Low pressure mercury vapor discharge lamp

#1. Field of the Invention

#The present invention relates to a low pressure mercury vapor discharge lamp having a main amalgam for controlling the mercury vapor pressure in the tube of the lamp except for a starting period and having an auxiliary amalgam for controlling the mercury vapor pressure in the tube of the lamp for the starting period. In particular, the invention relates to a low pressure mercury vapor discharge lamp designed to operate in a relatively low to middle tube wall temperature area.

#2. Description of the Related Art

#In the accompanying drawings:

#FIG. 1 is a front sectional view of a fluorescent lamp according to a first embodiment of the present invention;

#FIG. 2 is a graph showing a relation between a mecury vapor pressure and a temperature;

#Referring to the accompanying drawings, embodiments of the present invention will be described. However, in the drawings, the same numerals are applied to similar elements in the drawings, and therefore the detailed descriptions thereof will not be repeated.

#FIG. 1 is a front sectional view of a fluorescent lamp according to a first embodiment of the present invention. The fluorescent lamp has a straight glass main tube 11 and a fluorescent layer 13 coated on the inner surface of the main tube 11. The main tube 11 forms a discharge space therein. The main tube 11 has a pair of stems 15 and 17 with electrodes 19 and 21 and thin tubes 23 and 25. Accordingly, the main tube 11 has a discharge path between both electrodes 19 and 21. The electrodes 19 and 21 are formed in a filament coil type. One of the thin tubes 23 and 25 is used for an exhaust tube. Each electrode 19, 21 is supported by a pair of lead wires 27, 29, respectively. A certain amount of mercury as a discharge gas and also a certain amount of argon gas as a starting gas are filled in the main tube 11. Although the main tube 11 is a straight type as mentioned above, it may be another shape such as a circle shape, U-shape, W-U-shape, H-shape and so on.

#The thin tube 23 has an main amalgam 31 therein. The main amalgam 31 is, for example, bismuth-lead-mercury (Bi-Pb-Hg) amalgam or bismuth-tin-mercury (Bi-Sn-Hg) amalgam whose mercury vapor pressure is not less than a third as much as a mercury vapor pressure of pure mercury in an area between 0.degree. C. and 50.degree. C. Details of the main amalgam 31 are explained later. It is necessary for the main amalgam 31 to have a mercury vapor pressure characteristic close to that of pure mercury in the low and middle temperature area.