Metal halide lamp

DETAILED DESCRIPTION The invention has for its object to provide a lamp which ignites reliably at a low ignition voltage and in which the above disadvantages have been eliminated.
According to the invention, a lamp of the kind mentioned in the opening paragraph is characterized in that the UVE is provided with two internal electrodes between which a glow discharge can extend.
It was surprisingly found that the use of a UVE provided with two internal electrodes substantially counteracts the occurrence of ignition delays at low ignition voltages and in the absence of radioactive ignition means.
In a further advantageous embodiment of the lamp, one of the two internal electrodes is provided with an electrode winding.
A further reduction in the ignition delay is achieved thereby.
A further improvement can be achieved in that one of the internal electrodes is provided with an emitter.
In a further preferred embodiment of the lamp, each of the electrodes of the UVE is provided with an electrode winding with emitter.
A further advantage of the UVE of the lamp according to the invention is that it is also suitable for use in lamps which have a high ignition voltage, for example the known lamp.
This is also true in the case in which the UVE has an electrode winding and is provided with emitter.
A universally applicable UVE is thus realized, which brings with it the possibility of a substantial simplification in lamp manufacture.
Although UVEs with glass or quartz walls are known per se, it is found that their use in a comparable metal halide lamp leads to unacceptable ignition delay times owing to impurities which are inevitably released from the wall.
The ignition delays can only be reduced to practically useful values, it is found, through the use of additional ignition means.
A further practical disadvantage of such UVEs is that their dimensions are considerably larger compared with the very compact construction which is possible for a UVE with a ceramic wall.