Electric lamp and discharge devices – With gas or vapor – Having specified electrode spacing
Reexamination Certificate
1998-10-09
2003-04-08
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having specified electrode spacing
C313S639000
Reexamination Certificate
active
06545413
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a metal halide lamp, and more particularly to a metal halide lamp utilized for a projection display such as a liquid crystal projection display, and for a luminance mainly incorporated into a reflector and the like.
(2) Description of the Prior Art
Liquid crystal projection systems have been gaining popularity as a display means for magnifying and projecting characters or graphics on the screen.
This type of apparatus typically has such a construction that a light from a light source lamp is projected into a liquid crystal panel via a reflector and subsequently the light is projected onto a screen via a focusing optical system, which is a projecting optical system. Having such a construction, this type of apparatus can utilize only the light emitted from a limited region adjacent to the focal point of the reflector. It is therefore desirable that, in a lamp for the light source, the light emission by arc be concentrated in as small an area as possible. The reason is that the. efficiency in utilizing light increases as the light emitting area becomes smaller, thus achieving high illuminance at the screen. This tendency becomes more apparent as reduction of the physical sizes of reflectors and the like advances in the attempts to reduce the size, weight, and cost of the projection devices.
It is also desirable that the lamp used for the light source of projection systems have well-balanced light emission throughout the whole visible range of spectrum. In other words, if the lamp exhibits well-balanced light emission in each red, green, and blue region of spectrum, the projection system employing the lamp will be thereby able to reproduce, for example, an image of healthy human's complexion as it should be. However, if the light emission in the red region is insufficient, the displayed image of the healthy human's complexion turns out to be bluish, thus pale and unhealthy.
In consideration of the above, metal halide lamps, ultra high-pressure mercury lamps, or the like have been used for conventional liquid crystal projection displays and the like.
Metal halide lamps are a high-pressure discharge lamp characterized in that various types of metal halides are contained in high-pressure mercury vapor. One type of such a lamp is disclosed on pp. 18-24 of
Characteristics and Theoretical Analysis of Metal Halide Lamps
, T. Higashi, The Journal of the Illuminating Engineering Institute of Japan, Vol. 73, No. 9, 1989. The lamp includes the iodides of Sc (scandium) and Na (sodium) in the fill material, and exhibits a high luminous efficacy of 90 lm/W. (It is to be understood that the term ‘luminous efficacy’ herein means a luminous flux per unit input electric power to a lamp.) The reason for this is considered to be that a complex iodide possibly Na
2
ScI
5
), which has a higher vapor pressure than that of Sc and Na as a simple body, is formed from Sc and Na therein. (See pp. 209-214 of
Complex Halide Vapors in Metal Halide Type HID Lamps
, C. Hirayama et al., The Journal of the Illuminating Engineering Society, July 1977). The special distribution of this lamp is shown in FIG.
7
. As seen from
FIG. 7
, a large number of bright-line spectrums are observed in the visible range, which indicates that the lamp has relatively high color rendering properties.
In the process of completing the invention, the present inventors experimentally produced a metal halide lamp having a construction described below and shown in FIG.
8
. The lamp has an arc tube
101
, composed of a light-transmissive quartz vessel having an approximately spherical shape, an inner diameter of 10.8 mm, and an inner capacity of 0.7 cc. Each of the opposite ends of the arc tube
101
is sealed at a seal portion
106
. A pair of tungsten electrodes
102
is provided within the arc tube
101
. Each of the tungsten electrodes
102
is connected to an external lead
104
via a molybdenum foil
103
. A tungsten coil
105
is also connected to each of the tungsten electrodes
102
by welding. The gap between the terminal ends of the electrodes
102
(the distance between the electrodes) is set at 2.2 mm. A fill material
107
is enclosed in the arc tube
101
. The fill material
107
comprises 0.6 mg of InI (indium iodide), 1 mg of TmI
3
(thulium iodide), argon with 0.2 atm at a room temperature, and 49 mg of mercury.
The luminous efficacy of the lamp according to the above-described construction was about 80 lm/W when the lamp was disposed horizontally and operated at a rated input power. The luminous flux that reaches a 40-inch screen was measured under the condition where the light emitted from the lamp is projected with a taking angle of 7 degrees via an ellipsoidal reflector. The size of the luminous flux per unit input power was 4 lm/W. The size of the luminous flux per unit power measured according to the above-described manner is hereinafter referred to as ‘projection efficiency’. It is to be noted here that conventional well known metal halide lamps have a longer distance between the electrodes (for example, approx. 3 mm), and therefore exhibit even lower projection efficiency than the above-described lamp. As to the spectral distribution, the lamp exhibited abundant light emission over the whole visible range, as shown in FIG.
9
. In particular, the light emission in the red region of spectrum was more abundant than that of the previously-mentioned metal halide lamp comprising iodides of Sc and Na, which leads to more favorable color reproduction properties when the lamp is used for projecting image and the like.
An ultra high-pressure mercury lamp, for example, as the one described in Japanese Unexamined Patent Publication No. 2-148561, generally has such a construction that mercury is primarily included in the fill material and the vapor pressure of the mercury becomes very high during the operation. Halides of other metals are not included therein. An ultra high-pressure mercury lamp of this type exhibited a luminous efficacy of about 60 lm/W and a projection efficiency of 11 lm/W, when operated at a rated power. The spectral distribution of this lamp is shown in FIG.
10
. Since this type of ultra high-pressure mercury lamp is operated with high vapor pressure, the light emission in the red region of spectrum, the wavelength range of around 600 to 650 nm, is a little improved over other types of mercury lamps which is operated with lower vapor pressure. Nonetheless, the amount of light emission in the red region of around 600 to 650 nm is still obviously smaller than that of the metal halide lamps mentioned above.
Now, the drawbacks of these prior art lamps will be further detailed below.
Although the above-described experimental metal halide lamp has relatively high luminous efficacy, it has a drawback in that the lamp cannot achieve high projection efficiency. This is due to the difficulty of making the light emitting area smaller. In consideration of this, as an index to indicate the size of the light emitting area, are diameters were measured for those lamps. From the results, it was confirmed that the experimental metal halide lamp containing In had a larger arc diameter of 1.1 mm than the ultra high-pressure mercury lamp, whose arc diameter was 0.7 mm. The metal halide lamp containing Na too has a drawback of larger arc diameter than the ultra high-pressure mercury lamp. Hence, these lamps cannot attain sufficient brightness at the screen in case where the lamps have a small reflector or a small to angle for the projection lens in the projecting optical system The reason for a large arc diameter in these lamps is that alkali metals such as Na and the like have low ionization potential as a simple body, for example, a ionization potential of Na being 5.14 eV, therefore easily ionize even in the low-temperature, peripheral area of the arc in the lamps. The alkali metals therefore generate free electrons, resulting in a wide electric current path, i.e., resulting in a large arc diameter. This is detailed on p.220 of
Horiuchi Makoto
Takahashi Kiyoshi
Takeda Mamoru
Clove Thelma Sheree
Parkhurst & Wendel LLP
LandOfFree
Metal halide lamp does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Metal halide lamp, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Metal halide lamp will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3075746