JPH07153371A - Electrodeless high intensity discharge lamp - Google Patents

Abstract

(57) [Abstract] [Objective] In an electrodeless high intensity discharge lamp containing at least one metal iodide as a filling component, the iodine level in the lamp is controlled to stabilize the arc and improve the lamp performance. Provide an iodine getter. [Structure] Using silver as an iodine getter, silver is added in a predetermined amount to a filling material of an electrodeless high-luminance metal halide discharge lamp. Silver reacts with liberated iodine to form silver iodide, which has a relatively high boiling point and a relatively low vapor pressure, so that iodine levels promote and maintain arc stability. Controlled to a level below the arc instability threshold. Furthermore, silver does not corrode the walls of the quartz arc tube, nor does it accelerate the decomposition of iodide in the lamp fill, and thus does not increase the devitrification and corrosion of the quartz walls. Thus, the use of silver as the iodine getter improves lamp performance and life.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-intensity metal halide discharge lamp, and more specifically, by using silver in the metal halide discharge lamp, the iodine level in the metal halide discharge lamp is controlled to stabilize the arc. And improving lamp performance.

[0002]

In the operation of high intensity metal halide discharge lamps, visible light is emitted by the metal portion of the metal halide fill at a relatively high pressure during excitation, which is typically caused by the application of electrical current. One class of high intensity metal halide lamps is the electrodeless lamp, which sets a solenoidal electric field in a high pressure gas fill consisting of a combination of one or more metal halides and an inert buffer gas. By doing so, arc discharge is generated. In particular, a lamp fill, or discharge plasma, is excited by supplying a radio frequency (RF) current to an excitation coil surrounding an arc tube containing the fill. The arc tube and excitation coil assembly essentially acts as a transformer coupling the RF energy into the plasma. That is,
The excitation coil acts as a primary coil, and the plasma functions as a one-turn (turn) secondary coil. The RF current in the excitation coil produces a time-varying magnetic field and also creates an electric field in the plasma. This electric field is completely closed by itself, that is, a solenoidal electric field. Current flows as a result of this electric field, causing a toroidal arc discharge in the arc tube.

A typical electrodeless metal halide discharge lamp uses a metal halide that produces white light for general lighting. Unfortunately, however, the electrodeless high intensity metal halide discharge lamps produce free iodine after exposure to the plasma arc discharge and devitrify the arc tube wall. The amount of free iodine in the arc tube increases with time. When this accumulated iodine exceeds a threshold value, arc instability occurs, and as a result, the arc disappears.

Therefore, it is desirable to provide an iodine getter that controls the level of iodine in an electrodeless high intensity metal halide discharge lamp to improve arc stability. Such iodine getters must be viable to extend the useful life of the lamp and not increase devitrification and corrosion of the arc tube wall.

[0005]

SUMMARY OF THE INVENTION Silver is added to the fill of discharge lamps to control the vapor level of iodine in electrodeless high intensity metallihalide discharge lamps containing at least one metal iodide as the fill component. Silver reacts with free iodine to form silver iodide (Ag I). This silver iodide has a relatively high boiling point and a relatively low vapor pressure. The iodine level is controlled below the arc instability threshold to stabilize and maintain the arc. Furthermore, silver does not corrode the walls of quartz arc tubes. This is because silica (Si O ₂ ) is much more stable than silver oxide (Ag ₂ O). Furthermore, even if silver is added to the arc tube, sodium iodide (Na I) and cerium iodide (Ce
I ₃ ), lanthanum iodide (La I ₃ ), and neodymium iodide (Nd I ₃ ) do not accelerate the decomposition of iodide in the fill. Without the addition of silver, iodide decomposition increases devitrification and corrosion of the quartz wall. Therefore, lamp performance and life is improved by using silver as the iodine getter.

The features and advantages of the present invention will become apparent upon a reading of the following detailed description of the invention in conjunction with the accompanying drawings.

[0007]

DETAILED DESCRIPTION FIG. 1 illustrates a typical electrodeless high intensity metal halide discharge lamp 10. As shown, the lamp 10 has an arc tube 14 made of heat resistant glass such as fused silica. As an example, arc tube 14 is illustrated as having a generally elliptical shape. However, other shapes of arc tube may be desirable for some applications. For example, the arc tube 14 may be spherical, or in the form of a short cylinder or "pillbox" with optionally rounded edges.

The arc tube 14 includes at least one metal halo.
Contains a filling containing genide, in which a solenoid
Arc discharge is excited during lamp operation. Appropriate filling
The object is at least one rare earth metal halide (eg
For example, cerium iodide (Ce I ₃), Lanthanum iodide (L
a I₃), Neodymium iodide (Nd I₃), Iodine iodide
Ojim (Pr I₃)) And at least one alkali
Metal halides (eg sodium iodide (Na
I), cesium iodide (Cs I), lithium iodide (L
i I)). One typical packing is white
Emits visible light with high efficiency and good color rendering
Sodium iodide, yo combined in a weight ratio
Cerium iodide and xenon. Such packing
Are described in U.S. Pat. No. 4,810,938.
Another typical packing is US Pat. No. 4,972,120.
Lanthanum iodide, sodium iodide as described in
A combination of um, cerium iodide and xenon
It

Power is supplied to the lamp 10 by an excitation coil 16 provided around the arc tube 14 and the excitation coil 16 is driven by an RF signal through a ballast 18. A suitable excitation coil 16 is, for example, US Pat.
2 having a structure as described in No. 39,903
It is a wound coil. Such a coil structure is very efficient and has minimal interference with the light from the lamp. The overall shape of the excitation coil described in US Pat. No. 5,039,903 is such that a trapezoid with opposite sides is located around a coil centerline that lies in the same plane as the trapezoid but does not intersect the trapezoid. It has a surface shape formed by rotating. However, US Pat. No. 4,812,702
Other suitable coil structures, such as those described in No. 1, may be used. In particular, the one described in U.S. Pat. No. 4,812,702 is a six-turn coil configured to have a generally V-shaped cross section on either side of the coil centerline. Yet another suitable excitation coil may be, for example, solenoid shaped.

In operation, as a result of the RF current supplied to the coil 16, a time-varying magnetic field is generated which creates an electric field within the arc tube 14 which is itself completely closed. As a result of this solenoidal electric field, a current flows through the filling in the arc tube 14 and a toroidal arc discharge 20 is generated in the arc tube 14. The operation of a typical electrodeless high intensity discharge lamp is described in the aforementioned US Pat. No. 4,810,938.

In the present invention, silver is added to the fill of an electrodeless high intensity discharge lamp to control the vapor level of iodine in the electrodeless high intensity discharge lamp and stabilize the arc. During operation, silver reacts with iodine liberated by metal loss at the arc tube wall to form silver iodide (Ag I).
Under lamp operating conditions, silver iodide evaporates and some remains in the liquid state. The vapor pressure of silver iodide is determined by its liquid temperature, which is controlled by the power applied to the system. Iodine bound to silver in the liquid state is not released to the vapor state. The reason for this is that silver iodide has a relatively high boiling point (1506 ° C) and a relatively low vapor pressure. Therefore, the total iodine concentration in the vapor state is adjusted only by the liquid temperature, and the accumulation of excess iodine is avoided. Therefore, the vapor pressure of iodine is controlled to a level lower than the threshold of arc instability, and the stability of the arc is promoted and maintained.

The amount of silver used as the iodine getter according to the present invention for controlling the vapor pressure of iodine below the threshold of arc instability depends on the type and amount of filler components, the size of the arc tube. And shape, excitation power and operating temperature. Typical amounts are, for example, in the range of about 0.4 to 4 milligrams. Advantageously, silver does not corrode (or reduce) the walls of a quartz arc tube. This is because silica (Si 0 ₂ ) is much more stable than silver oxide (Ag ₂ O). Further, silver may be, for example, sodium iodide (Na I), cerium iodide (Ce I ₃ ), lanthanum iodide (La I ₃ ), neodymium iodide (Nd I ₃ ), or praseodymium iodide (Pr I ₃ ). Addition of silver to the arc tube does not accelerate iodide decomposition as it is less stable than such iodide lamp fills. Decomposition of iodide increases devitrification and corrosion of the quartz wall. Therefore, lamp performance and life are improved by using silver as the iodine getter.

EXAMPLES The performance of the two Group A and B lamps was compared. Each group consisted of a lamp using silver as the iodine getter and a corresponding reference lamp without the iodine getter.
The lamps of groups A and B have a size of 19 mm x 2
It is a 6 mm elliptical shape. 5: 1 for each lamp in group A
8 mg of a mixed filler composed of sodium iodide (Na I) and neodymium iodide (Nd I ₃ ) in a molar ratio of Each lamp in Group B had a 7: 1 molar ratio of sodium iodide (Na I) and neodymium iodide (Nd I).
10 mg of the mixed filling consisting of ₃ ) was added. 1 mg of silver was added to the lamps according to the invention of group A and 0.4% to the lamps according to the invention of group B.
9 mg of silver was added. Group A lamp is 31m
m lamps were operated with an inner diameter excitation coil, group B lamps were operated with a 34 mm inner diameter excitation coil, and each group was tested at a coil power level of 300 watts. Each of the lamps of groups A and B has a quartz envelope filled with nitrogen gas so as to surround the arc tube, the outside diameter of the envelope of group A is 30 mm, and the outside diameter of the envelope of group B is It was 33 mm.

Photometric data of the lamps of group A were taken at operating times of 100 hours, 500 hours, 1000 hours and 2000 hours. The graph in FIG. 2 compares the efficiency of lamps using silver as the Group A iodine getter with the corresponding reference lamps. Lamp efficiency was higher for lamps using silver as the iodine getter than for reference lamps. Moreover, the lumen loss during the first 2000 hours of operation was much less with the lamp using silver as the iodine getter (2.5%) than with the reference lamp (15%).

The free iodine generated in the arc tube is
It was measured by absorption spectroscopy at a wavelength of 5 nm. The results for lamps using silver as the iodine getters of groups A and B and their corresponding reference lamps are shown graphically in FIGS. 3 and 4, respectively. In the reference lamp without getter, iodine accumulated rapidly. In contrast, the lamp using silver as the iodine getter according to the invention had a very low level of free iodine. As shown in FIG. 4, the reference lamps of Group B had no arc at 2642 hours when the iodine absorbance was 0.36 (which is equivalent to 0.56 mg of I ₂ formed in the lamp). It was observed to become stable. At the same operating time, the arc was stable and the iodine absorbance was near zero for the lamp with the silver getter.

Beneficially, the addition of silver to the fill component also improved the color temperature and color consistency of the Group A and B lamps. FIG. 5 shows the color temperature as a function of lamp operating time for a lamp with a silver getter of group A and a reference lamp of group A. The reference lamp has a color temperature of 400 in 2000 hours.
There was an increase in ° C, but a constant color temperature was observed for the lamp with the silver getter.

FIG. 6 shows a comparison of the color rendering index (CRI) measured for lamps with Group A silver getters and reference lamps. CRI values measured at 100 hours were almost the same for both the lamp with the silver getter and the reference lamp. As the operating time of the lamp increased, the CRI value of the reference lamp increased and the CRI of the lamp with the silver getter remained almost constant. Therefore, color consistency was improved by adding silver to the fill.

It was also observed that in lamps of Groups A and B, the addition of silver to the lamps did not increase the deterioration of the arc tube wall. While the preferred embodiment of the invention has been illustrated and described, it will be clear that such embodiment is merely an example. Many modifications, variations and substitutions will be possible to those skilled in the art without departing from the invention. Accordingly, the invention is defined by the claims.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional side view of a typical electrodeless high intensity metal halide discharge lamp.

FIG. 2 is a graph showing the efficiency of a group of electrodeless high intensity metal halide discharge lamps using silver as the iodine getter compared to corresponding lamps without the getter.

FIG. 3 shows iodine absorption of a group of electrodeless high-luminance metal halide discharge lamps using silver as an iodine getter,
3 is a graph showing a comparison with a corresponding lamp not using the getter.

FIG. 4 is a graph showing the iodine absorption of another group of electrodeless high intensity metal halide discharge lamps using silver as the iodine getter compared to corresponding lamps without the getter.

FIG. 5 is a graph showing the color temperature of a group of electrodeless high intensity metal halide discharge lamps using silver as the iodine getter compared to corresponding lamps without the getter.

FIG. 6 is a graph showing the color rendering index of a group of electrodeless high intensity metal halide discharge lamps using silver as the iodine getter compared to corresponding lamps without the getter.

[Explanation of symbols]

 10 Electrodeless high-luminance metal halide discharge lamp 14 Arc tube 16 Excitation coil 18 Ballast 20 Arc discharge

Claims (6)

[Claims] 1. A light-transmissive arc tube that internally generates a plasma arc discharge, a filler that is placed in the arc tube and contains at least one metal iodide, and is provided around the arc tube. An excitation coil for exciting the arc discharge in the filling, and an iodine getter configured of silver added to the filling in a predetermined amount to control the vapor level of iodine during lamp operation for stabilizing the arc. An electrodeless high-luminance discharge lamp having: 2. The at least one metal iodide is
Cerium iodide (Ce I ₃ ), lanthanum iodide (La I
₃ ), neodymium iodide (Nd I ₃ ), praseodymium iodide (Pr I ₃ ), and a combination thereof, which is selected from the group of rare earth metal iodides. lamp. 3. The at least one metal iodide is
Sodium iodide (Na I), cesium iodide (Cs
The electrodeless high intensity discharge lamp of claim 1 which is selected from the group of alkali metal iodides consisting of I), lithium iodide (Li I), and combinations thereof. 4. The electrodeless high intensity discharge lamp according to claim 1, wherein the filling contains at least one rare earth metal halide and at least one alkali metal halide. 5. The at least one rare earth metal halide comprises neodymium iodide (Nd I ₃ ) and the at least one alkali metal iodide comprises sodium iodide (Na I). Electrodeless high brightness discharge lamp. 6. The electrodeless high intensity discharge lamp of claim 1, wherein the predetermined amount is in the range of about 0.4 to 4 milligrams.