SE467279B - DOUBLE WALL LOW PRESSURE GAS CHARGING LAMP SUPPLIED WITH SILOX SEALS - Google Patents

Abstract

By enveloping a gas discharge lamp, such as a fluorescent tube (2), in an outer glass tube (8), the discharge chamber of the fluorescent tube (2) is thermally insulated. This enables a sufficiently high temperature to be maintained in the fluorescent tube (2) for, e.g., mercury in the discharge chamber to be brought to a partial pressure at which good illuminating efficiency is obtained even at very low ambient temperatures around the lamp. The tubular envelope (8) is fixated at its ends to the fluorescent tube (2), in some suitable manner such as to surround the fluorescent tube and define a tubular space (10) of constant uniform width between the fluorescent tube and the surrounding envelope. In order to provide a lamp which will ignite readily, the occurrence of space charges between the fluorescent tube (2) and the outer tube (8) has been eliminated, by the provision of siloxane seals (11) between the inner fluorescent tube and the tubular envelope, at the respective ends thereof.

Description

467 279 extent is of the type with a reflector located above the fluorescent lamp, but without a cover. As the luminaires are equipped with covers, it is in the sense to protect the fluorescent lamp against mechanical damage, and the light replacement requirement has then been subordinated to the protection requirement. Although, when it comes to billboards, it is not as important to obtain a high light output as with luminaires for street lighting, rising prices for electrical energy will have an impact on the future design of such signs. Here, too, higher efficiency of the lamps will be required, which means that they must maintain a higher temperature at the coldest point of the mantle surface. For optimal light output, a temperature close to 40 ° C is required at this point.

Another area of use for fluorescent lamps, where these can be exposed to low ambient temperatures, is in tunnels. Even in tunnels several hundred meters long, the air flow through them is so great that any heat radiation from the surrounding rock or soil is not able to provide any additional heat to the surfaces of the fluorescent lamps. Thus, even in said applications, the luminous flux decreases exponentially with decreasing air temperature. This has a serious meaning if you consider that a car driver on a cold winter day with sunshine can see the road in an illuminance close to 100,000 lux. As this driver enters a road tunnel, his eyes must adjust to a lighting well below 100 lux. The traffic safety and safety feeling of the driver is promoted by the fact that the fluorescent lamps in the tunnel maintain a fairly normal luminous flux, even in very cold weather.

According to statistics, November is the month when most traffic accidents occur. These usually occur in the dark and are caused to a significant degree by poor street lighting. In those areas which consist of luminaires with low-pressure mercury vapor discharge lamps, the luminous flux from these lamps is halved 4: - can -1 ro -1 \ o between + 10 ° C and 0OC, in cases where conventional fluorescent lamps with an outer diameter of 38 mm2 are used. In recent years, there has been a transition from such fluorescent tubes to tubes 26 mm in diameter. The latter have been given a 10% lower effect than the former. This power reduction means an energy saving during the operation of the fluorescent lamps, but no significant decrease in the luminous flux at + 20o ambient temperature causes it. The conditions for lowering the ambient temperature from +20O to 0OC for a 58 W fluorescent lamp mean a reduction of the luminous flux from 4700 to 1400 lumens. In the temperature range + 10O - 0 ° C, for 26 mmzs, a reduction of the light flux to one third takes place. What makes the whole thing even more serious is that at + 10oC 26 mmzs tubes have a luminous flux, which is 20% lower than the luminous flux from a 38 mmzs tube of corresponding power.

As the narrower fluorescent lamps have increasingly been used, and are almost exclusively in demand, most manufacturers have discontinued their production of 38 mm diameter fluorescent lamps. Thereby, cathodes and other components have been completely adapted to the 26 mmzs tubes.

Now that the disadvantage of the narrower pipes has been noticed, components for 38 mmzs pipes could be manufactured again. However, this is not enough, but production lines would in several respects and at great cost need to be adapted for the larger pipe diameter.

A significant problem when using gas discharge lamps in low ambient temperatures is ignition. Normally used spark plugs short-circuit the electrodes, so that they are heated by surging current, so that, when the spark plug breaks, a spark switches from the anode to the cathode and a positive column is formed between them. At low ambient temperatures, the spark plug must be switched on and off several times, before the electrodes become hot enough to keep a spark alive between them. It can often take up to 467 279 half a minute to get the fluorescent lamp to light, and this disadvantage is markedly clearer with 26 mm tubes than with those of 38 mm diameter.

In order to solve the inconveniences associated with the use of narrow fluorescent lamps at freezing system temperature and to create a lamp with a high illumination efficiency at low temperatures, the present invention has been made. It is characterized in that a solid transparent tube, for example of glass, surrounds a narrow fluorescent lamp along its entire length, as well as in the other features which appear from the following claims.

It has surprisingly been found that if the gas in the gap between the fluorescent tube and the surrounding tube is dehumidified, the lamp becomes significantly more flammable at low ambient temperatures. This is probably due to the fact that in the absence of moisture, no space charges bearing ions are present next to the inner glass tube. This does not interfere with the formation of a positive column between the fluorescent tube electrodes. This arises when ions and electrons diffuse in the direction of the tube wall in the inner tube during the passage of the discharge current in the discharge chamber. Since the electrons are significantly much lighter than the positive ions, the electrons will reach the tube wall the fastest, as a result of which it will be negatively charged. Should positive space charges be available in the gap between the fluorescent tube and the outer tube, the charge of the tube wall on the side towards the discharge chamber would be neutralized, whereby it would be much more difficult to achieve a positive column between the electrodes.

The method of dehumidifying the gas in the gap between the two pipes, which has been found to be most effective, is to provide the lamp with seals of siloxanes at the pipe ends. These substances harden during the consumption of water, whereby alcohols are formed. The dipolarity of the water molecule means that it is far more charge-bearing than the electrically inert 'N 467 2.79 alcohols are. In this way, the generation of space charges is eliminated, and the lamp is easily lit even in severe cold.

A tubular discharge lamp according to the invention is surrounded by a glass tube, which may be transparent or opalescent.

Because this outer tube is fixed at its ends to the electrode-provided ends of the glass tube of the discharge lamp, a gap of constant width is maintained between the tubes. The fixing takes place by means of seals at the ends of the lamp between the two glass tubes. Such seals may be dense polymer rings, or otherwise be made of age-resistant, non-gas permeable material.

Regardless of how the outer tube is fixed, it is advantageous that the gap between the outer and inner tubes is filled with a clean gas, so that no light losses occur. Above all, dry, dust-free air comes into question here, but even a noble gas, or several such in a mixture, can be used in the gap with certain special requirements.

The gas in the gap can be kept at atmospheric pressure, but in order to increase the thermal insulating ability of the gap, in combination with the usually less than 1 mm thick pipe wall, the gas is preferably kept at negative pressure. The insulating ability also depends on the width of the gap, and this can be selected from 2-10 mm in the applications in question. In the case of fluorescent lamps with an outer diameter of 26 mm, which are surrounded by glass tubes with an outer diameter of 38 mm, the gap becomes approximately 5 mm wide. In the case of very narrow pipes and gaps over 10 mm, a heat-transporting air exchange between the outside of the inner tube and the inside of the outer tube can occur. This increases the convection, and part of the advantage of the invention is lost. An excessively narrow gap does not give the desired effect, unless it is completely evacuated. It has thus been judged that an optimal gap width is 4-8 mm. ac 467 279 To make maximum use of the light emitted, this can be directed, usually downwards, from the luminaire in which the lamp is used. Since the invention also aims to be able to be used in very simple luminaires, the inside of the outer tube can be coated, up to 1800, with a light and heat reflecting material. An advantage of this design is, in addition to an increase in the illuminance in the visible wavelength range, that reflection of heat radiation to the discharge space also takes place. The resulting increase in temperature in the discharge chamber corresponds to an increase in illuminance of more than 20% at an ambient temperature below + 10 °. Together with the light reflection, an increase in illuminance of between 50 and 60% can be achieved.

In addition to this, fluorescent lamps thus designed can be turned 1800 in luminaires provided with reflectors, whereby a type of top reflection is the result. This gives a soft light, and the lamp's self-heating is promoted.

The lamp according to the invention should be just such a solution to the lighting requirements, which have been expressed by those working on oil platforms in Arctic climates. In addition to the lamp at the low temperatures prevailing during the six dark months of the year provides a significantly higher light output than hitherto known discharge lamps, the outer tube provides protection against mechanical damage. Should this break, the inner tube can remain intact, and the lamp must remain lit, without the risk of any spark between the cathodes igniting around the platform of oil gas present. A safety lamp is thus offered here, which reduces the risk of explosion at oil platforms.

The invention is illustrated in the following drawing, where Fig. 1 shows a partially cut fluorescent lamp according to the invention, Figs. 2, 3 and 4 are diagrams of the ratio ambient temperature in OC - illuminance in lumen (Lm) for 18/20 W, 36 / 40W resp. 58/65 W fluorescent lamps. [2- m -a ro -a »o The lamp shown in Fig. 1 is a preferred embodiment of the invention, namely a double-walled fluorescent lamp 1. This consists of a fluorescent lamp 2 with a diameter of 26 mm, provided at both ends with sockets 3 with contact pins 4. The fluorescent tube 2 has in the usual way cathodes placed on clamping foot 5, in this case surrounded by cathode shields 6. Through the clamping foot 5 extends from the contact pins 4 to the cathode current conductor 7.

The fluorescent tube 2 is surrounded by an outer glass tube 8, 38 mm in diameter, which is transparent and slightly indented at its ends. The ends of this outer tube 8 protrude into annular grooves in polymer rings 9, which with press fit enclose the sockets 3.

By mounting the outer tube 8 by means of polymer rings 9 in a negative pressure chamber, to which only dry, filtered air is supplied, the air present in a gap 10 between the fluorescent tube 2 and the outer tube 8 will be dust-free. In addition, in use, the atmospheric pressure will contribute to the polymer rings 9 holding tightly between the glass tube 8 and the base 3.

In order to achieve a completely dry atmosphere in the gap 10, some side of the polymer rings 9 or corresponding seals 11 of some kind of siloxane are applied to the side facing the discharge space. For example, siloxane pulp can be introduced into the grooves in the polymer rings 9, in which the ends of the tube 8 are inserted, and a strict such mass is applied to the lamp tube 2 in immediate contact with the polymer ring 9.

In practice, 1.5 grams of polydimethylsiloxane pulp is used in connection with each end of the lamp. The active substance in the pulp consists of trimethylsiloxane monomers with the addition of catalyst and stabilizer. The monomer can be described by the general formula RxSi (OR ') y where R = methyl group OR' methox group x = 1: 2 2; 3 467 279 Like all alkoxysilanes, trimethylsiloxane is hydrolyzed in the presence of water and cures to form polysiloxanes. which is characterized by high molecular weights (= high degree of polymerization).

During the polymerization, 2 moles of monomers siloxane (1809) consume 1 mole of water (189), releasing 2 moles of methanol (649). Since the sealant during curing, which lasts for up to 24 hours, consumes water, it has the ability to significantly lower the humidity in a closed room, such as the sealed space between the lamp tube 2 and the outer tube 8. In practice, all existing water vapor reacts with siloxane. the monomer when polymerized. As an example, the figures for a 58W lamp with a diameter of 26 mm on the lamp tube 2 and a diameter of 38 mm on the outer tube 8 are given here, which corresponds to 36 mm inner diameter of the latter tube, since the wall thickness is 1 mm.

Ring gap volume 721 cm During manufacture, maximum trapped amount of water (air + 30 ° C, 80% relative humidity atmospheric pressure) 24.3 mg / l = 17.5 mg H O 2 This becomes 0.001 mol of water. 2 x 1.5 siloxane with 60% active substance becomes 1.8 g, which is 0.020 mol. Thus, the security for complete binding of water maximally present in the annular gap 10 is twenty-fold.

In order to ascertain the flammability of the new lamp, comparative tests have been made between ordinary 26 mm fluorescent lamps of 18W, 36W and 58W power and lamps equipped with an outer tube 8 (designated 18W Termo, 36W Termo and 58 W Termo, respectively). The lamps were stored for 24 hours in a freezer, in which the tests were then performed.

The temperature was maintained at each test series at -30 ° C. No metal parts were present in the vicinity of the fluorescent lamps. The tests were done with fl 467 279 using spark plugs that have been in use 8500 ignitions resp. 2000 ignitions, and with new lighters. With 18W tubes, the ignition times were only a few seconds longer than for 18W Termo.

The differences became somewhat clearer when the oldest spark plugs were used.

At 36W Termo, the ignition times were consistently below 5 seconds, while those for 36W were between 8 and 20 seconds, the longest with the oldest spark plugs. 58W could not be lit with the oldest lighters at the test temperature used. When 2000 times used lighters were inserted, only a part of the test lamps lit, and this only after an average of 25 seconds. When using new spark plugs, one lamp lights up after 8 seconds, and all light up during the test sessions of 15 seconds or less. For 58W Termo, the ignitions were noted within 8 seconds, except when the oldest spark plugs were used.

A follow-up test series was performed at a Finnish testing institute, which has the opportunity to perform ignition tests in freezers at -40 ° C. New spark plugs were used, and all ignitions of the tested fluorescent tubes of the Luma Termo 36W / CW-LL took place within 5 seconds.

Figures 2, 3 and 4 show average values of the fluorescent lamps used in the tests with respect to the illuminance at different temperatures. For comparisons, previously documented values for 20W, 40W resp. 65W fluorescent lamp drawn.

For advertising purposes, or otherwise to meet special requests for a certain wavelength composition on the emitted light, the lamp according to the invention can be coated on the inside of the outer tube with substances which filter out unwanted light.

This technique also makes it possible, in the event of special requirements, to further reduce critical UV lines by means of light-absorbing or fluorescent substances. The following substances have proved useful in this regard.

When a red-pink hue is desired, a mixture of inorganic oxides designated (Fe 2 O 3 + 5iO 2 + Al 2 O 3) is used.

For green tinted light use (CuNiZn) 2 (TiAl) O4 and for blue shimmering light Na (SiAl) 02S. The substances are applied to the inside of the outer tube 8 as a suspension and to a dry content between 0.3 and 0.5 mg / cm 2. These paints are burned to the glass, but when using organic dyes, firing above SOOOC temperature can not be applied, so a binder must be used. A suitable one is ammonium polymethyl acrylate.

Claims (7)

H 467 279 Patent claims A tube type low pressure gas discharge lamp for use at low ambient temperatures, comprising a lamp with intermediate gap surrounding glass tube, which extends past the cathode of the lamp and is connected at its ends to its ends, characterized in that the outer glass tube (8) is hermetically connected to the lamp tube (2), and that in the gap (10) between the pipes (2,8), at their ends there are seals (11) of siloxanes, which by hydrolysis in connection with their hardening have absorbed practically all the moisture in the space between the pipes, so that the column (10) has come to contain dry air. Low-pressure gas discharge lamp according to Claim 1, characterized in that the ends of the outer glass tube (8) are received in annular grooves in polymer rings (9) heeled with a press fit on the lamp tube (2), and in the grooves and between the polymer rings (9) and. the lamp tube (2) contains siloxane mass. Low-pressure gas discharge lamp according to Claim 1 or 2, characterized in that the gap (10) between the two glass tubes (2; 8) is filled with dry, dust-free air. Low-pressure gas discharge lamp according to Claim 1 or 2, characterized in that the gap (10) between the two glass tubes (2; 8) contains one or more noble gases. Low-pressure gas discharge lamp according to Claim 4, characterized in that the inside of the surrounding glass tube (B) is coated with a second layer of fluorescent agent. Low-pressure gas discharge lamp according to one of the preceding claims, characterized in that the surrounding tube (8) is coated on the inside of up to half of its mantle surface with a continuous layer of reflective material. 467 279 12 Low-pressure gas discharge lamp according to one of the preceding claims, characterized in that the surrounding tube (8) is coated on the inside in whole or in part with one or more color-changing substances which emit visible light through the inner tube (2).