EP0714551B1 - Metal-halide discharge lamp for photographic-lighting purposes - Google Patents

Abstract

Described is a metal-halide discharge lamp for photographic-lighting purposes, the lamp containing between 0.1 to 4.5 mg/cm3 of A1I¿3?. Other, preferred, components of the gas in the lamp are halides of mercury, indium, thallium or caesium.

Description

The invention is based on a metal halide discharge lamp according to the preamble of claim 1.

Such lamps can be used, for example, for video projection, endoscopy or also for medical technology (operating room lights). They are particularly suitable for video projection in liquid crystal technology (LCD), in particular also for large-screen television screens with an aspect ratio of 16: 9. Typical power levels are 100 to 500 W.

The use of aluminum in the discharge vessel of lamps has been known for a long time. However, it is problematic with regard to the hygroscopic behavior of the aluminum compound during the filling process and the strong attack on the electrodes during the service life, so that this is greatly restricted. Accordingly, the use of aluminum-containing fillings has hitherto been limited to either electrodeless lamps (e.g. US-A 4,672,267 or 4,591,759) or lamps in which the electrodes are specially coated in order to achieve a suitable chemical conversion of the aluminum, e.g. DE-A 24 22 576.

US Pat. No. 3,586,898 uses AlCl ₃ and metallic aluminum as the filling for light formation. Ceramic or quartz glass coated with Al ₂ O ₃ is used as the discharge vessel. A small amount of AlJ _{3 can be} added to reduce electrode corrosion.

Finally, from DE-PS 1 539 516 a metal halide lamp with a wall load of more than 40 W / cm ^{2 is} known, in which a filling is introduced in a discharge vessel with activated electrodes, which contains either aluminum chloride or bromide. Such fillings, however, tend to have very short lifetimes in the order of 100 hours. They should produce a spectrum similar to daylight, with a high load being accepted.

Furthermore, from EP-A 459 786 a lamp for photo-optical purposes and a long service life is known, in particular for video projection, which contains mercury and argon as filling components iodides of the rare earths dysprosium and neodymium as well as cesium. Rare earth fillings have hitherto been customary for lamps of this type, since they ensure good color rendering with high luminous efficacy. We hereby expressly refer to the content of this document.

Although rare earth fillings are very suitable for general lighting purposes, they only meet the high requirements for photo-optical purposes to a limited extent. The cause is that large amounts of rare earth metals attack the discharge vessel, which is usually made of quartz glass, which slowly leads to devitrification at the high operating temperatures and ultimately also increases the risk of bursting. The devitrification deteriorates the optical characteristics of such lamps so significantly (diffuse imaging of the arc) that the lamps for photo-optical purposes, where it is an exact imaging of the arc by the optical system arrives, are no longer usable. After all, the maintenance of these lamps is also unsatisfactory. Furthermore, the formation of light in rare earth metals mainly results from molecular electron transitions that occur at the edge of the arc, so that, for example, color fringes can appear on the projection screen when used for projection purposes (poor color uniformity).

It is an object of the present invention to provide a lamp for photo-optical purposes which is distinguished in particular by a long service life, good maintenance and homogeneous color distribution, and also shows good color rendering.

This object is achieved by the characterizing features of claim 1. Particularly advantageous designs can be found in the subclaims.

Metal halide lamps for photo-optical purposes generally have an electrode spacing of at most 15 mm. In order to create a light source that is as punctiform as possible, preferred values are between 2 and 8 mm. The color temperature is higher than 5000 K, especially 6000-10 000 K.

The lamp according to the invention is distinguished by a filling which contains 0.1 to 4.5 mg / cm ³ AlJ ₃ as the essential or only metal halide component. The addition of aluminum in this form has two advantages. On the one hand, precise dosing of even small amounts of Al is possible, since the atomic weight of the binding partner iodine is very high. On the other hand, iodine is particularly good for the halogen cycle in the present case suitable and attacks the electrodes less than chlorine or bromine. Another advantage is that this filling system is so insensitive that the same filling can be used for different wattages without changing the color temperature. Finally, the influence of iodine on the lamp spectrum (absorption in the blue) is also desirable.

Depending on the electrode configuration, it may also be advantageous to add up to 2.0 mg / cm ³ AlBr ₃ .

AlJ ₃ has so far been regarded as unsuitable because the luminous efficacy that can be achieved with it is relatively low (approx. 70 lm / W) compared to conventional rare earth fillings (approx. 100 lm / W). However, this did not take into account the fact that the light yield, based on the entire optical structure, ie measured in the associated reflector and with the greatest possible parallelism of the light beam (divergence angle <5 °), is significantly better compared to conventional systems, so that the Overall system yield becomes comparable. This is because the light is generated by means of atomic transitions, which mainly take place in the arc core, so that the color separation is considerably restricted.

• R = 600 nm bis 650 nm
• G = 500 nm bis 540 nm
• B = 400 nm bis 500 nm.

Finally, a particularly important advantage is that the color rendering that can be achieved with AlJ ₃ matches the requirements profile particularly well. The so-called R / G / B distribution is an essential parameter for determining the color rendering, in particular for video projection. Below that is the relative Understand the intensity distribution in three selected wavelength ranges, namely red (R), green (G) and blue (B). These areas are defined as follows:

• R = 600 nm to 650 nm
• G = 500 nm to 540 nm
• B = 400 nm to 500 nm.

Conventional fillings show an increase in the green area (and less pronounced the blue area) at the expense of the red component, e.g. R / G / B = 18:67:15.

• R = 25 % bis 35 %
• G = 50 % bis 65 %
• B = 8 % bis 18 %.

With aluminum iodide as the basic component, R / G / B values can be achieved due to the uniformity of its spectrum, which show a significantly higher red component:

• R = 25% to 35%
• G = 50% to 65%
• B = 8% to 18%.

InJ (or another halide of indium) and possibly a halide of mercury (for example HgJ ₂ , HgBr ₂ ) in a total amount of up to 2.0 mg / cm ³ , preferably up to 1, are particularly suitable as further filling additives for fine tuning. 0 mg / cm ³ Using halides of indium, for example, the blue content can be fine-tuned. The halides of thallium and / or cesium are suitable as additional filler additives (up to 1.0 mg / cm ³ ) for fine-tuning the proportion of green or for stabilizing the arch. Finally, a slight addition of rare earth metals, preferably in metallic form, is possible to fill the spectrum, in particular between approximately 500 and 600 nm, in an amount of up to 0.5 mg / cm ³ . Thulium are preferred and dysprosium, especially in an amount up to 0.1 mg / cm ³ . This amount is so small that the resulting devitrification can be neglected.
Iodine and / or bromine are generally preferred as halides, a mixture adapted to the geometry and volume inhibiting the electrode erosion.

A particular advantage is that the electrodes in the present filling do not have to be specially treated in any way, ie for example no coating (for example with scandium or thorium oxide, as previously known) is necessary. Electrodes in which a coil is pushed onto a shaft are particularly suitable, the shaft material consisting of tungsten which is doped with a material having a low electron work function (for example ThO ₂ ), while the coil advantageously consists of undoped tungsten.

Quartz glass is suitable as the bulb, in particular a bulb pinched on two sides, which is covered, for example, at one or both ends with a heat layer (for example ZrO ₂ ). Under certain circumstances, the homogeneity of the light and color distribution, as known per se, can be improved by matting.

In principle, a bulb made of ceramic material (Al ₂ O ₃ ) is also suitable, as is already known for other lamp types. The lamp is advantageously combined with a reflector to form a structural unit, as described in EP-A 459 786. The lamp is mounted approximately axially in the reflector. The reflector has a dichroic coating, for example.

The lamp is particularly suitable for projection technology on the basis of liquid crystals, which is also suitable as a basis for high-definition television (HDTV). As a lighting medium, this technology requires a discharge lamp with special properties, in particular with regard to the optimal balance of the R / G / B components, the usable screen luminous flux and the luminance. Other features include lifetimes of more than 2000 hours, high maintenance (if possible over 50%) with regard to color location and intensity as well as parallel light emission. A high luminance and maintenance of the color location and the intensity is necessary because the optical system efficiency is ultimately only 1 to 2%. Since the angular acceptance of liquid crystals (LCD) is only a maximum of 5 °, extremely parallel light is necessary, which is synonymous with the requirement for the best possible point light source. In general, however, this will affect lamp life. Other essential requirements are the homogeneity of the color temperature and the illuminance distribution on the projection screen.

A filling system with up to 4.5 mg / cm ³ AlJ ₃ and up to 2.0 mg / cm ³ InJ is particularly suitable. Both components generate light through atomic transitions, so that color fringing is also avoided here. A general advantage of the filling is that the color proportions and their proportions vary only slightly over the lifespan.

In a particularly preferred embodiment, the lamp consists of a quartz glass discharge vessel squeezed on both sides with axially arranged ones Tungsten electrodes. This is installed in a paraboloid reflector with a dichroic coating, the diameter of the reflector being matched to the diagonals of the liquid crystal array (LCD). The coating of the reflector corresponds to an optical bandpass, which reflects the visible spectrum and transmits IR and UV components. An increased uniformity of the color and intensity distribution in the LCD level can be achieved by suitable matting of the discharge vessel. A heat accumulation layer is often attached to one or both of the vessel ends surrounding the electrodes. The lamp is operated with a known electronic ballast, which also ensures hot re-ignition.

Fig. 1

eine schematische Darstellung der Lampe mit Reflektor

Fig. 2

das Spektrum einer Lampe

Fig. 3-8

Meßergebnisse hinsichtlich des Lichtstroms, der Farbtemperatur sowie des Farborts für verschiedene Füllungen

Several exemplary embodiments are described in more detail below with reference to the figures. It shows:

Fig. 1

a schematic representation of the lamp with reflector

Fig. 2

the spectrum of a lamp

Fig. 3-8

Measurement results regarding the luminous flux, the color temperature and the color location for different fillings

1 shows a metal halide lamp 1 with a power of 170 W and a discharge vessel 2 made of quartz glass, which is squeezed 3 on two sides. The discharge volume is 0.7 cm ³ . The axially opposite electrodes 4 are 5 mm apart. They consist of an electrode shaft 5 made of thoriated tungsten onto which a helix 6 made of tungsten is slid. The shaft 5 is connected to an external power supply 8 in the area of the pinch 3 via a film 7.

The lamp 1 is arranged approximately axially in a parabolic reflector 9, the arc that is formed between the two electrodes 4 in operation being in the focus of the paraboloid. A part of the first pinch 3a sits directly in a central bore of the reflector and is held there in a base 10 by means of cement, the first power supply line 8a being connected to a screw socket contact 10a.
The second pinch 3b faces the reflector opening 11. The second power supply line 8b is connected in the area of the opening 11 to a cable 12 which, in isolation from the wall of the reflector, is returned to a separate contact 10b. The outer surfaces of the ends 13 of the discharge vessel are coated with ZrO ₂ for heat accumulation purposes. The central part 14 of the discharge vessel is matted in order to improve the uniformity.

• 1,15 mg AlJ₃
• 0,1 mg InJ
• 0,36 mg HgBr₂

In addition to 200 mbar, the filling of the discharge volume contains argon and mercury in a first exemplary embodiment:

• 1.15 mg AlJ ₃
• 0.1 mg InJ
• 0.36 mg HgBr ₂

The spectrum of this lamp is shown in Fig. 2. This results in an R / G / B ratio of 26:58:16. The wall load is approx. 35 W / cm ² . When filling the AlJ ₃ , the purity is as good as possible pay particular attention to the absence of oxygen.
In a second and third exemplary embodiment, the following are used:
1.15 mg AlJ ₃ or 1.15 mg AlJ ₃ and 0.05 mg Tm. The R / G / B ratio is 29:55:16 and 28: 57.5: 14.5.

In a fourth embodiment, 0.05 mg Tm is added to the first embodiment. This achieves an R / G / B ratio of 26.5: 57.5: 16. The corresponding spectrum is shown in FIG. 8. There, the spectrum without Tm (curve a) from FIG. 2 is compared with that of the Tm-containing filling (curve b). The thulium mainly fills the spectrum between 510 and 630 nm.

With these fillings, good color uniformity is achieved in the projection and an excellent consistency of the color temperature T _n over a service life of 2000 hours; the maintenance is 70%. The color locus is x = 0.295 and y = 0.317.

The color temperature T _n can be adjusted by varying the amount of AlJ ₃ , with initial values of T _n between 6000 and 10,000 K.

• 0,45 - 3,3 mg/cm³ AlJ₃
• 0 - 0,3 mg/cm³ In-Halogenid, insbes. InJ
• 0 - 0,7 mg/cm³ Hg-Halogenid, insbes. HgBr₂
• 0 - 0,7 mg/cm³ Halogenide des Cs u/o Tl

Particularly good results in terms of service life and maintenance can be achieved with the following fillings:

• 0.45-3.3 mg / cm ³ AlJ ₃
• 0 - 0.3 mg / cm ³ In-halide, especially InJ
• 0 - 0.7 mg / cm ³ Hg halide, in particular HgBr ₂
• 0 - 0.7 mg / cm ³ halides of Cs and / or Tl

• A) 2,3 mg AlJ₃, 0,1 mg InJ, 0,36 mg HgBr₂
• B) 1,15 mg AlJ₃, 0,1 mg InJ, 0,36 mg HgBr₂
• C) 0,6 mg AlJ₃, 0,1 mg InJ, 0,36 mg HgBr₂
• D) 0,3 mg AlJ₃, 0,1 mg InJ, 0,36 mg HgBr₂

3 and 4, the maintenance of the luminous flux is within an angle of 5 ° (so-called "panel lumen") in relative units or the course of the color temperature in each case over a burning time of more than 2000 hours for different fillings at one 170 W lamp (volume 0.7 cm ³ ) specified. The discharge vessel was coated with ZrO ₂ , but without matting. The individual fillings are

• A) 2.3 mg AlJ ₃ , 0.1 mg InJ, 0.36 mg HgBr ₂
• B) 1.15 mg AlJ ₃ , 0.1 mg InJ, 0.36 mg HgBr ₂
• C) 0.6 mg AlJ ₃ , 0.1 mg InJ, 0.36 mg HgBr ₂
• D) 0.3 mg AlJ ₃ , 0.1 mg InJ, 0.36 mg HgBr ₂

3 that the maintenance after 2000 hours is in the order of 60-75%. After 3000 hours it is still 50-65% and still meets the minimum requirements. The absolute value of the luminous flux is highest with a low Al dosage D) and decreases with increasing Al dosage. The drop in the course of the burning time is roughly independent of the amount of aluminum.

4, the color temperature T _{n is} inversely proportional to the Al dosage. It is extremely constant over the burning time. Color temperatures around 8000 K are generally preferred for video projection, corresponding to a dosage of 0.6 to 1.15 mg, corresponding to a volume-independent dosage of 0.85 to 1.65 mg / cm ³ .

The combination of both figures shows a great advantage of these fillings, namely that Various requirements, for example with regard to the color temperature, can be made without large changes in the filling, apart from the amount of AlJ ₃ and other technical properties of the lamp.

Fig. 5 shows for fill B) the color locus (x or y value) as a function of the service life (initial value after 1 hour, value after 1000 and 2700 hours) and the location (nine measuring points E1-E9, which are uniform over the surface of the projection screen as a 3x3 matrix). The x value fluctuates only slightly between the values x = 0.28 and x = 0.29; the y value between y = 0.295 and 0.31.

6 and 7 show the behavior of a 200 W lamp, which is otherwise constructed similarly to the 170 W lamp. The fillings used here are on the one hand identical to filling C), and on the other hand the following filling E) was used: E) 0.9 mg AlJ ₃ , 0.1 mg InJ, 0.36 mg HgBr ₂ .

FIG. 6 shows the illuminance on a projection screen in lux, averaged over the grid of nine measuring points described in FIG. 5 as a function of the burning time, while FIG. 7 shows the color temperature as a function of the burning time.

Here, too, the insensitivity of the AlJ _3- based filling system to special adaptations to special requirements is confirmed.

In general, the addition of small amounts of rare earth metals can extend the life of the invention Shorten the lamps a little. This is countered by an increase in light output (by up to 10%) and a decrease in color temperature (up to 500 K).

Claims (10)

1. Metal halide discharge lamp for photo-optical purposes having a transparent discharge tube (2) which contains an aluminium-containing filling, in which two electrodes (4) which are connected to current leads (8) led to the outside face each other, characterized by the following features:

   - the filling contains the following components:

   0.1-4.5 mg/cm³ AlI₃ as essential or sole metal halide component for the generation of light

   0 -2.0 mg/cm³ halides (Ha) of indium (InHa) and/or mercury (HgHa₂)

   - the electrode separation amounts to a maximum 15 mm

   - the colour temperature amounts to at least 5,000 K.
2. Lamp according to Claim 1, characterized in that the filling additionally contains up to 1.0 mg/cm³ halide of thallium (TlHa) and/or of caesium (CsHa₂).
3. Lamp according to Claim 1 and 2, characterized in that the filling additionally contains up to 0.5 mg/cm³ rare-earth metals.
4. Lamp according to one of the preceding claims, characterized in that the filling additionally contains up to 2.0 mg/cm³ AlBr₃.
5. Lamp according to Claim 1, characterized in that the lamp forms a constructional unit with an optical reflector (9).
6. Lamp according to Claim 1, characterized in that the electrodes (4) are prepared from tungsten, the electrode or a part thereof being able to be doped with a material of low electron work function.
7. Lamp according to Claim 6, characterized in that the electrode (4) is uncoated.
8. Lamp according to one of the preceding claims, characterized in that the relative intensity distribution over three selected wavelength regions R/G/B with

   R = 600 nm to 650 nm

   G = 500 nm to 540 nm

   B = 400 nm to 500 nm

   amounts to

   R = 25% to 35%

   G = 50% to 65%

   B = 8% to 18%.
9. Lamp according to Claim 1, characterized in that the electrode separation amounts to between two and eight millimetres.
10. Lamp according to Claim 1, characterized in that the discharge tube (2) is a quartz glass bulb pinched on two sides, which is optionally wholly or partly coated.

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