GB2054261A - Metal halide high-intensity discharge lamps - Google Patents

Abstract

Metal halide lamp with incandescent lamp characteristics provided with an arc tube 12 having a discharge-sustaining filling comprising a predetermined amount of mercury plus a small pressure of inert ionizable gas and predetermined amounts of sodium iodide, tin iodide and thallium iodide. The lamp is provided with an outer envelope 14 carrying on the inner surface thereof a luminescent coating 22 comprising a mixture of predetermined amounts of strontium chloroapatite phosphor activated by divalent europium and yttrium vanadate phosphate phosphor activated by trivalent europium in predetermined proportion. <IMAGE>

Description

SPECIFICATION Metal halide high-intensity discharge lamps This invention relates to metal halide highintensity-discharge lamps and, in particular, to metal halide lamps exhibiting enhanced color rendition of illuminated objects.

One such lamp is disclosed in U.S. Patent No. 3,670,194 (Thornton, Jr. et al). The Thornton lamp utilizes a two-component blend phosphor coating on the inner surface of the outer envelope. One of the phosphor blend components provides an emission in the shorter wavelength region of the visible spectrum peaking at from 440 nm to 470 nm, such as, strontium chloroapatite activated by divalent europium, and the other phosphor blend component provides an emission in the longer wavelength region of visible spectrum peaking at from 605 nm. to 630 nm. such as, yttrium phosphate vanadate activated by trivalent europium.

Another such lamp is disclosed in U.S.

Patent No. 3,825,792 (Rokosz et al). The Rokosz lamp utilizes a coating on the inner surface of the outer envelope comprising a phosphor mixture of europium activated yttrium phosphate vanadate or yttrium vanadate and manganese activated magnesium fluorogermanate or magnesium-arsenate.

In French Patent Publication No.

2,229,139, dated December 6, 1974, is disclosed a high-pressure metal vapor lamp carrying a phosphor coating on the inner surface of the outer envelope. The coating comprises red-emitting yttrium vanadate phosphate phosphor activated with trivalent europium with the addition of a non-fluorescent yellow pigment-reaction product of NiO and TiO2.

In Japanese Patent No. 43-20514 dated September 3, 1968, issued to Nihon et al. is disclosed a high-pressure metal discharge lamp having electrode vessels containing an addition of from 2 to 3 iodine compounds, for example, iodides of sodium, thallium and indium.

Accordingly, the present invention resides in a metal halide high-intensity discharge lamp with incandescent lamp characteristics, said lamp including an elongated radiationtransmitting arc tube which is enclosed by and supported within a light-transmitting protective outer envelope, said arc tube having operating electrodes operatively positioned therein proximate the ends thereof and a starting electrode positioned in close proximity to one of said operating electrodes, said arc tube enclosing a discharge-sustaining filling comprising a predetermined amount of mercury plus a small pressure of inert, ionizable gas; predetermined amounts of sodium iodide, tin iodide and thallium iodide, said outer envelope carrying on the inner surface thereof a luminescent coating comprising a mixture of predetermined amounts of strontium chloroapatite phosphor activated by divalent europium and yttrium vanadate phosphate phosphor activated by trivalent europium in predetermined relative weight proportions, electrical lead-in means sealed through said arc tube and connected to said electrodes, electrical adapter means affixed to the outer surface of said outer envelope to facilitate electrical connection of said lamp to a source of electrical power, and said electrical adapter means electrically connected to said lead-in means.

In order that the invention can be more clearly understood, a convenient embodiment thereof will now be described, by way of example, with particular reference to the accompanying drawings in which: Figure 1 is an elevational view, shown partly in section, of a metal halide lamp showing the location of the luminescent coating; and Figure 2 is a graph of relative energy versus wavelength showing the spectral output of the lamp of Fig. 1.

Referring to Fig. 1 a metal halide highintensity discharge lamp 10 includes an elongated radiation-transmitting arc tube 1 2 typically made of quartz. The arc tube 1 2 has operating electrodes 1 8 operatively positioned therein proximate the ends thereof. Starting electrode 20 is positioned in close proximity to one of the operating electrodes 1 8. The arc tube 1 2 is enclosed by and supported within a light-transmitting outer envelope 14.The arc tube 1 4 encloses a discharge-sustaining filling 1 6 comprising a predetermined amount of mercury such as, 12.5 mg./cm. of spacing between the operating electrodes, plus a small pressure of inert, ionizable gas, such as argon at about 25 torrs, for example, as is well known in the art. The discharge-sustaining filling 1 6 further comprises predetermined amounts of sodium iodide from 6.5 to 18.0 mg./cm. of spacing between the operating electrodes, tin iodide from 0.3 to 1.0 mg./cm. of spacing between the operating electrodes and thallium iodide from 0.1 to 0.6 mg./cm. of spacing between the operating electrodes.

The outer envelope 1 4 carries on the inner surface thereof a luminescent coating 22 comprising a mixture of predetermined amounts of strontium chloroapatite phosphor activated by divalent europium preferably from 0.2 to 0.8 mg./cm2 of coating and yttrium vanadate phosphate phosphor activated by trivalent europium from 1.0 to 2.5 mg./cm.2 of coating in predetermined relative weight proportions as hereinafter described.

The strontium chloroapatite phosphor may be prepared, for example, by mixing 0.6 mol of SrHPO4, 0.27 mol of SrCO3, 0.11 mol of SrCI2 and 0.02 mol of EuCO3. Added to this raw mix is 0.25 mol of additional SrCI2 which serves as a flux during firing. The raw mix is then fired in a reducing atmosphere, for example, a 90 percent nitrogen-1 0 percent hydrogen atmosphere at from 900 to 1 ,200'C and preferably at 1,100"C for about 3 hours. After cooling, the phosphor is broken up and leached with distilled water to remove residual soluble strontium chloride flux. The phosphor has an emission peak at about 446 to 450 nm and its output comprises a narrow band in the shorter wavelength regions of the visible spectrum.

The yttrium phosphate vanadate phosphor has an emission peak at about 620 nm. Such a phosphor is well known in the phosphor art and is used to color correct the output of mercury lamps. As an example of preparing this phosphor, equal mol parts of yttrium vanadate and yttrium phosphate are mixed with the required activator and the mixture is fired at 1,150"C for 6.5 hours and in air atmosphere. Alternatively, yttrium vanadate activated by europium could be used instead of the vanadate-phosphate and the spectral emissions of these two phosphors are substantially identical.

Both of these phosphors have approximately the same quantum efficiency. Accordingly, the relative wattage output of the short wave emission of one phosphor component to the relative wattage output of the long wave emission of the other phosphor component is substantially equal to the relative weight ratios of these phosphors. In order to have an acceptable overall color rendering index, the relative weight proportion of the short wave emitting phosphor (strontium chloroapatite phosphor) to the long wave emitting phosphor (yttrium vanadate phosphate) should be from 0.05:1 to 0.4: 1, a better color rendering index is achieved with a relative weight proportion of from 0.1:1 to 0.3:1. The preferred relative weight proportion is about 0.2:1.

The lamp further includes electrical lead-in means 24 which are sealed through the arc tube 1 2 and connected to the operating electrodes 1 8 and starting electrode 20. Electrical adapter means 26 is affixed to the outer surface of the outer envelope 14 to facilitate electrical connection of the lamp to a source of electrical power 28. The electrical adapter means 26 typically comprises a metallic shell portion 30 and a metallic eyelet 32 separated by an electrical insulating means 34. The electrical adapter means 26 is electrically connected to the lead-in means 24.

The luminescent coating 22 is applied as a coating to the inner surfaces of the outer envelope 14. The application of the coating may be accomplished by electrostatic deposition, as described in U.S. Patent No.

3,358,639, issued to Lopenski et al., which may be referred to for further detail reference, or by applying the coating in a lacquer vehicle and heating to decompose the organic binder.

A 400-watt metal halide lamp was made in accordance with this invention. The lamp included an arc tube having dimensions of 1 8 mm X 22 mm and 45 mm of spacing between electrodes. The arc tube contained 56 mg. of mercury and argon at 25 torr together with 58.0 mg. of sodium iodide, 1.6 mg. of thallium iodide and 2.5 mg. of tin iodide. The inner surface of the outer envelope 1 4 was coated with a mixture of strontium chloroapatite and yttrium vanadate phosphate phosphors in the following amounts: strontium chloroapatite 0.4 mg./cm.2 of coating and yttrium vanadate phosphate 1.6 mg.cm2 of coating.

Referring to the graph of Fig. 2 lamp data is given for the lamp described above, along the abscissa indicated is the wavelength of light emitted and along the ordinate is indicated the relative energy of that light. This lamp produces x - y, C.l.E. coordinates of x = 0.433 and y = 0.4195. The lamp has a color rendition of illuminated objects of 63.5 and an efficacy of 66 lumens per watt and a correlated color temperature of 3174"K.

These results are very favorable when compared to the lamps of prior art which typically had an initial efficacy of 48 lumens per watt, color rendition of illuminated objects of 52 and a correlated color temperature in the range of 3000-3300"K.

Claims (4)

1. A metal halide high-intensity discharge lamp with incandescent lamp characteristics, said lamp including an elongated radiationtransmitting arc tube which is enclosed by and supported within a light-transmitting protective outer envelope, said arc tube having operating electrodes operatively positioned therein proximate the ends thereof and a starting electrode positioned in close proximity to. one of said operating electrodes, said arc tube enclosing a discharge-sustaining filling comprising a predetermined amount of mercury plus a small pressure of inert, ionizable gas; predetermined amounts of sodium iodide, tin iodide and thallium iodide, said outer envelope carrying on the inner surface thereof a luminescent coating comprising a mixture of predetermined amounts of strontium chloroapatite phosphor activated by divalent europium and yttrium vanadate phosphate phosphor activated by trivalent europium in predetermined relative weight proportions, electrical lead-in means sealed through said arc tube and connected to said electrodes, electrical adapter means affixed to the outer surface of said outer envelope to facilitate electrical connection of said lamp to a source of electrical power, and said electrical adapter means electrically connected to said lead-in means.

2. A lamp according to claim 1, wherein the sodium iodide is present in amount from 6.5 to 18.0 mg./cm. of spacing between the operating electrodes, the tin iodide is present in amount from 0.3 to 1.0 mg./cm. of spacing between said operating electrodes and the thallium iodide is present in amount from 0.1 to 0.6 mg./cm. of spacing between said operating electrodes.

3. A lamp according to claim 1 or 2, wherein the strontium chloroapatite phosphor activated by divalent europium is present in amount from 0.2 to 0.8 mg./cm.2 of coating and said yttrium vanadate phosphate phosphor activated by trivalent europium is present in amount from 1.0 to 2.5 mg./cm.2 of coating, and the relative weight proportion between said strontium chloroapatite phosphor to said yttrium vanadate phosphate is from 0.05:1 to 0.4:1.

4. Metal halide high-intensity discharge lamps as claimed in claim 1 and substantially as described herein with particular reference to the accompanying drawings.