Electric lamp and discharge devices – With temperature modifier – For electrode within an envelope
Patent
1987-04-16
1989-03-21
Moore, David K.
Electric lamp and discharge devices
With temperature modifier
For electrode within an envelope
313632, H01J 6106
Patent
active
048146633
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a fluorescent lamp for unipolar mode of operation such as is described in "Lichttechnik", 30th Year, No. 3, 1978, pages 106 to 108.
Such a fluorescent lamp is filled predominantly with mercury vapour, while the inner face of the glass envelope thereof is coated with a fluorescent material. Unipolar mode of operation is a power supply with direct current or with a clocked d.c. voltage, namely with a voltage pulsating with only one polarity, such as a sinusoidal half-wave voltage, a rectangular pulse train etc. A direct current operation, especially of low pressure gas discharge lamps, is such that for physically plausible and experimentally proved reasons--so far as ohmic stabilizing resistances can be avoided--the same leads to a light yield which, as compared to the conventional alternating current operation, is improved by 20% and more.
Yet in the direct current operation mercury ions migrate from the anode to the cathode, which is why the anode region undergoes a mercury impoverishment, whereby the light yield in the anode region is decreased. This phenomenon is also called cataphoresis.
Now in order to reduce cataphoresis, in the case of the fluorescent lamp mentioned in the first paragraphs hereinabove and constructed as a double tube lamp it has been proposed to use a special diaphragm which is permeable to mercury vapor yet which is gas-discharge-tight. However, the use of a suchlike diaphragm and the construction of a double tube lamp represent a considerable expenditure.
From "Technical Newsletter", December 1984, Vol. 6, No. 6, pages 1 and 2 is known a fluorescent lamp the cathode of which is permanently heated in order to provide ideal conditions for igniting the arc discharge and for maintaining the same, as well as a sufficiently high Hg vapour pressure which, in the case of a high switching frequency, is advantageous.
SUMMARY OF THE INVENTION
The problem underlying the invention is to provide a fluorescent lamp for unipolar mode of operation wherein the cataphoresis effect can be decreased to a far-reaching extent by simple means.
The invention is based on the discovery that the cataphoresis can be decreased to a far-reaching extent in that between the cathode and the anode of the fluorescent lamp there is produced a greater temperature gradient. That is why in accordance with the invention the anode is dimensioned so as to have as large an area as possible so that at nominal output the anode should have a small current density and more particularly only up to 10.sup.-5 A/cm.sup.2 whereby achieving that in spite of a sufficient electron beam--stream of electrons--the anode is heated only a little. The anode has a surface which amounts to 60-100% of the maximal cross-sectional area of the discharge envelope, measured vertically to the discharge axis. The arrangement of heat dissipators aids in achieving the desired low temperature of the anode, which moreover prevents the electrode material at the anode side from blackening. The large area anode leads to less anode drop, less anode dissipation and to a higher efficiency.
The small anode current density does also lead to a decrease of the amplitude of the relaxation oscillations in the anode region whereby lesser high frequency distortions occur.
The use of a permanently heated cathode does not only serve for avoiding cataphoresis but it also enhances the controllability of the fluorescent lamp and decreases the cathode drop. Quite generally an external heating of the cathode is compulsorily required for luminosity regulation of the lamp by a variation of the anode current and/or by pulse modulation. Namely in the case of a small effective lamp current this current is not sufficient to heat the cathode to full emission temperature. External cathode heating to a constant emission temperature can take place by direct or alternating current. In a case in which several lamps are operated, the heaters can be connected in parallel and supplied by merely one constant voltage source. Hence it fo
REFERENCES:
patent: 4173730 (1979-11-01), Young et al.
Meyer et al., GTE Technical Newsletter, vol. 6, No. 6, pp. 1 & 2 Dec., 1984.
Eich Armin
Kohler Sigurd
Loy Helmut M.
Bessone Carlo S.
Coleman Edward J.
GTE Products Corporation
Moore David K.
O'Shea Sandra L.
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