HU189968B - High pressure sodium vapour discharge lamp with improved electrode - Google Patents

Abstract

In a high-pressure sodium vapour discharge lamp according to the invention, an emitter (19) is used which comprises strontium yttrate. It has been found that the lamp has a comparatively long life. This becomes clearly manifest in a low-power lamp which during operation emits <<white>> light.

Description

The present invention relates to a high pressure sodium discharge lamp having a vacuum sealed ceramic discharge tube filled with sodium, hogan and noble gas, the wall of which passes through a current conductor to an electrode having a strontium emitting material.

Such a lamp is known from British Patent No. 2,051,470. This known lamp is designed to emit substantially white light during operation, i.e., having a color temperature of approximately 2250 and approximately 2750 K, and a general color rendering index of Rag of approximately 60 and 85. The electrodes contain an emitting material containing oxygen-bound strontium and oxygen-bonded tungsten in a ratio of 3 to 50 molar. In the known lamps, this emitter is used because it counteracts the desire for sodium to discharge.

High-pressure sodium vapor discharge lamps produce white light, the temperature of the sodium amalgam in the lamp during operation is higher, and thus a greater proportion of sodium is drawn from the discharge than high-pressure sodium lamps emitting golden light. This can be explained by the chemical reactions that produce the sodium compounds and thus the sodium is removed from the discharge which is formed faster the higher the lamp temperature.

The temperature of sodium amalgam in high-pressure sodium discharge lamps increases with decreasing power. This is due to the smaller size of the low-power lamps. The temperature of the sodium amalgam in a 50 W high-pressure sodium lamp emitting white light is approximately 1200 K.

In known lamps, the use of said emitter is effective against sodium depletion. Although it has been found that white light bulbs have very low power, such as 50 W, so that at high temperatures, sodium is still discharged to such an extent that the lamp life is too short for practical use,

It is an object of the present invention to provide a high pressure sodium discharge lamp which emits white light at very low power and has a sufficiently long service life for practical use.

The sputtered target was achieved with the high pressure sodium discharge lamp described in the introduction, wherein the emitting material contains strontium ittrate.

It has now been found that, even when the lamp is designed to operate at very high temperatures during operation,

For example, in a lamp that emits white light and consumes 50 watts, the lamp has a significantly longer lifetime for practical use. At the end of the lifetime of a high-pressure sodium discharge lamp, the voltage on the lamp increases to the point that the lamp goes out or, for lamps designed to emit white light, the end of the lifetime occurs when the color temperature of the emitted light goes out. Both the shift in color temperature and the increase in lamp voltage are due to the fact that the Na / Hg ratio in the lamp charge decreases as sodium is withdrawn from the lamp charge.

The range of the color triangle within which the light of the high pressure sodium discharge lamp can be considered white is delimited by the lines x 0, 0.460, x 0.495, y = 0.408 and y = 0.425. By far stricter standards, white light is much more acceptable, and the range of white light within the color triangle is defined by the lines x 0.468, x = 0.490, y 0.408, and y »= 0.425. The color temperature is between about 2300 and 2700 K and the Rao overall color rendering index is between about 70 and 85.

The high-pressure sodium discharge lamp of the present invention may be prepared, inter alia, by dipping the electrodes in a suspension of SrCO3 and Υοθ2. After they have dried, the electrodes are heated and the emitter is molded in place. For this purpose, heating for a few minutes, for example two minutes, at 1600 ° C under vacuum or in an inert gas atmosphere is sufficient. The advantage of the emitter is that its electrodes, which are well resistant to moisture, and thus provided with the emitter, can be handled well in the ambient atmosphere.

Other strontium salts, such as form, or, for example, strondum hydroxide or peroxide, may be used in the formation of the emitter in place of the strontium carbonate. A number of other strondum compounds are further possible.

Most of the lamps of the invention have a ceramic discharge tube, i.e. the discharge tube consists of a mono- or polycrystalline material, such as aluminum oxide. Charging the lamp discharge tube - in the case of a lamp having to emit white light a gas containing sodium amalgam within a Na / Hg weight ratio of 1-1 / 9 while the pressure of the noble gas such as xenon and / or pressure of argon and / or neon at 300 K

1.3 x 10 - 1.3 χ 10 ⁵ Pa. The pressure of the sodium during the operation of the lamp is then 4x10 ^ - 10.7x10 ⁴ Pa.

An embodiment of a lamp according to the invention will be described in more detail with reference to an example of an embodiment shown in the accompanying drawings, in which

Figure 1 is a partially broken away view of a high pressure sodium discharge lamp, a

Figure 2 is a longitudinal section through the discharge tube of the lamp of Figure 1.

In Figure 1, a ceramic discharge tube 3 is vacuum sealed and disposed in a discharge glass bulb 1 between current conductors 4 and 5, and the bulb 1 has a head 2.

The niobium sleeves 6 and 7 conduct the current through the wall of the discharge tube 3 to the pair of electrodes. The conductor 5 extends into the niobium sleeve 6 with a certain degree of play. Between these parts an 8 Litze wire ensures good electrical contact.

The outer bulb 1 has a vacuum maintained by a barium getter evaporated from the ring 9.

In the outer bulb 1 is placed a coals 10 and connected in series with a blast metal switch 11 which are connected in parallel with the discharge path of the discharge tube 3. When the lamp is lit, a glow discharge occurs in the glow igniter 10. After this incandescent light has gone out, due to the increased temperature in the incandescent lamp 10, a voltage pulse is generated at

169,968 on the electrodes of the frying tube, which causes it to ignite. The heat generated by the discharge opens the blast metal switch 11.

As shown in Fig. 2, the discharge tube 3 extends through a vial 6 of a ceramic material from a niobium and is secured thereto by a binder 16. For example, the composition of the binder 16 is as follows:

32.6% A1, CK,

50.4% Cat>,

4.2% BaO,

10.3% MgO,

0.1% SrO,

1.8% B ₂ O ₃ ,

0.5% SiO _2>

0.1% Na ₂ O, or

20.1% Al ₂ O _3>

69.4% CaU,

6.0% BaO,

3.5% MgO,

1.0% B ₉ O (% mol%)

A tungsten electrode 17 is welded to the sleeve 6 on which a tungsten wire 18 is wound, which encloses an emitter 19.

Example

In a practical embodiment, the discharge tube had an internal diameter of 3.5 mm and an internal length of 25 mm. The electrode tip spacing was 15 mm. Each electrode contained 2 mg of emitter in the cavity between the threads. The discharge tube contained 10 mg of sodium amalgam with a Na / Hg ratio of 0.375 and a xenon pressure of 10 ⁴ Pa at room temperature. The lamp consumed 50 W during operation.

Such lamps are provided with emitting material produced in various ways and tested in the following order. 5.5 hours on, 0.5 hours off. It has been found that the lamps tested reach their end-of-life by a few hours with this on-off test method, due to the increased voltage on the lamp, than when the lamps are tested for 0.5 hours,

They are off for 0.5 hours or as compared to continuous operation.

The lamps (L) used as electrodes of a first series, which have been set up in March ^ 5 to a suspension of 290 g of SrCo _3, 220 g Y7Ó3 ^v ° li szuszpnendáltatva 100ml monoetu-glycol, 60 ml of butyl acetate and 5 g of cellulose nitrate.

The electrodes were dried and heated under vacuum at 1590 ° C for 2 minutes. Then SrY ₂ O ^, was formed.

for comparison, electrodes of a second series _of lamps (II) were immersed in a suspension of the following composition:

155 g of SrCO ₃ was by suspending in 55 ml of ethylene glycol, 23 ml of ethyl alcohol, 5 ml of butyl acetate and 1.5 g of nitrocellulose. After this slurry was dried, the electrodes were heated at 1450 ° C for 2 minutes in a vacuum.

The molar ratio of Sr to W in the emitter was about 10.

The results of experiments with these lamps are given in the table below:

¹⁵ TABLE

Serial V, (V) x, y Vj (V) x, y Lifetime after 1CJCF hours ... hours L (hours)

I 81 0.483,0,418 88 0.486,0,414 L3000

1500

II 85 0.477,0,417 89 0.487,0,411 1500 <L <

Vi is the voltage on the lamp.

The condition for this experiment was that when 50% of the tested lamps had a color temperature outside the area defined by the lines X = 0.468, X = 0.490, Y »0.408 and y« 0.425, the lamp had reached the end of its life. end.

The Series I lamps were tested after 3,000 hours of operation. Of the seven lamps examined, five had color points within that range. The mean values of the color points of these five lamps are shown in the table. The experiment was completed in this condition.

The Series II lamps were tested after 1500 hours of operation. Thirteen of the nineteen lamps examined had an average color point shown in Table 1. After 2000 hours, only four lamps remain.

Claims (1)

A patent claim A high-pressure sodium discharge lamp having a vacuum-sealed ceramic discharge tube filled with sodium, mercury and noble gas, the wall of which passes through conductors to an electrode having a strontium-containing emitting material, characterized in that the emitter (19) Contains strontium ittrate.