a conventional low-pressure mercury vapor discharge lamp. Here, reference numeral
1
represents a light-emitting tube bulb formed of quartz glass, which has opposite ends hermetically closed by glass stems
2
a
and
2
b
. Reference numeral
4
represents an indium-bismuth amalgam fixed on the glass stem
2
a
. Reference numerals
21
a
and
21
b
represent a pair of filaments, which are each coated with a barium-oxide (BaO)-based thermoelectronic substance in order to permit a smooth electric discharge. These filaments
21
a
and
21
b
are retained on the respective glass stems
2
a
and
2
b
, and are electrically connected, via lead wires
22
a
,
22
b
and
22
c
,
22
d
, to terminals
31
a
,
31
b
and
31
c
,
31
d
, respectively, of metallic caps or bases
3
a
and
3
b
. In the light-emitting tube bulb
1
, there is also contained an appropriate amount of argon (Ar) gas. Once the low-pressure mercury vapor discharge lamp is turned on by being connected to a predetermined power supply, electric discharge is produced between the filaments
21
a
and
21
b
, so that the mercury vapor is increased by a heat resulting from the electric discharge (discharge heat) and the vaporized mercury atoms are excited to emit ultraviolet rays.
Although the mercury vapor discharge lamp containing an amalgam has a great advantage of ensuring a high ultraviolet-ray radiation efficiency by suppressing the mercury vapor pressure during high-temperature operation, it would present significant inconveniences or disadvantages due to the fact that the mercury vapor pressure is suppressed not only during the high-temperature operation but also in low-temperature conditions prior to the turning-on or lighting-up of the lamp. One of such inconveniences is that the discharge lamp can not be readily activated because a high voltage is required to start the electric discharge. Normally, the temperature within the light-emitting tube bulb prior to the lighting-up is substantially equal to a temperature of an atmosphere in which the lamp is placed. For example, in a situation where the temperature of the atmosphere is 20° C., there exists a mercury vapor pressure of about 1.2×10
−3
torr in a discharge lamp containing a normal form of mercury (pure mercury), and the necessary discharge-starting voltage can be lowered greatly by the Penning effect produced by the mercury vapor pressure and argon gas, so that the electric discharge can be initiated smoothly. By contrast, in a discharge lamp containing an amalgam, the mercury vapor pressure prior to the lighting-up is suppressed below 1/10 of that in the above-mentioned mercury-containing discharge lamp, which would lessen the Penning effect and hence raise the necessary discharge-starting voltage level. Thus, activating the amalgam-containing discharge lamp would require a higher discharge-starting voltage than required for activation of the traditional-type discharge lamp.
Another inconvenience presented by the amalgam-containing discharge lamp is a slow rise in the light amount of the emitted ultraviolet rays. It is considered that a primary cause of such a slow rise in the light amount is a synergism of several factors, such as: insufficient emission of ultraviolet rays immediately after the lighting-up due to an inherently small amount of mercury vapor within the discharge lamp; an insufficient lamp input immediately after the lighting-up because of the small mercury vapor amount; a hard-to-warm tendency of the discharge lamp due to an insufficient discharge heat resulting from the insufficient lamp input immediately after the lighting-up; and even slower evaporation of the mercury from the amalgam due to the hard-to-warm tendency of the discharge lamp.
Even in the discharge lamp containing the mercury in an amalgam state, these inconveniences would not lead to practical problems as long as the lamp's effective light emission length (which equals a length between the filaments) is relatively short. Because, the discharge lamps with a short effective light emission length can be activated with a relatively low discharge-starting voltage and can be filled with mercury vapor at a rapid speed. Further, in the discharge lamp with a low lamp input density, presence of the above-mentioned inconveniences is not even considered to be problematic, because there is no absolute necessity to contain the mercury in an amalgam state. However, the above-mentioned inconveniences would become serious problems with such an elongated, high-density discharge lamp that is often required in the field of purification processing by ultraviolet rays. Namely, in recent years, there has been an increasing demand for further enhanced processing capabilities in the field of the purification processing based on use of ultraviolet rays, and therefore a discharge lamp with a longer effective light emission length as well as a higher lamp input density has become necessary for an increased processing capacity. In such a discharge lamp with a longer effective light emission length, the above-mentioned inconveniences would become significant problems to be properly overcome since the necessary discharge-starting voltage has to increase as the effective light emission length increases and the increased effective light emission length results in a greater time lag until the mercury vapor fills the entire interior of the discharge lamp. As an example of such a discharge lamp, there is currently being used a high-density discharge lamp with a lamp input density exceeding about 1 W/cm. With this type of
Morrison & Foerster / LLP
Patel Vip
Photoscience Japan Corporation
Williams Joseph
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