Journal of the Illuminating Engineering Institute of Japan

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The doped-tungsten filament for tungsten halogen lamps evolves potassium at such an elevated temperature that they are normally operated.
This potassium plays a role to accelerate initial bulb-blacking in these lamps.
The authers confirmed the above effect through gas analysis and life tests of experimental lamps.
The thermodynamic equilibrium calculations also supported the results of life tests.
These results will contribute to obtain higher luminous efficacy lamps with normal life performance.
The gases evolved from doped tungsten wire during a vacuum heat treatment were analyzed bymeans of a quadrupole mass spectrometer.
Detected gases were K, CO, CO₂, H₂ and hydrocarbons.
When tungsten wire was heated to 2, 900-3, 200°C, CO, CO₂, H₂ decreased and K increased.
Three kinds of tungsten wires different in potassium evolving degree have been compared through life tests of lamps.
Lamps using wire with highest potassium were blackened with only four hours operation at 3100°C.
Equilibrium calculations have been performed at the temperature range 500-4000 K on the heterogeneous systems of tungsten-hydrogen-bromine and of tungsten-hydrogen-potassium-bromine.

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Starting phenomena of metal halide lamps containing iodides of Sc, Th, and Na have been investigated using an analog multiplier element and an oscilloscope.
The arc starting voltage (V_a) between the main electrodes agreed with the ignition voltage (V_sg) between probe and the neighbouring electrode except for the low voltage range.
Relation between energy (E_g) and time (τ) required for the glow-to-arc transition agreed with a theory based upon energy equilibrium on a clean cathode. In the case of the contaminated cathode, the relation shifted to high energy side. The average energy required for clean-up of the cathode was approximately 26 joules corresponding to about 32% of the total energy. The thermal conduction loss of the cathode could not be neglected in these lamps.
Relation between Eg and Va can be written by
E_g=(V_g/RV_a-V²>_g/R) τ
where R is a series resistance and V_g is the average glow discharge voltage. Assuming both V_g and τ are constant, we obtain E_g ∞ V_a. This relation agreed with the experimental results in both AC (60 Hz) and DC operations.

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