Electric lamp and discharge devices: systems – Combined load device or load device temperature modifying... – Discharge device load
Patent
1988-09-19
1990-07-31
Mis, David
Electric lamp and discharge devices: systems
Combined load device or load device temperature modifying...
Discharge device load
315324, H05B 4100, H01J 1734
Patent
active
049452819
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a flat light source.
Flat light sources are known for illuminating for example display panels, the light sources comprising a series of discrete discharge tubes arranged adjacent to one another and energised by an external circuitry incorporating ballast or resistive loads. Light sources of this type are inevitably bulky and require a space behind the display screen which is a of considerable depth. In addition, conventional discharge tubes require a high over-voltage to initiate discharge and the time taken to fully initiate a discharge (the strike time) is considerable. The strike time can be reduced by increasing the over-voltage or using internal or external conductive strips extending along the length of each discharge tube. The known light sources are however difficult to operate over a wide temperature range and if the light output of the light source is to be controllable complex and bulky external dimming circuitry is required. The known light sources are not generally two terminal devices.
Because of the abovementioned disadvantges it has proved difficult to provide a flat light source of acceptable size for use in for example back-lighting liquid crystal displays.
A discharge lamp having a series of parallel elongate discharge compartments is described in Japanese Patent No. JP-A-57-180067. This provides an output equivalent to a series of separate discharge lamps in a compact structure but does not overcome the problems of slow discharge initiation and high minimum overvoltage to initiate a discharge.
Japanese Patent No. JP-A-59-127357 describes a discharge lamp in which a single discharge compartment is defined in a rectangular enclosure by dividing the enclosure into a series of elongate compartments which are interconnected end-to-end. A mechanically strong and compact structure results, but again the problems of high discharge initiation voltages and slow discharge initiation are not overcome.
It is an object of the present invention to provide a flat light source which obviates or mitigates the abovementioned problems.
According to the present invention there is provided a flat light source comprising two sheets of material at least one of which is transparent, the sheets being overlaid one upon the other and sealed together to form a gas tight enclosure which is filled with low pressure gas and within which at least one gas discharge can be initiated between a pair of primary electrodes along a predetermined elongate path, the gas discharge path or paths occupying a plurality of adjacent elongate volumes within the enclosure, characterised in that further electrodes are spaced apart along the length of the or each discharge path, each further electrode being connected to a respective capacitive, resistive or inductive impedance.
Preferably the primary electrodes are exposed within the enclosure and connected to a DC or AC electrical power source. Alternatively however the primary electrodes may be electrically insulated from the enclosure but connected to a high frequency AC electrical power source. An additional resistive, capacitive or inductive load may be placed in series with one or both of the primary electrodes in each pair.
The enclosure may be divided into plurality of parallel channels by spacers positioned between the sheets. Each channel may be associated with a respective pair of primary electrodes, or alternatively the channels may be interconnected end to end to define a single passageway between a single pair of primary electrodes.
The impedances reduce the magnitude of the applied voltage required to initiate a discharge and can be arranged so as to avoid any need for variable loads to assist discharge initiation or dimming of the light output. The impedances also have the important practical functions of stabilising the gas discharges and allowing spacers to be used which do not touch the top and bottom sheets at all points.
Preferably each spacer in section tapers towards the said at least one sheet of material. Alternatively, each space
REFERENCES:
patent: 3047763 (1962-07-01), Inman
Phillips, "Compact Lighting Catalouge", 4/1981, p. 128, Instant Start Lamps.
Mis David
Sidefact Limited
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