Electric lamp and discharge devices – With gas or vapor – Having electrode lead-in or electrode support sealed to...
Reexamination Certificate
1998-09-15
2001-06-05
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode lead-in or electrode support sealed to...
C313S632000, C313S113000
Reexamination Certificate
active
06242861
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to direct current discharge lamps and, more particularly, to improvements in a direct current discharge lamp for use in an optical instrument and to an improved light source using such lamp as attached to a reflector.
2. Description of the Related Art
Discharge lamps such as extra-high pressure mercury lamps and metal halide lamps are widely used in optical instruments such as liquid crystal projectors, OHPs and motion picture projectors and in general lightings. Such discharge lamps are highly advantageous in that their energy efficiency is three to five times higher than that of incandescent lamps such as halogen lamps, which emit light by heating filament, and their life time is five to ten times longer than that of such incandescent lamps.
Recently, demands have arisen from users, particularly from users of optical instruments that discharge lamps be further improved in life time, energy efficiency (specifically, to achieve a higher screen brightness per electric power applied to lamps) and evenness of screen brightness.
Intensive study and development have been made to improve discharge lamps for use in optical instruments so as to satisfy such demands; for example, enabling lamps to use direct current in order to enhance their emission efficiency in optical instruments, shortening the spacing between opposite electrodes to shorten the arc length or increasing the pressure in the lamps thereby improving the luminance of arc, and improving the reflecting efficiency of a reflector based on an improved arc luminance.
FIG. 4
shows a conventional discharge lamp (B). This conventional lamp (B) involves the following problems: (1) anode
12
b
, which is heated to a higher temperature than cathode
12
a
in DC lighting, is subjected to severe damage and loss, resulting in a substantial luminous flux attenuation from the initial period of use, hence in an unsatisfactory life time (refer to FIG.
5
); (2) seal-cut portion
27
of bulb
21
a
interfere with the light path to cause a 10 to 20% loss in lighting efficiency (refer to Table 1); (3) the seal-cut portion
27
is reflected on a screen as shadow causing uneven screen brightness (refer to Table 2); and like problems.
To solve the problems (2) and (3) of the above problems, study has made to develop tipless lamps which are fabricated without using any sealing tube so as to avoid formation of any seal-cut portion as indicated at
27
. Such tipless lamps are now being realized for a lower wattage.
Such tipless technique, however, involves not a few problems remaining unsolved. The first one is unfeasibility of obtaining lamps of a higher wattage due to process limitations. Specifically, a higher wattage lamp requires the use of a glass tube having a thicker wall and a larger diameter and this makes it difficult to achieve tipless sealing. The second one is incapability of preventing malfunction of a lamp due to impurities produced in the lamp. Specifically, in the manufacturing process of even a lower wattage lamp, certain amounts of impurities are produced from a glass tube used. The amounts of impurities grow larger as the wattage of a lamp grow higher because such a higher wattage lamps employs a larger glass tube. Larger amounts of impurities remaining in the lamp cause malfunction of the lamps. The third one is costly manufacture, which leads to expensive optical instruments such as a projector. Moreover, the problem (1) is left unsolved.
It is, therefore, an object of the present invention to provide a direct current discharge lamp having a prolonged life time.
Another object of the present invention is to provide a direct current discharge lamp enjoying an improved energy efficiency.
Yet another object of the present invention is to provide a direct current discharge lamp providing improved evenness in screen brightness.
Further object of the present invention is to provide a direct current discharge lamp of a higher wattage and to enable the manufacturing cost of a direct current discharge lamp to be reduced.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a direct current discharge lamp comprising a bulb portion containing therein an anode and a cathode, a first seal portion outwardly extending from the bulb portion on the anode side, a second seal portion outwardly extending from the bulb portion on the cathode side, a pair of feeder elements respectively inserted through the first and second seal portions for feeding electricity to the anode and cathode, and a extended tube portion interconnecting the bulb portion and the first seal portion.
With a conventional direct current discharge lamp, when the lamp is turned on, arc is produced between the anode and the cathode and electrons are emitted from the cathode toward the anode. This heats the anode to a high temperature with the result that the anode material is evaporated and scattered within the bulb portion to cause darkening of the bulb portion.
With the direct current discharge lamp of the above construction according to the present invention, in contrast, the provision of the extended tube portion which serves to extend the space adjacent the based portion of the anode allows the heat of the anode to dissipate easily. This suppresses the evaporation of the anode material from the anode, hence the darkening of the bulb portion. As a result, luminous flux attenuation is mitigated to prolong the lamp life time.
Preferably, the anode is extended from the bulb portion into the extended tube portion. This feature enables the anode to be lengthened relative to a conventional one. Such a lengthened anode has an increased heat capacity and allows easier heat dissipation thereby suppressing excessive heating of the anode. This advantage results in the lamp enjoying a further prolonged life time.
In a preferred embodiment the extended tube portion is formed with a seal-cut portion. Usually such a seal-cut portion is formed on the bulb portion as a trace of introducing filler substances (gases or the like) into the bulb portion and hence interferes with light passing therethrough. However, the advantageous feature according to the present invention that the seal-cut portion is located on the extended tube portion allows light from the luminous spot appearing adjacent the leading end of the cathode and from a region immediately next to the luminous spot to advance outwardly of the lamp without interference of the seal-cut portion. Thus, a screen when illuminated by such lamp is free of any shadow attributable to the seal-cut portion, resulting in a more even screen brightness.
The present invention also provides a light source comprising a reflector and a direct current discharge lamp, the lamp comprising a bulb portion containing therein an anode and a cathode, a first seal portion outwardly extending from the bulb portion on the anode side, a second seal portion outwardly extending from the bulb portion on the cathode side, a pair of feeder elements respectively inserted through the first and second seal portions for feeding electricity to the anode and cathode, and an extended tube portion interconnecting the bulb portion and the first seal portion and formed with a seal-cut portion, the first seal portion of the lamp being inserted into a central mounting hole of the reflector.
With this construction, the seal-cut portion is located adjacent the central mounting hole of the reflector, and even if light passing through the seal-cut portion is reflected by the reflector, such light does not pass through a liquid crystal panel or aperture of an optical instrument which restricts light adapted to illuminate the screen. Thus, any shadow caused by the seal-cut portion is not formed on the screen.
The foregoing and other objects, features and attendant advantages of the present invention will become apparent from the following detailed description of the preferred embodiments of the invention when read in conjunction with the accompanying drawings, in w
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Nimeshkumar D.
Phoenix Electric Co. Ltd.
Williams Joseph
LandOfFree
Direct current discharge lamp and light source having the... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Direct current discharge lamp and light source having the..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Direct current discharge lamp and light source having the... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2444517