EP0123844B1 - Low-voltage halogen projection incandescent lamp - Google Patents

Description

The invention relates to an incandescent lamp according to claim 1. With these highly stressed lamps, in which one moves close to the melting temperature of the tungsten when switched on, the question of the switch-on strength arises, which is defined in that the lamp does not burn when switched on with 110% nominal voltage may be critical in appearance.

In the known lamps of the above-mentioned type, their filament filament, which is designed either as a flat core or round core filament and consists of relatively thick wire and has only a few turns, is wound with a constant pitch. During the switch-on phase, this leads to a temperature distribution along the coil with a temperature maximum of approximately 3550 K in the middle part of the coil, which is already very close to the melting temperature of 3680 K of the tungsten.

Conventional general-purpose incandescent lamps are also known in the prior art which have a coiled filament whose filament pitch at the filament ends is smaller than the filament pitch in the filament center part (cf. DE-A-1 464170 and FR-A-663 276). However, these lamps differ from halogen projection light bulbs both in terms of the gas filling and the lower temperature of the filament.

There is a desire to increase the luminous flux of the halogen projection light bulbs. This is hampered by the fact that during the switch-on phase the temperature value in the central part of the filament equals the melting temperature of the tungsten and the lamp burns out. If, however, the temperature distribution along the filament can be made more uniform, that is to say "leveling _" the temperature maximum to a certain extent, this would result in an increase in the current distance of the filament temperature from the melting temperature of the filament material with a constant luminous flux and opened the transition to higher filament loading than so far, without risk of the filament burning when switched on.

The object of the invention is to provide a low-voltage halogen projection incandescent lamp which has a temperature distribution along the filament which permits the desired increase in luminous flux without problems.

The object is achieved by the features listed in the characterizing part of claim 1.

• Figur 1 die Niedervolt-Halogen-Projektionsglühlampe schematisch im Schnitt,
• Figur 2 eine Flachkernwendel in Seitenansicht,
• Figur 3 eine Flachkernwendel mit den verschiedenen Steigungsabschnitten,
• Figur 4 den Temperaturverlauf längs der Wendel.

The lamp is described in more detail below. Show from the figures

• FIG. 1 shows the low-voltage halogen projection incandescent lamp schematically in section,
• FIG. 2 shows a flat core helix in a side view,
• FIG. 3 shows a flat core helix with the different slope sections,
• Figure 4 shows the temperature profile along the coil.

The low-voltage halogen projection light bulb (FIG. 1) has a bulb 1 made of quartz or Vycor®, is filled with inert gas with halogen addition, has a pump tip 2 at one end and is closed at the other end by squeezing. A coiled filament 3 made of tungsten (FIGS. 2, 3) is carried by tungsten current feeds 4, which are welded to molybdenum foils 5 and connected to external current feed pins 6 via these. The filament filament 3 can be designed as a flat core or round core filament. The slope of the filament filament 3 is dimensioned such that it is smaller at the filament ends than in the filament middle part. While the helical pitch of the helix is a _E ends E _{1 'E} 2 in the range 1.2 <a _e <1.7, the value of the helix pitch of the helical central portion a _M M is taken from the range 2.2 1.4 <a ≤ _M. The helix pitch can increase either gradually or continuously from the helix ends to the helix center. A along the filament more uniform temperature profile (curve 1) compared to the temperature profile at a constant helical pitch, the result (curve 2), as Figure 4 shows, the abscissa _n the number of turns W and the ordinate represents the flare temperature T.

The deviation - maximum temperature to minimum temperature along the filament - is approximately AT <150 K in contrast to previously AT = 250 K, which means that the luminous flux is increased by about 10% (hatched area in Figure 4) while maintaining the switch-on strength criterion results.

Claims (2)

1. An incandescent lamp comprising a coiled luminous element made of tungsten, whose coil pitch a_E at the coil ends (E₁, E₂) is smaller than the coil pitch (a_M) in the region of the coil centre (M), characterised in that the incandescent lamp is a low voltage halogen projection incandescent lamp whose luminous element, which is subject to a high thermal load, has a temperature which is close to the melting temperature of tungsten during the switch-on phase and whose coil pitch relative to the coil diameter lies within the range 1.2 ≤ a_E < 1.7 at the coil ends (E₁, E₂) and within the range 1.4 < a_M < 2.2 at the coil centre (M).

2. An incandescent lamp as claimed in claim 1, characterised in that the temperature maximum at the coil centre during the switch-on phase is 3,550 K.

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