Patent Publication Number: US-7592742-B2

Title: Fluorescent lamp, bulb-shaped fluorescent lamp, and lighting apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This is a Continuation Application of PCT Application No. PCT/JP2004/000832, filed Jan. 29, 2004, which was published under PCT Article 21(2) in Japanese. 
   This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-038746, filed Feb. 17, 2003, the entire contents of which are incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a fluorescent lamp, a bulb-shaped fluorescent lamp, and a lighting apparatus having a fluorescent lamp or a bulb-shaped fluorescent lamp. 
   2. Description of the Related Art 
   In recent years, lighting apparatuses having a fluorescent lamp have become smaller, and their output has increased. In small and high-output lighting apparatuses, however, the light output of the fluorescent lamp tends to decrease. The smaller the lighting apparatus and the greater its output, the higher the temperature in the light-emitting tube of the fluorescent lamp becomes, with the result that the mercury-vapor pressure in the light-emitting tube is likely to increase. In order to suppress the excessive rise of the mercury-vapor pressure, fluorescent lamps for use in places where their intra-tube temperature may rise have a light-emitting tube filled with a main amalgam. 
   In the fluorescent lamp provided with the main amalgam, its light-emitting efficiency increases because the main amalgam suppresses an excessive rise of mercury-vapor pressure, as described above. However, a long time is required after a fluorescent lamp of this type is turned on, until the lamp starts emitting a predetermined luminous flux, i.e., the fluorescent exhibits a poor flux-startup characteristic. This is because the main amalgam suppresses the mercury-vapor pressure not only while the lamp is turned on, but also while the intra-tube temperature is as low as room temperature as occurring before the lamp is turned on, as compared to the fluorescent lamps filled with pure mercury. The fluorescent lamp having main amalgam emits a weak luminous flux immediately after it is turned on, due to the insufficient mercury-vapor pressure, though the luminous flux gradually increases as the intra-tube temperature rises, raising the mercury-vapor pressure in the sealed glass tube. 
   For these reasons, the fluorescent lamp having the main amalgam is provided with an auxiliary amalgam at a portion near the electrode, where the temperature can readily rise when the lamp is turned on. This adds a pressure to the mercury-vapor pressure in the light-emitting tube immediately after the lamp is turned on, thereby improving the flux-startup characteristics. 
   As auxiliary amalgam with which fluorescent lamps are provided, one is known that comprises a base made of stainless steel on which indium (In) is plated. However, this auxiliary amalgam is high in adsorption power for mercury, lowering the mercury-vapor pressure even more, while the lamp is turned off. 
   Further, as an auxiliary amalgam with which fluorescent lamps are provided, one is known which comprises a base on which gold (Au) is plated, as disclosed in Jpn. Pat. Appln. KOKAI Publication 2001-84956. Gold does not adsorb mercury excessively while the lamp remains off, and thus can maintain the mercury-vapor pressure relatively high at room temperature. It follows that a fluorescent lamp with auxiliary amalgam that comprises a base on which gold is plated can attain a large output immediately after it is turned on. Gold has a high melting point and hardly evaporates, and is hardly oxidized in the heating step during the manufacture of the fluorescent lamp. In view of this, gold is desirable for providing an auxiliary amalgam. 
   In the fluorescent lamp disclosed in Jpn. Pat. Appln. KOKAI Publication 2001-84956, however, the auxiliary amalgam has but a short lifetime. That is, the lamp obtains only a short period of time during which a flux-startup characteristic is improved. This is because gold is likely to diffuse into the base made of stainless steel (solid phase diffusion). Note that the gold layer plated on the stainless-steel base makes up for the mercury-vapor pressure in the fluorescent lamp immediately after the lamp is turned on. The gold therefore diffuses into the stainless-steel base. When the gold on the base decreases in amount, the auxiliary amalgam can no longer serve to provide a good flux-startup characteristic. 
   The technique described in Jpn. Pat. Appln. KOKAI Publication 2001-84956 may be employed to maintain a good flux-startup characteristic for a long time. In this case, the auxiliary amalgam must be plated with a thick gold layer. Gold is very expensive material. The thicker the gold layer, the higher the manufacturing cost of the fluorescent lamp. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a fluorescent lamp, a bulb-shaped fluorescent lamp, and a lighting apparatus, which exhibits good flux-startup characteristic for a long time. 
   In an aspect of this disclosure, a fluorescent lamp described in claim  1  comprises a light-emitting tube and an amalgam contained in the light-emitting tube. The amalgam has a base, a metal layer provided on the base, and a diffusion-inhibiting layer provided between the base and the metal layer to inhibit the diffusion of the metal from the metal layer into the base. 
   Unless otherwise specified, the definitions and technical meanings of the terms are as follows. 
   The light-emitting tube can be made of glass, or ceramic or the like that can form a light-transmitting sealed envelope. The glass may be lead glass, which has a low softening point and can easily be heat-processed, lead-free glass, which is environmentally friendly, or the like. 
   The light-emitting tube may be a straight one, an annular one and a bent one. Alternatively, it may comprise plurality of bent tubes connected together, end to end, with communicating tubes so as to form at least one electrical discharge path. 
   When the light-emitting tube has a bent tube, the bent tube can be U-shaped. The U-shaped, bent tube may be formed by heat melting the middle part of a straight tubular member (e.g., a straight glass tube) and then bending the tube at the middle part. Otherwise, it may be prepared by subjecting a straight tubular member to a molding process. The term “U-shaped, bent tube” means a tube having an electrical discharge path that is so folded that the discharge path is turned back. Therefore, the U-shaped, bent tube is not limited to one having a curved part or a circular part. Rather, it may be bent at an obtuse or acute angle. In other words, “U-shaped, bent tube” means a bulb consisting of straight tubular parts that are connected, end-to-end, so that the discharge circuit may be bent. The bent tube may be composed of two substantially parallel straight tubular parts that are connected by a connecting tube prepared by blown-off technique. Alternatively, the bent tube may be a spiral one. 
   The fluorescent lamp may be a general-type one that has a pair of electrodes respectively located at the ends of the discharge path provided in the light-emitting tube. Otherwise, the fluorescent lamp may be a so-called electrode-less lamp, which has no electrodes. If the fluorescent lamp has two electrodes located at the ends of the discharge path formed in the light-emitting tube, respectively, the electrodes may be hot cathodes made of filaments, ceramic electrodes coated with electron-emitting material, or cold cathode made of nickel or the like. 
   A phosphor layer is formed directly or indirectly on the inner surface of the light-emitting tube. The phosphor layer may be made of rare-earth-metal oxide phosphor, halophosphate phosphor, or the like. Nonetheless, the material of the phosphor layer is not limited to these. To enhance the light-emitting efficiency of the lamp, it is desirable to use three-wavelength emission phosphor that is a mixture of three phosphors that emits red light, blue light and green light, respectively. 
   The light-emitting tube is filled with a discharge medium. The discharge medium may be mercury, inert gas such as argon, neon, krypton or xenon, or a mixture gas of mercury and inert gas. The medium is not limited to these, nevertheless. 
   The amalgam contained in the light-emitting tube well serves as so-called “auxiliary amalgam.” Auxiliary amalgam improves the flux-startup characteristic of the lamp. (It can shorten the time within which the luminous reaches a predetermined intensity after the lamp is turned on.) In addition to the auxiliary amalgam, so-called “main amalgam” is provided in the light-emitting tube, thereby filling mercury vapor in the tube. Note that the main amalgam provides an appropriate mercury-vapor pressure when the lamp is turned on. 
   The main amalgam may not be used at all. If this is the case, liquid mercury, a mercury pellet (Zn—Hg alloy), GEMEDIS (trade name, manufactured by Saes Getters, Inc.), or the like may be provided in the light-emitting tube, thereby filling the light-emitting tube with mercury. In this case, too, auxiliary amalgam can be used to improve the flux-startup characteristic of the fluorescent lamp. 
   Main amalgam, if provided in the light-emitting tube, is preferably one that can control the mercury-vapor pressure to an appropriate value when the lamp attains while operating in the stable state. The metal composition and mercury content of the main amalgam determine the mercury-vapor characteristic of the main amalgam. Metals desired as metal components of the main amalgam are bismuth (Bi), lead (Pb), Tin (Sn), indium (In), and the like. Thus, the main amalgam is, for example, bismuth (Bi)-Tin (Sn)-Mercury (Hg), bismuth (Bi)-Tin (Sn)-lead (Pb)-mercury (Hg), bismuth (Bi)-lead (Pb)-Indium (In)-mercury (Hg), or zinc (Zn)-mercury (Hg), or the like. Nonetheless, the main amalgam is not limited to these. 
   To make the auxiliary amalgam to perform it function appropriately, it is desirable to place it at a position where the temperature can easily raise, for example in the vicinity of the electrode. In a fluorescent lamp having an electrode, it is desired that the auxiliary amalgam be, for example, welded to the inner lead line that supports the electrode. In a fluorescent lamp comprising bent tubes connected together, the auxiliary amalgam may be positioned in one of the bent tube and at the midpoint of the discharge path. In an electrode-less lamp, the auxiliary amalgam should better be provided at a position in the discharge space, where the current density is high. 
   Iron (Fe), nickel (Ni), chromium (Cr), manganese (Mn), copper (Cu), niobium (Nb), molybdenum (Mo), zirconium (Zr), titanium (Ti), aluminum (Al), tungsten (W), carbon (C), or alloy containing at least two of these elements excels in heat resistance and is, therefore, suitable as the material of the base of the auxiliary amalgam. 
   Among the alloys containing at least two of the elements mentioned is stainless steel. The base made of stainless steel is very resistant to heat and easy to process, and is inexpensive. In view of these points, stainless steel is fit for the material of the base. Preferably, the base is shaped like a plate or a mesh. Otherwise, it may be shaped like a wire or a hollow cylinder. Nonetheless, the shape of the base is not limited to these. 
   It is desired that the metal layer of the auxiliary amalgam be made of metal that hardly adsorbs, to excess, the mercury in the light-emitting tube while the fluorescent lamp is operating. Therefore, the inventors hereof studied the metal layer of the auxiliary amalgam, in order to improve the flux-startup characteristic of the lamp. 
   First, the inventors prepared the following auxiliary amalgams. The base was made of stainless steel (i.e., alloy of Fe, Ni and Cr), and have a size of 2 mm×7 mm and a thickness of 40 μm. Then, a layer of different metal was formed on the base by means of electroplating. 
   Gold, silver, palladium, platinum, lead, tin, zinc and bismuth were used as materials of the metal layer. Different types of auxiliary amalgam, which have the same base as described above and layers of gold, silver, palladium, titanium, tin, zinc and bismuth, respectively, were used in bulb-shaped, 13 W-class fluorescent lamps that correspond to 60 W incandescent lamps. 
   On the other hand, a bulb-shaped fluorescent lamp provided with an auxiliary amalgam made of the abovementioned base on which indium was plated was prepared as Comparative Example 8; a bulb-shaped fluorescent lamp comprising no auxiliary amalgam was prepared as Comparative Example 9; and a bulb-shaped fluorescent lamp provided with an auxiliary amalgam made of abovementioned base on which nickel was plated was prepare as Comparative Example 10. These bulb-shaped fluorescent lamps were those of consumptive power of 13 W, corresponding to 60 W of incandescent lamp. 
   All bulb-shaped fluorescent lamps thus prepared were tested to determine the relation between the light-emitting time and relative light output. 
   As  FIG. 27  shows, the bulb-shaped fluorescent lamps having a gold layer, a silver layer, a lead layer, a tin layer and a zinc layer, respectively, emitted light instantaneously when they were turned on, whose intensity was 30% to 40% of the intensity attained when the lamps operate in the stable state. The luminous flux well increased thereafter. Though not shown in  FIG. 27 , the bulb-shaped fluorescent lamps that had a palladium layer, a platinum layer and a bismuth layer, respectively, exhibited similar characteristics. 
   By contrast, the bulb-shaped fluorescent lamp according to Comparative Example 8 emitted light instantaneously when it was turned on, whose intensity was about 10% of the intensity attained when the lamp stably operated, though the luminous flux increased well. The bulb-shaped fluorescent lamp according to Comparative Example 9 emitted light whose intensity was about 40% instantaneously when it was turned on, but the luminous flux did not increased well thereafter. About three minutes had elapsed until it the light intensity increased to 80%. The bulb-shaped fluorescent lamp according to Comparative Example 10 exhibited characteristics similar to those of the lamp according to Comparative Example 9. 
   These characteristics can be explained as follows. In the bulb-shaped fluorescent lamp according to Comparative Example 9, which had no auxiliary amalgam, the mercury-vapor pressure in the light-emitting tube does not excessively falls while the lamp remains off. However, the liquid mercury existing near the discharge path that is the main heat-generating part is insufficient in amount. Inevitably, the luminous flux did not so increase as desired. 
   Nickel scarcely adsorbs mercury. Hence, what has been the of the Comparative Example 9 can hold true for the bulb-shaped fluorescent lamp according to Comparative Example 10 that uses nickel as material of the metal layer of the auxiliary amalgam. 
   Indium can adsorb a very large amount of mercury. Thus, in the bulb-shaped fluorescent lamp according to Comparative Example 8 that uses indium for the metal layer of the auxiliary amalgam, the mercury-vapor pressure in the light-emitting tube falls to excess while the lamp remains off. Consequently, the light the lamp emits instantaneously when turned on is not sufficiently intense. 
   Gold, silver, palladium, platinum, lead, tin, zinc and bismuth adsorb mercury not so little as nickel and no so much as indium. Hence, the bulb-shaped fluorescent lamp that contains auxiliary amalgam having a metal layer of gold, silver, palladium, platinum, lead, tin, zinc or bismuth can emit intense light from the start, and the luminous flux increases well. 
   The above mentioned fluorescent lamps, which will further be described later, should better have a metal layer that contains at least one element selected from the group consisting of gold (Au), silver (Ag), palladium (Pd), platinum (Pt), lead (Pb), tin (Sn), zinc (Zn) and bismuth (Bi). 
   Preferably, the metal layer consists mainly of one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth, or the metal layer consists mainly of alloy that contains at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. 
   The clause “the metal layer consists mainly of one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth” means a metal layer that contains at least 50% by mass of one of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. That is, the metal layer may of course be made of substantially only gold, silver, palladium, platinum, lead, tin, zinc or bismuth. Alternatively, the metal layer may be made of a mixture (alloy) that contains at least 50% by mass of one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. The phrase “substantially only” means that the metal layer may contain a trace of impurities. More preferably, the metal layer contains at least 90% by mass of any one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. 
   The clause “the metal layer consists mainly of alloy that contains at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth” means that the metal layer contains at least 50% by mass of alloy of at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. That is, the metal layer may contain any elements other than those specified, provided that at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth account for at least 50% by mass of the metal layer. Preferably, the metal layer contains at least 90% by mass of alloy of at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. 
   The metal layer may be one that contains not only gold, silver, palladium, platinum, lead, tin, zinc and bismuth but also a small amount (about 0.1 to 8% by mass) of nickel (Ni), copper (Cu), cobalt (Co), iron (Fe) or the like. Alternatively, the metal layer may be one that consists mainly of gold or silver and contains a small amount (about 0.1 to 8% by mass) of nickel, cobalt, platinum, palladium, copper, iron and the like. Particularly, any alloy prepared by adding nickel and cobalt in small amount to gold is called “hard gold,” which is harder than pure gold. A metal layer made of this alloy is desirable, because it is hardly worn or peeled off during the manufacture of the fluorescent lamp. The metal layer can be provided on the base by means of electroplating or vapor deposition. 
   The metal layer that contains at least one element selected from the group consisting of gold (Au), silver (Ag), palladium (Pd), platinum (Pt), lead (Pb), tin (Sn), zinc (Zn) and bismuth (Bi) may have compositions exemplified below. Nevertheless, the metal layer is not limited to these examples.
         (a) Pb: 50% by mass; Bi: 50% by mass   (b) Au: 92% by mass; Ag: 8% by mass   (c) Au: 75% by mass; Ag: 25% by mass   (d) Au: 10% by mass; Ag: 90% by mass   (e) Au: 98% by mass; Ag: 1% by mass; Ni, Co, Pt, Pd, Cu and Fe: 1% by mass   (f) Au: 92% by mass; Ag: 7% by mass; Ni, Co, Pt, Pd, Cu and Fe: 1% by mass   (g) Au: 70% by weight; Ag: 29% by mass; Ni, Co, Pt, Pd, Cu and Fe: 1% by mass   (h) Au: 70% by weight; Ag: 23% by mass; Ni, Co, Pt, Pd, Cu and Fe: 7% by mass   (i) Au: 40% by mass; Ag: 59% by mass; Ni, Co, Pt, Pd, Cu and Fe: 1% by mass   (j) Au: 40% by mass; Ag: 53% by mass; Ni, Co, Pt, Pd, Cu and Fe: 7% by mass   (k) Bi: 60% by mass; Pb: 20% by mass; Sn: 10% by mass;   Cu: 9% by mass; Ni, Co, Pt, Pd and Fe: 15% by mass   (l) Au: 70% by mass; Ag: 20% by mass; Cu: 9% by mass;   Ni, Co, Pt, Pd and Fe: 1% by mass   (m) Au: 70% by mass; Ag: 20% by mass; Bi: 9% by mass;   Ni, Co, Pt, Pd, Cu and Fe: 1% by mass   (n) Au: 70% by mass; Ag: 20% by mass; Pb: 9% by mass;   Ni, Co, Pt, P-d, Cu and Fe: 1% by mass   (o) Au: 70% by mass; Ag: 20% by mass; Sn: 9% by mass;   Ni, Co, Pt, Pd, Cu and Fe: 1% by mass       

   Preferably, the diffusion-inhibiting layer is made of material into which metal particles hardly diffuse from the metal layer. In the above-mentioned lamp, it is therefore desired that the diffusion-inhibiting layer should contain at least one element selected from the group consisting of nickel (Ni), chromium (Cr), molybdenum (Mo) and tungsten (W). 
   Gold, silver, palladium, platinum, lead, tin, zinc bismuth and the like are, among others, hardly diffuse into the elements (chromium, molybdenum and tungsten) belonging to Group VI of the Periodic Table and nickel. Hence, metal particles will scarcely diffuse (solid phase diffusion) from the metal layer into the base if a diffusion-inhibiting layer containing one or more of nickel, chromium, molybdenum and tungsten is interposed between the base and the metal layer. This can lengthen the lifetime of the amalgam. 
   It is more desired that the diffusion-inhibiting layer be made mainly of least one element selected from the group consisting of nickel, chromium, molybdenum and tungsten, or be made mainly of alloy containing at least two elements selected from the group consisting of nickel, chromium, molybdenum and tungsten. 
   The clause “the diffusion-inhibiting layer be made mainly of one element selected from the group consisting of nickel, chromium, molybdenum and tungsten” means a diffusion-inhibiting layer that contains at least 50% by mass of at least one element selected from the group consisting of nickel, chromium, molybdenum and tungsten. That is, the diffusion-inhibiting layer may of course be made of substantially only nickel, chromium, molybdenum or tungsten. Alternatively, the diffusion-inhibiting layer may be made of a mixture (alloy) that contains at least 50% by mass of one element selected from the group consisting of nickel, chromium, molybdenum and tungsten. The phrase “substantially only” means that the diffusion-inhibiting layer may contain a trace of impurities. More preferably, the diffusion-inhibiting layer contains at least 90% by mass of any one element selected from the group consisting of nickel, chromium, molybdenum and tungsten. 
   The phrase “made mainly of alloy containing at least two elements selected from the group consisting of nickel, chromium, molybdenum and tungsten” means a diffusion-inhibiting layer containing at least 50% by mass of alloy that contains at least two elements selected from the group consisting of nickel, chromium, molybdenum and tungsten. Namely, the diffusion-inhibiting layer may be made of a mixture (alloy) that contains not only at least two elements selected from the group consisting of nickel, chromium, molybdenum and tungsten, but also other elements, if the at least two elements account for at least 50% by mass. More preferably, the diffusion-inhibiting layer contains at least 90% by mass of at least two elements selected from the group consisting of nickel, chromium, molybdenum and tungsten. 
   The following simple method can demonstrate that the metal layer of the auxiliary amalgam hardly gets thinner. 
   First, two types of auxiliary amalgams are prepared. One type comprises a base (e.g., one made of stainless steel) and a metal layer (e.g., gold layer) formed on the base hand having thickness of about 0.5 μm. The other type comprises a base (e.g., one made of stainless steel), a diffusion-inhibiting layer (e.g., nickel layer) formed on the base hand having thickness of about 0.5 μm, and a metal layer (e.g., gold layer) formed on the diffusion-inhibiting layer and having thickness of about 0.5 μm. The auxiliary amalgams, thus prepared, are heated at about 500° C. in a vacuum furnace for about 1 hour. Then, the amalgam having no diffusion-inhibiting layer loses the luster of gold and reveals the luster of stainless steel, whereas the amalgam having a diffusion-inhibiting layer keeps presenting the luster of gold. This simple method shows that metal hardly diffuses from the metal layer into the base, owning to the diffusion-inhibiting layer interposed between the base and the metal layer. 
   To make the lamp retain good the flux-startup characteristic for a long time, it is desired that the diffusion-inhibiting layer of the amalgam should have a thickness of 0.01 μm or more and 5 μm or less. The diffusion-inhibiting layer must be 0.01 μm or more thick, because some metal particles in the metal layer diffuse into the diffusion-inhibiting layer, too. If the thickness of the diffusion-inhibiting layer is less than 0.01 μm, metal particles (crystals of metal) will diffuse from the metal layer into the diffusion-inhibiting layer, soon reaching the base. If the thickness of the diffusion-inhibiting layer is less than 0.01 μm, it will have pinholes, through which metal particles may pass into the base. In order to reduce the material cost, to decrease the amount of amalgam required and to improve the process efficiency, it is desired that the diffusion-inhibiting layer be about 5 μm or less thick, preferably about 0.03 to 2 μm thick. 
   After formed on the diffusion-inhibiting layer that is provided on the base, the metal layer may be hardly provided on the diffusion-inhibiting layer (that is, the metal layer may not be laid on the diffusion-inhibiting layer). If this is the case, a peeling-inhibiting layer made mainly of nickel should better be provided between the base and the metal layer, more precisely between the diffusion-inhibiting layer and the metal layer. The diffusion-inhibiting layer may not be firmly provided on the base (that is, the diffusion-inhibiting layer may not be firmly laid on the base). In this case, too, it is desirable to provide a peeling-inhibiting layer made mainly of nickel, between the base and the metal layer, more precisely between the base and the diffusion-inhibiting layer. 
   The phrase “peeling-inhibiting layer made mainly of nickel” means a peeling-inhibiting layer that contains at least 50% by mass of nickel. Preferably, the peeling-inhibiting layer contains at least 90% by mass of nickel. 
   In the above-mentioned fluorescent lamps, a diffusion-inhibiting layer is provided between the metal layer and the base to inhibit metal from diffusing into the base from the metal layer. Thus, metal particles (crystals of metal) in the metal layer can hardly diffuse into the diffusion-inhibiting layer or the base. This lengthens the lifetime of the amalgam (i.e., the period for which the flux-startup characteristic remains good thanks to the amalgam). Moreover, the metal layer can be thinner than in the conventional lamp because metal particles scarcely diffuse from the metal layer into the base. The material cost of the metal layer can therefore decrease. 
   Nickel, chromium, molybdenum and tungsten are more expensive than stainless steel. Hence, any amalgam that has a diffusion-inhibiting layer containing at least one element selected from the group consisting of nickel, chromium, molybdenum and tungsten and being interposed between the metal layer and the base made of stainless steel can be manufactured at a lower cost than the amalgam whose base contains at least one element selected from the group consisting of nickel, chromium, molybdenum and tungsten. Such amalgam is used in the above-mentioned fluorescent lamp. 
   The above-mentioned fluorescent lamp is advantageous in that the material cost of amalgam is low and in that the weight of amalgam is small. In addition, the diffusion-inhibiting layer can easily formed on the base, without having pinholes. 
   In the above-mentioned fluorescent lamp, the metal layer is inhibited from peeling from the base, and the diffusion-inhibiting layer and the metal layer can be easily formed, one upon the other. 
   The above-mentioned fluorescent lamp comprises a light-emitting tube and amalgam contained in the light-emitting tube. The amalgam has a base and a metal layer. The base contains at least one element selected from the group consisting of chromium, molybdenum and tungsten. The metal layer contains at least one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth and is provided on the base. 
   Preferably, the metal layer be made of metal would not excessively adsorb mercury in the light-emitting tube while the fluorescent lamp remains off. Hence, it is desired that the metal layer contain at least one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. 
   More preferably, the metal layer is made mainly of at least one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth, or made mainly of alloy that contains at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. The phrase “the metal layer is made mainly of at least one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth,” and the phrase “made mainly of alloy that contains at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth” of the same meaning as described above. 
   As pointed out already, gold, silver, palladium, platinum, lead, tin, zinc bismuth, and the like are, among others, hardly diffuse into the elements of Group VI (chromium, molybdenum and tungsten) in the periodic table. Therefore, metal particles will scarcely diffuse from the metal layer into the base if the base is made of material that contains at least one element selected from the group consisting of chromium, molybdenum and tungsten. This can lengthen the lifetime of the amalgam. 
   It is more desirable that the base be made mainly of one element selected from the group consisting of chromium, molybdenum and tungsten, or made mainly of alloy that contains at least two elements selected from the group consisting of chromium, molybdenum and tungsten. 
   The clause “the base made mainly of one element selected from the group consisting of chromium, molybdenum and tungsten” means a base that contains at least 50% by mass of at least one element selected from the group consisting of chromium, molybdenum and tungsten. Namely, the base may of course be made of substantially only chromium, molybdenum or tungsten. Alternatively, the base may be made of a mixture (alloy) that contains at least 50% by mass of one element selected from the group consisting of chromium, molybdenum and tungsten. The phrase “substantially only” means that the metal layer may contain a trace of impurities. The phrase “substantially only” means that the metal layer may contain a trace of impurities. Preferably, the base contains at least 90% by mass of any one element selected from the group consisting of chromium, molybdenum and tungsten. 
   The clause “the base made mainly of alloy that contains at least two elements selected from the group consisting of chromium, molybdenum and tungsten” means a base that contains at least 50% by mass of alloy containing at least two elements selected from the group consisting of chromium, molybdenum and tungsten. Namely, the base may be made of a mixture (alloy) that contains other elements, if the at least two elements account for at least 50% by mass. Preferably, the base contains at least 90% by mass of at least two elements selected from the group consisting of nickel, chromium, molybdenum and tungsten. 
   The base may be made mainly of molybdenum. That is, the base may of course be made of molybdenum only. Alternatively, the base may be made of molybdenum doped with yttrium (Y). 
   The metal layer may likely to peel off (that is, the metal layer may not be firmly adhered to the base). If this is the case, it is desirable to provide a peeling-inhibiting layer made mainly of nickel, between the base and the metal layer. The phrase “peeling-inhibiting layer made mainly of nickel” is of the same meaning as specified above. 
   In the above-mentioned fluorescent lamp, metal particles hardly diffuse from the metal layer into the base even if the metal layer is made mainly one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc, lead and bismuth. This is because the base contains at least one element selected from the group consisting of chromium, molybdenum and tungsten. Hence, it is possible to lengthen the lifetime of the amalgam (i.e., the period for which the flux-startup characteristic remains good thanks to the amalgam). Moreover, the metal layer can be thinner than in the conventional lamp because metal particles scarcely diffuse from the metal layer into the base. The material cost of the metal layer can therefore decrease. 
   The above-mentioned fluorescent lamp comprises a light-emitting tube and amalgam contained in the light-emitting tube. The amalgam has a base and a metal layer provided on the base. The crystals that constitute the metal layer are porous. 
   The clause “The crystals that constitute the metal layer are porous” means such a state as is illustrated in  FIGS. 8 and 9 . 
   Such a metal layer can be formed by electroplating the base with metal that forms a layer on the base if the potential between the electrodes is lower than usual and is raised upon lapse of a predetermined time. 
   The speed with which the crystals grow does not depend on the potential between the electrodes. Nonetheless, the higher the potential, the faster the nuclei of crystal grow. Hence, if the potential between the electrodes is lower than usual, the crystals grow faster than the nuclei. As a result, the crystallization is promoted. The potential between the electrodes is raised after the crystals have grown to some extent. Then, the speed with which the nuclei grow increases, and the ion concentration falls at the surface of the cathode. When the ion concentration falls at the surface of the cathode, discharging can hardly be achieved at the entire surface. Only partial discharging occurs, making the surface gradually uneven. Eventually, the surface has projections and depressions. The ion concentration at the projections is higher at any other regions. Discharging is concentrated at the projections. The growth of crystal is therefore promoted at the projections and thereabout. As a result, crystals are deposited, forming such a porous layer as shown in  FIGS. 8 and 9 . This type of deposition is called “dendrite deposition.” If the ordinary deposition, not dendrite deposition, takes place, such crystals as shown in  FIGS. 10 and 11  will be formed. 
   Preferably, the metal layer is one to which mercury in the light-emitting tube scarcely is excessively adsorbed during turning-off of the fluorescent lamp. In view of this, it is desired that the metal layer contain at least one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. 
   More preferably, the metal layer is made mainly of one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth, or made mainly of alloy containing at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. The clause “the metal layer is made mainly of one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth,” and the phrase “made mainly of alloy containing at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth” are of the same meaning as mentioned above. 
   The metal layer may not be provided on the base (that is, the metal layer may not be laid on the base). In this case, it is desirable to provide a peeling-inhibiting layer made mainly of nickel, between the base and the metal layer. The phrase “peeling-inhibiting layer made mainly of nickel” is of the same meaning as specified above. 
   In the above-mentioned fluorescent lamp, it is desired that the crystals that form the metal layer be used at a filling ratio of 10% to 90% as defined in claim  7 . 
   The term “filling ratio” is the ratio of the volume that the metal particles actually occupy to the apparent volume that the metal layer has. 
   Assume that a layer of gold (Au) having an area S [cm 2 ] and a thickness of t [cm] is formed on a flat substrate. The apparent volume of the layer is S×t. Gold has specific density d of 19.32 [g/cm 3 ]. If the filling ratio is 100%, gold will stick to the substrate in an amount of d×S×t [g]. In the porous metal layer shown in  FIGS. 8 and 9 , spaces exits between the crystals. Thus, gold sticks to the substrate in an amount that is smaller than d×S×t [g]. The porous metal layer shown in  FIGS. 8 and 9  (formed by dendrite deposition) has a filling ratio of about 80%. By contrast, such a metal layer as shown in  FIGS. 10 and 11  (formed through the ordinary deposition) has a filling ratio of about 100%. 
   If the metal has a filling ratio of less than 10%, the metal layer will likely peel from the base. If the metal layer has a filling ratio exceeding 90%, the area at which the metal particles contact the base will be so large that the metal particles can easily diffuse into the base. 
   In the above-mentioned fluorescent lamp, the area at which the metal particles (crystals of the metal) contact the base can be reduced. Thus, the metal particles hardly diffuse into the base. This can lengthen the lifetime of the amalgam (i.e., the period for which the flux-startup characteristic remains good thanks to the amalgam). In addition, the metal layer can be thinner than is possible hitherto, because the metal particles hardly diffuse into the base. This helps to decrease the material cost of the metal layer. 
   The above-mentioned fluorescent lamp comprises a light-emitting tube, and amalgam contained in the tube and having a base and a metal layer provided on the base. The crystals that constitute the metal layer have a size that satisfies at least one of the following three conditions. First, randomly selected regions of the surface of the metal layer have an arithmetic mean roughness that exceeds 0.02 μm. Second, these regions of the surface of the metal layer have a maximum roughness-height that exceeds 0.3 μm. Third, the surface of the metal layer has a ten-point average roughness that exceeds 0.2 μm. 
   In the above-mentioned fluorescent lamp, the crystals that constitute the metal layer have a size that satisfies at least one of the following three conditions. First, randomly selected regions of the surface of the metal layer have an arithmetic mean roughness that exceeds 0.02 μm. Second, these regions of the surface of the metal layer have a maximum height roughness that exceeds 0.3 μm. Third, the surface of the metal layer has a ten-point average roughness that exceeds 0.2 μm. 
   The arithmetic mean roughness Ra, the maximum roughness-height Ry, and the ten-point average roughness Rz are defined at JIS B 0601, Japanese Industrial Standards. They are parameters, each indicating the surface roughness of some parts, selected at random, of a metal layer to be examined. Generally, an object has no uniform surface roughness; the surface roughness differs, from one region to another. Therefore, the metal layer need not have a uniform surface roughness, only if it meets at least one of the above-mentioned three conditions, i.e., arithmetic mean roughness Ra&gt;0.02 μm, maximum roughness-height Ry of roughness&gt;0.3 μm, and ten-point average roughness Rz&gt;0.2 μm. 
   For the above-mentioned fluorescent lamp, the size of the crystals in the metal layer (i.e., crystals constituting the metal layer) is defined in terms of the surface roughness that the metal layer has. This is because the surface of the metal layer becomes rougher as the crystals in the metal layer grow larger. 
   A metal layer of this type can be formed by electroplating the base with metal, by maintaining a relatively low potential between the electrodes for a predetermined time and then raising the potential upon lapse of the predetermined time, as in forming the metal layer of the amalgam which the fluorescent lamp has. The metal layer thus formed comprises crystals that are shaped like needles or grains, and therefore has a surface more rough than ordinary gloss plating. 
   It is desired that the metal layer be made of metal hardly adsorbs mercury in the light-emitting tube while the fluorescent lamp remains off. Thus, in the above-mentioned fluorescent lamp too, the metal layer should better contain at least one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth, as in the fluorescent lamp. 
   More preferably, the metal layer is made mainly of one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth, or made mainly of alloy that contains at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth. The clause “the metal layer is made mainly of one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth” and the phrase “made mainly of alloy that contains at least two elements selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth” are of the same meaning as specified above. 
   The metal layer may hardly be provided on the base (that is, the metal layer may not be laid on the base). In this case, it is desirable to provide a peeling-inhibiting layer made mainly of nickel, between the base and the metal layer, as in the fluorescent lamp. The phrase “peeling-inhibiting layer made mainly of nickel” is of the same meaning as specified above. 
   In the above-mentioned fluorescent lamp, the metal crystals in the metal layer satisfy at least one of the following three conditions. The first condition is that randomly selected regions of the surface of the metal layer have an arithmetic mean roughness Ra that exceeds 0.02 μm. The second condition is that the metal layer has a maximum roughness-height Ry that exceeds 0.3 μm. The third condition is that the surface of the metal layer has a ten-point average roughness that exceeds 0.2 μm. Hence, the crystals hardly diffuse from the metal layer into the base. This lengthens the lifetime of the amalgam (i.e., the period for which the flux-startup characteristic remains good thanks to the amalgam). Further, the metal layer can be thinner than is possible hitherto, because the crystals hardly diffuse from the metal layer into the base. This helps to decrease the material cost of the metal layer. 
   The above-mentioned fluorescent lamp can include a metal layer having a thickness of 0.05 μm to 5 μm. 
   The thinner the metal layer, the better the flux-startup characteristic. It was found that lamps exhibit good flux-startup characteristic if they have amalgam having a metal layer that is 5 μm or less thick. It was found that the lamps maintain good flux-startup characteristic to the end of their lifetime, even if the metal diffuses a little into the base, if the metal layer has a thickness of 0.05 μm or more. 
   To enhance the flux-startup characteristic, to reduce the material cost and to decrease the amount of amalgam required, it is desired that the metal layer be as thin as possible. If the metal layer is too thin, however, it will be difficult to form and process it. Hence, it is preferred that the metal layer be about 0.5 μm thick in order to enhance the flux-startup characteristic, to reduce the material cost and to decrease the amount of amalgam required, as well as to improve processability of the metal layer. 
   In the above-mentioned fluorescent lamp, the metal layer is 0.05 μm to 5 μm thick. This suppresses the material cost and the amount of amalgam used. Moreover, the lamp can maintain good flux-startup characteristic to the end of its lifetime. 
   In the above-mentioned lamp, the base is 10 μm to 60 μm thick. 
   To reduce the material cost and decrease the amount of amalgam used, it is desired that the base be 60 μm or less thick. To be sufficiently strong and heat-resistant, the base should be 10 μm or more thick. Preferably, the base is about 40 μm±10 μm. 
   In the fluorescent lamp, wherein the base is 10 μm to 60 μm thick, the amalgam can be sufficiently strong and heat-resistant. In addition, the material cost can be reduced and the amalgam can be used in a reduced amount. Moreover, the base can be easily processed. In the fluorescent lamp, the amalgam can release mercury upon receiving heat generated immediately after the lamp is turned on. 
   In this lamp, a peeling-inhibiting layer made mainly of nickel is provided between the base and the metal layer. 
   The phrase “made mainly of nickel” is of the same meaning as described above. To reduce the material cost, decrease the amount of amalgam required and prevent the metal layer from coming off the base during. the manufacture of the lamp, the peeling-inhibiting layer should be 5 μm or less think, preferably about 0.01 μm thick. 
   Generally, metal can be well laid on the outer surface, which is made mainly of nickel. That is, since the metal layer can be easily laid on the above-mentioned outer surface and the metal layer hardly peels from it, by providing a peeling-inhibiting layer made mainly of nickel between the metal layer and the base or between the metal layer and the diffusion-inhibiting layer, the metal layer can be stably provided on the outer surface of the base through the peeling-inhibiting layer. This make it possible to prevent the peeling of the metal layer during the manufacturing of the fluorescent lamp, and the lamp can maintain improved flux-startup characteristic for a long time. 
   The above-mentioned lamp further comprises main amalgam that produces a mercury-vapor pressure of 0.04 Pa or more at 25° C. 
   To improve the flux-startup characteristic even more, the mercury-vapor pressure should be high while the lamp remains off. It is therefore desirable that the main amalgam should bring forth a mercury-vapor pressure of 0.04 Pa or more at 25° C. The mercury-vapor pressure that pure mercury generates at 25° C. is about 0.24 Pa. Hence, the mercury-vapor pressure at 25° C. would not exceed 0.24 Pa. More preferably, the main amalgam should produce a mercury-vapor pressure 0.15 Pa or more at 25° C. and of 1.0 Pa to 2.0 Pa at 50° C. to 70° C. As a main amalgam having such characteristics, for example, one prepared by adding 4 to 25% by mass of mercury to an alloy having 50 to 60% by mass of bismuth (Bi) and 35 to 50% by mass of tin (Sn) may be mentioned. Nevertheless, the main amalgam is not limited to this one. 
   Since the above-mentioned fluorescent lamp comprises main amalgam that brings forth a mercury-vapor pressure of 0.04 Pa or more at 25° C., the fluorescent lamp can have its flux-startup characteristic improved even more. Further, the mercury-vapor pressure in the light-emitting tube can be controlled to an appropriate value while the lamp is operating in the stable state. 
   The bulb-shaped fluorescent lamp comprises a fluorescent lamp of the type described herein, a lamp-driving device, and a cover. The lamp-driving device has a substrate and electronic components mounted on the substrate, and is configured to output high-frequency power to the fluorescent lamp. The cover contains the lamp-driving device, and has a cap at one end and a holding part at the other end. The holding part holds the fluorescent lamp. 
   Since the bulb-shaped fluorescent lamp comprises a fluorescent lamp of the type described herein, the bulb-shaped fluorescent lamp can maintain a good flux-startup characteristic for a long time. Additionally, it can be manufactured at a lower cost than the conventional bulb-shaped fluorescent lamps. 
   A lighting apparatus hereinafter comprises a fluorescent lamp and a main unit to which the fluorescent lamp is attached. The fluorescent lamp is of the type described herein. 
   Another lighting apparatus hereinafter comprises a bulb-shaped fluorescent lamp and a main unit to which the fluorescent lamp is attached. The bulb-shaped fluorescent lamp is of the type described herein. 
   The main unit can be a known-type one, such as a bulb-burying unit or a direct-holding unit designed for, for example, down lights. Alternatively, the main unit may be the main unit of a light apparatus already installed. The above-mentioned lighting apparatus may have a small main unit or a large-output, lamp-driving device. In this case, they operate well if the temperature can easily be raised in the light-emitting tube of the fluorescent lamp. 
   The above-mentioned lighting apparatus preferably has a fluorescent lamp that can maintain a good flux-startup characteristic for a long time. 
   The above-mentioned lighting apparatus can have a bulb-shaped fluorescent lamp that can maintain a good flux-startup characteristic for a long time. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a partly sectional side view showing a bulb-shaped fluorescent lamp that comprises a fluorescent lamp according to a first embodiment of this invention; 
       FIG. 2  is an expansion plan view of the light-emitting tube provided in the fluorescent lamp according to the first embodiment; 
       FIG. 3  is a plan view showing the light-emitting tube of the fluorescent lamp according to the first embodiment, as viewed from the cap, while the tube being held by a holder; 
       FIG. 4  is a partly magnified sectional view depicting the first auxiliary amalgam provided in the fluorescent lamp according to the first embodiment; 
       FIG. 5  is a sectional view showing the first auxiliary amalgam provided in the fluorescent lamp according to the first embodiment; 
       FIG. 6  is a sectional view showing another type of auxiliary amalgam that may be provided in the fluorescent lamp according to the first embodiment; 
       FIG. 7  is a sectional view showing still another type of auxiliary amalgam that may be provided in the fluorescent lamp according to the first embodiment; 
       FIG. 8  is a photograph of the metal layer of the auxiliary amalgam shown in  FIG. 4 , magnified 3,000 times; 
       FIG. 9  is a photograph of the metal layer of the auxiliary amalgam shown in  FIG. 4 , magnified 10,000 times; 
       FIG. 10  is a photograph of a conventional metal layer formed by electroplating, magnified 3,000 times; 
       FIG. 11  is a photograph of the conventional metal layer formed by electroplating, magnified 10,000 times; 
       FIG. 12  is a graph representing the relation between the temperature of the first auxiliary amalgam and the detected amount of hydrogen, observed in the fluorescent lamp according to the first embodiment, and the relation between the temperature of the amalgam and the detected amount of hydrogen, observed in Comparative Example 1; 
       FIG. 13  is a partly magnified sectional view illustrating a second auxiliary amalgam that may replace the first auxiliary amalgam in the fluorescent lamp according to the first embodiment; 
       FIG. 14  is a partly magnified sectional view illustrating a third auxiliary amalgam that may replace the first auxiliary amalgam in the fluorescent lamp according to the first embodiment; 
       FIG. 15  is a diagram representing the flux-startup characteristic that a fluorescent lamp having the first auxiliary amalgam exhibits immediately after it is turned on; 
       FIG. 16  is a diagram representing the flux-startup characteristic that a fluorescent lamp having the second auxiliary amalgam exhibits immediately after it is turned on; 
       FIG. 17  is a diagram representing the flux-startup characteristic that a fluorescent lamp having the third auxiliary amalgam exhibits immediately after it is turned on; 
       FIG. 18  is a diagram illustrating the flux-startup characteristic that the fluorescent lamp according to Comparative Example 2 exhibits immediately after it is turned on; 
       FIG. 19  is a table showing the relative luminous fluxes that three fluorescent lamps having the first, second and third auxiliary amalgam, respectively, emit five seconds after they are turned on, and showing the relative luminous flux that the fluorescent lamp of Comparative Example 2 emits five seconds after it is turned on; 
       FIG. 20  is a magnified sectional view of a part of the fourth auxiliary amalgam used, in place of the first auxiliary amalgam, in the fluorescent lamp according to the first embodiment; 
       FIG. 21  is a diagram, explaining how to measure the surface area of the light-emitting tube that is provided in the fluorescent lamp according to a second embodiment; 
       FIG. 22  is a graph illustrating how the luminous flux emitted by the fluorescent lamp according to the second embodiment and those emitted by the fluorescent lamps of Comparative Examples 3, 4, 5 and 6 changes with time; 
       FIG. 23  is a sectional view depicting a fluorescent lamp according to a third embodiment of the present invention; 
       FIG. 24  is a graph illustrating how the luminous flux that the fluorescent lamp according to the third embodiment emits changes with time, and how the luminous flux that a fluorescent lamp of Comparative Example 7 emits changes with time; 
       FIG. 25  is a side view showing a fluorescent lamp according to a fourth embodiment of this invention; 
       FIG. 26  is a partly sectional, side view showing a lighting apparatus that incorporates the bulb-shaped fluorescent lamp according to the first embodiment; and 
       FIG. 27  is a graph representing the relationship between the flux-startup characteristics of bulb-shaped fluorescent lamps having auxiliary-amalgam metal layers of gold, silver, lead, tin and zinc, respectively, and time, and between the flux-startup characteristic of a convention bulb-shaped fluorescent lamp and time. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The first embodiment of this invention will be described, with reference to  FIGS. 1 to 12 . This embodiment is applied to a fluorescent lamp and a bulb-shaped fluorescent lamp that comprises this fluorescent lamp. 
   As  FIG. 1  shows, the bulb-shaped fluorescent lamp  10  comprises a fluorescent lamp  12 , a cover  40 , a lamp-driving device  50 , and a globe  60 . The cover  40  comprises a cover body  41 , a cap  42 , and a holder  43 . The cap  42  is provided at one end of the cover body  41 . The holder  43  is provided at the other end of the cover body  41  and used as a holding part. 
   The cover  40  and the globe  60  constitute an envelope  11 . The envelope  11  is formed, having a size similar to the standard size of bulbs for general lighting use, such as incandescent lamps that have the rated power of 40 W. The fluorescent lamp  10  has height H 1  of about 110 to 125 mm, including that of the cap  42 , and diameter D 1  of about 50 to 60 mm, which is the diameter of the globe  60 . The cover  40  has diameter D 2  of about 40 mm. The phrase “bulbs for general lighting use” means the bulbs defined at JIS C 7501. The envelope  11  contains the fluorescent lamp  12  and the lamp-driving device  50 . 
   The fluorescent lamp  12  comprises a light-emitting tube  20 , main amalgam  26   a,  and auxiliary amalgam  30   a.  The light-emitting tube  20  has an alumina (Al 2 O 3 ) protection film (not shown) and a phosphor layer (not shown). The protection film is formed on inner surface of the tube  20 . The phosphor layer is formed on the protection film and made of three-wave emitting phosphor, or a mixture of three phosphors that emit, for example, red light, blue light and green light, respectively. The red-emitting phosphor is, for example, europium-activated yttrium oxide phosphor (Y 2 O 2 :Eu 3+ ), which has peak wavelength of about 610 nm. The blue-emitting phosphor is, for example, europium-activated barium aluminate-magnesium phosphor (BaMg 2 Al 16 O 27 :Eu 3+ ), which has peak wavelength of about 450 nm. The green-emitting phosphor is, for example, cerium and tellurium-activated lanthanum phosphate light-emitting substance ((La, Ce, Tb)PO 4 ), which has peak wavelength of about 540 nm. The three-wave emitting phosphor may be adjusted to emit light of desired chromaticity by mixing not only the red-, blue- and green-emitting phosphors specified above, but also a phosphor that emits light of a color other than the red, blue and green. The phosphor layer is provided in the light-emitting tube  20  by means of coating, after bent tubes  21   a,    21   b  and  21   c  are prepared as will be described later. 
   As  FIG. 2  shows, the light-emitting tube  20  comprises a plurality of bent tubes that are substantially identical in shape. For example, the tube  20  comprises three bent tubes  21   a,    21   b  and  21   c.  The bent tubes  21   a,    21   b  and  21   c  are arranged at prescribed positions and coupled, one to the next one, by connecting tubes  22 . Thus, coupled, the bent tubes constitute one discharge path. The three bent tubes  21   a,    21   b  and  21   c  are U-shaped. Each bent tube has a pair of straight tubes  23  and a curved part  24 . The straight tubes  23  are substantially parallel. The curved part  24  connects the straight tubes  23 , end to end. As  FIG. 3  depicts, the bent tubes  21   a,    21   b  and  21   c  are so arranged that the straight tubes  23  lie on a circle and that three curved parts  24  define a triangle. Thus, the bent tubes form a triple-U structure. The light-emitting tube  20  may comprise four bent tubes. In this case, the curved portions of the bent tubes define a square. 
   The bent tubes  21   a,    21   b  and  21   c  are made of lead-free glass. Each bent tube has an outside diameter of about 11 mm and an inside diameter of about 9.4 mm, and a wall thickness of about 0.8 mm. It has been formed by smoothly bending the middle part of a straight tube about 110 to 130 mm long. The curved part  24  of each bent tube can be formed into a desired shape by heating and bending the middle part of a straight tube, then inserting the bent part in a mold, and finally pressurizing the inside of the bent part. Thus, the curved part  24  can have any desired shape that complies with the shape of the mold. 
   Preferably, the bent tubes  21   a,    21   b  and  21   c  have an outside diameter of 9.0 to 13.0 mm and a wall thickness of 0.5 to 1.5 mm. It is desired that the length of discharge path in the light-emitting tube  20  should be 250 to 500 mm and a lamp-input power is 8 to 25 W. 
   That is, the light-emitting tube  20  comprising, as bent tubes  21   a,    21   b  and  21   c,  glass tubes having an outside diameter of 9.0 to 13.0 mm and a wall thickness of 0.5 to 1.5 mm can constitute the bulb-shaped fluorescent lamp  10  having a shape similar to that of incandescent lamps, if designed to have a discharge path of 250 to 500 mm long and a lamp-input power of 8 to 25 W. The inventors hereof conducted a study to find a turning-on region in which the lamp efficiency of the light-emitting tube  20  can be improved if the discharge path is lengthened. The study shows that the lamp efficiency can be remarkably improved if the discharge path is 250 to 500 mm long and if the lamp-input power ranges from 8 W to 25 W. 
   The bent tubes  21   a,    21   b  and  21   c  are liable to deform due to the heating during the manufacture of the fluorescent lamp  10  or to the temperature difference between the turned-off period and the turned-on period. The mechanical strength of the connecting tubes  22  decreases, greatly depending on the outside diameter and wall thickness of the glass tubes used as connecting tubes  22 . If the bent tubes  21   a,    21   b  and  21   c  have an outside diameter less than 9.0 mm or a wall thickness less than 0.5 mm, the light-emitting tube  20  will likely be broken, due to a cause other than the deformation of the bent tubes  21   a,    21   b  and  21   c . Therefore, it is not desired that the bend tubes  21   a,    21   b  and  31   c  have an outside diameter less than 9.0 mm or a wall thickness less than 0.5 mm. If the bent tubes  21   a,    21   b  and  21   c  have an outside diameter exceeding 13 mm, or a wall thickness exceeding 1.5 mm, the connecting tubes  22  will acquire sufficient mechanical strength. 
   The glass used as material of the bent tubes  21   a,    21   b  and  21   c  contains a large amount of sodium component (Na 2 O), i.e., alkali component. The e sodium component deposits at the heating step in forming the bent tubes  21   a,    21   b  and  21   c.  It reacts with the phosphor, possibly degrading the phosphor. In view of this, it is desired that the bent tubes  21   a,    21   b  and  21   c  be made of material that contains essentially no lead and contains a limited amount of the sodium component. If made of such material, the bent tubes will little influence the environment and scarcely degrade the phosphor. Hence, the fluorescent lamp  12  can have its flux-startup characteristic improved. 
   The glass used as material of the bent tubes  21   a,    21   b  and  21   c  has a specific composition. The glass is composed of, in weight ratio, 60 to 75% of SiO 2 , 1 to 5% of Al 2 O 3 , 1 to 5% of Li 2 O, 5 to 10% of Na 2 O, 1 to 10% of K 2 O, 0.5 to 5% of CaO, 0.5 to 5% of MgO, 0.5 to 5% of SrO, and 0.5 to 7% of BaO. In the glass, SrO/BaO≧1.5, and MgO+BaO≦SrO. Made of the glass having this composition, the bent tubes  21   a,    21   b  and  21   c  more improved the flux-startup characteristic of the light emitting tube  20  than bent tubes made of leaded glass, though it remains unclear why. 
   The bent tubes  21   a,    21   b  and  21   c  are sealed, each at one end by pinch sealing or the like. The bent tubes are connected at the other end to thin pipes  25 , by pinch sealing or the like. The thin pipes  25  have an outside diameter of 2 to 5 mm and an inside diameter of 1.2 to 4.2 mm. They protrude from one end of the light-emitting tube  20 . The thin pipe  25  on the bent tube  21   b  located in the middle is a dummy pipe. The thin pipe  25  on the bent tube  21   c  located at one side serves to evacuate the light-emitting tube  20 . The thin pipe  25  on the bent tube  21   a  located on the other side contains the main amalgam  26   a.    
   The main amalgam  26   a  comprises, for example, a base made of 50 to 60% by mass of bismuth (Bi) and 35 to 50% by mass of tin (Sn), to which 12 to 25% by mass of mercury is added. 
   A filament coil  27  used as an electrode is sealed and supported by a pair of wells  28   c  in that end part of the bent tube  21   c  (located at one end of the light-emitting tube  20 ), which is coupled to no other bent tube. Similarly, a filament coil  27  used as an electrode is sealed and supported by a pair of wells  28   a  in that end part of the bent tube  21   a  (located at the other end of the light-emitting tube  20 ), which is coupled to no other bent tube. The wells  28   a  and  28   c  are connected to four wire  29  extending from the light-emitting tube  20 , by Dumet wire (not shown) sealed by means of pinch sealing without a mount, or the like. Two pairs of wires, or four wires  29 , are electrically connected to the lamp-driving device  50 . 
   A plurality of auxiliary amalgam masses, for example three auxiliary amalgam masses  30   a,  are provided in the vicinity of the filament coils  27 . More correctly, one of the three auxiliary amalgam masses  30   a  is attached to one of the wells  28   a  provided in the bent tube  21   a.  Another of the three auxiliary amalgam mass  30   a  is attached to one of the wells  28   c  provided in the bent tube  21   c.  The remaining auxiliary amalgam mass  30   a  is provided in the middle bent tube  21   b.  This auxiliary amalgam mass  30   a  is attached to a well  28   b  sealed by pinch sealing or the like and is located in the discharge path. 
   As  FIG. 4  shows, each auxiliary amalgam  30   a  has a base  31   a,  a nickel layer  33  and a metal layer  32   a.  More precisely, a nickel layer  33  made mainly of nickel is formed on the base  31   a,  to a thickness of about 0.5 μm. The metal layer  32   a  is made of substantially only gold (Au) and formed on the nickel layer  33 . 
   The base  31   a  is a plate of stainless steel (iron-nickel-chromium alloy), which is, for example, 2 mm wide, 7 mm long and 40 μm thick. The nickel layer  33  functions as a peeling-inhibiting layer that inhibits the metal layer  32   a  from peeling from the base  31   a.  The layer  33  functions as diffusion-inhibiting layer, too, which inhibits metal from diffusing from the layer  32   a  into the base  31   a.  The nickel layer  33  is provided on the base  31   a  by means of, for example, electroplating. 
   To be more specific, the metal layer  32   a  comprises at least 98% by mass of gold and contains, as impurities, nickel, cobalt and the like. The mean thickness of the metal layer  32   a  is 1.0 μm. The metal layer  32   a  is formed on the nickel layer  33 , through dendrite deposition of substantially pure gold, which is accomplished, for example, by a plating method using an alkaline bath. Some surface regions of the metal layer  32   a,  selected at random, were removed and examined for surface roughness. These surface regions had arithmetic mean roughness Ra of 0.047 μm, maximum roughness-height Ry of 0.762 μm, and ten-point average roughness Rz of 0.538 μm. 
     FIGS. 8 and 9  show a central surface part of the metal layer  32   a,  photographed at different magnifications. As seen from  FIGS. 8 and 9 , the crystals constituting the metal layer  32   a  are porous. The crystals have grown larger than those that form the conventional plated metal layer (see  FIGS. 10 and 11 ). The crystals forming the metal layer  32   a  exist at a filling ratio of about 80%. 
   The metal layer  32   a  may be provided on only one surface of the base  31   a,  as illustrated in  FIG. 5 . Alternatively, it may be formed on both surfaces of the base  31   a,  as depicted in  FIG. 6 . Otherwise, it may cover all surfaces of the base  31   a,  as shown in  FIG. 7 . The auxiliary amalgam  30   a  may be prepared by forming a metal layer  32   a  on a stainless-steel strip of the prescribed size (about 2 mm×about 7 mm, in this embodiment). Instead, it may be made by first forming a metal layer  32   a  on a large stainless-steel plate and then cutting the plate into pieces of a prescribed size (about 2 mm×about 7 mm, in this embodiment). 
   As is known in the art, the metal layer easily absorbs hydrogen if formed by electroplating. The reason why so is thought to be as follows. 
   Electroplating is a process of forming a metal layer on a base that acts cathode, by virtue of electrolysis that proceeds in a bath of the aqueous solution containing a specific substance. To form a gold (Au) layer on a stainless-steel base, for example, an aqueous solution containing gold cyanide or the like is used, and the stainless-steel base is used as cathode. As a result, a gold layer is formed on the stainless-steel base. 
   In electroplating, side reactions usually accompanies the main reaction, i.e., the electrolysis of the substance. More precisely, the side reactions are the oxidation of water (generation of oxygen at the anode) and the reduction of water (generation of hydrogen at the cathode). Both chemical reactions (i.e., oxidation and reduction) take place in the aqueous solution. The hydrogen generated at the cathode is easily absorbed into the metal layer that is being formed by electroplating. 
   Electroplating using an acidic bath is believed to generate more hydrogen in the side reaction than electroplating that uses a neutral bath or an alkaline bath. 
   In any electroplating using a neutral or alkaline bath, hydrogen is generated in a side reaction, as the electrolysis of water proceeds as indicated by the following formula (1):
 
2H 2 O+2 e→ 2OH − +H 2 ↑  (1)
 
   Any acidic bath contains more hydrogen ions (H + ) than the neutral or alkaline bath. Hence, in electroplating using an acidic bath, a side reaction of the following formula (2) accompanies the main reaction, i.e., the electrolysis of water, indicated by the formula (2)
 
2H + +2 e →H 2 ↑  (2)
 
   This is why any metal layer formed by electroplating using an acidic bath is believed to absorb more hydrogen than any metal layer formed by electroplating using a neutral or alkaline bath. 
   When hydrogen gas mingles into the discharge medium filled in the light-emitting tube of a fluorescent lamp, it may raise the starting voltage, decrease the ultraviolet-ray output or degrade the characteristic of the fluorescent lamp. It is therefore desirable to inhibit hydrogen from entering the light-emitting tube as much as possible. When the auxiliary amalgam prepared by applying electroplating is inserted into the light-emitting tube, however, hydrogen inevitably enters the light-emitting tube together with the auxiliary amalgam. The hydrogen absorbed in the metal layer of the auxiliary amalgam gradually emanates into the light-emitting tube as the amalgam is heated while the fluorescent lamp remains on or as the metal layer undergoes sputtering due to electric discharge. 
   It is therefore desired that the auxiliary amalgam should absorb hydrogen as little as possible. Hydrogen may be removed from the auxiliary amalgam by heating the auxiliary amalgam. In view of this, auxiliary amalgam from which hydrogen can be removed at low temperatures is preferable. 
   The amount of hydrogen that the auxiliary amalgam  30   a  has absorbed was measured. Also measured was the amount of hydrogen absorbed into auxiliary amalgam according to Comparative Example 1, which will be described below. 
   As described above, the auxiliary amalgam  30   a  comprises a base  31   a,  a nickel layer  33  formed on the base  31   a,  and a metal layer  32   a  made of dendrite Au formed on the nickel layer  33  by dendrite electroplating. The metal layer  32   a  was prepared by electroplating using an alkaline bath as described above. Some surface region of the metal layer  32   a,  selected at random, had arithmetic mean roughness Ra of 0.047 μm, maximum roughness-height Ry of 0.762 μm, and ten-point average roughness Rz of 0.538 μm, as specified above. 
   The auxiliary amalgam according to Comparative Example 1 comprises a base, a nickel layer formed on the base, and a lustrous metal layer, or lustrous Au layer, formed by ordinary electroplating. The base is a stainless-steel plate that is 2 mm wide, 7 mm long and 40 μm thick, like the base  31   a.  The nickel layer is 0.5 m thick, like the nickel layer  33 . Like the metal layer  32   a,  the metal layer comprises at least 98% by mass of gold and contains, as impurities, nickel, cobalt and the like. Like the metal layer  32   a,  it has a mean thickness of 1.0 μm. This metal layer was made by electroplating using an acidic bath. Some surface region of this metal layer, selected at random, had arithmetic mean roughness Ra of 0.01 μm, maximum roughness-height Ry of 0.285 μm, and ten-point average roughness Rz of 0.01 μm. 
   The amount of hydrogen absorbed was measured by a quadrupole mass spectrometry. Quadrupole mass spectrometry can determine the components of gas released from a sample heated in vacuum and the composition of the gas.  FIG. 12  shows the results of the quadrupole mass spectrometry. More correctly,  FIG. 12  shows the relation between the temperature of the auxiliary amalgam  30   a  and the detected amount of hydrogen released from the amalgam  30   a,  and the relation between the temperature of the auxiliary amalgam of Comparative Example 1 and the detected amount of hydrogen released from this auxiliary amalgam. 
   As seen from  FIG. 12 , the maximum amount of hydrogen detected of the auxiliary amalgam  30   a  that has the metal layer  32   a  formed by dendrite electroplating was smaller than the maximum amount of hydrogen detected of the auxiliary amalgam that has a metal layer formed by the ordinary electroplating. Thus, the total amount of hydrogen detected of the auxiliary amalgam  30   a  was smaller than the total amount of hydrogen detected of the auxiliary amalgam according to Comparative Example 1. The analysis of the results of quadrupole mass spectrometry teaches that the amount of hydrogen that the auxiliary amalgam  30   a  absorbs was about half the amount of hydrogen that the auxiliary amalgam of Comparative Example 1 absorbs. Hence, the auxiliary amalgam  30   a  having the metal layer  32   a  formed by dendrite electroplating (using an alkaline bath) can be said to absorb less hydrogen than any auxiliary amalgam that has been formed by the ordinary electroplating (using an acidic bath). 
   As  FIG. 12  shows, more hydrogen was detected at low temperatures from the auxiliary amalgam  30   a  having the metal layer  32   a  formed by dendrite electroplating, than from the auxiliary amalgam having a metal layer formed by the ordinary electroplating. In other words, the auxiliary amalgam  30   a  having the metal layer  32   a  formed by dendrite electroplating can remove more hydrogen than any auxiliary amalgam that has a metal layer formed by the ordinary electroplating, when subjected to a low-temperature heating process. 
   Hence, the auxiliary amalgam  30   a  can remove more hydrogen than the conventional auxiliary amalgam in the heating step performed in the manufacture of the fluorescent lamp  12 . The fluorescent lamp  12 , which has this auxiliary amalgam  30   a,  can operate at a lower starting voltage than any fluorescent lamp that comprises the conventional auxiliary amalgam. Moreover, the auxiliary amalgam  30   a  serves to suppress the decrease of the ultraviolet-ray output of the fluorescent lamp  12 . 
   The light-emitting tube  20  is formed such that the bent tubes  21   a,    21   b  and  21   c  have height H 2  of 50 to 60 mm, the tube  20  has a discharge path is 200 to 350 mm long, and the bent tubes  21   a,    21   b  and  21   c  have a maximum width D 3  of 32 to 43 mm in their juxtaposed direction (see  FIG. 1 ). The light-emitting tube  20  is filled with argon gas at a filling pressure of 400 to 800 Pa, constituting at least 99% of all gas in the tube  20 . 
   The bulb-shaped fluorescent lamp  10  will be further described, referring the cap  42  as the upper end, and the globe  60  as the lower end. 
   The cover  40  comprises the cover body  41 , the cap  42 , and the holder  43 , and has an accommodating space therein for accommodating the lamp-driving device  50 . The cap  42  is provided at one end (upper end) of the cover body  41 . The holder  43  holds the fluorescent lamp  12  that is provided at the other end (lower end) of the cover body  41 . It is desired that the cover body  41  be separated from the holder  43 . Nonetheless, the cover body  41  and the holder  43  may be integrally formed. 
   The cover body  41  is made of heat-resistant synthetic resin such as polybutylene terephthalate (PBT). As  FIG. 1  depicts, the cover body  41  is shaped like a hollow cylinder, flaring from one end (upper end) to the other end (lower end). The cap  42 , such as an E26-type cap, is mounted on one end of the cover body  41 . The cap  42  is secured to the cover body  41  with adhesive or by means of caulking. The cap  42  need not be directly attached to the cover body  41 . It may be indirectly coupled to the cover body  41  or may constitute an integral part of the cover body  41 . 
   The holder  43 , which holds the lamp-driving device as well as the light-emitting tube, is secured to the other end of the cover body  41 . The holder  43  has a port through which an end part of the light-emitting tube  20  can pass. The light-emitting tube  20  is attached to the holder  43 , which is secured to the cover body  41  and covers the opening of the cover body  41 . Coupling means (not shown) couples the substrate  51  of the lamp-driving device  50  to the holder  43 . 
   As shown in  FIG. 1 , the lamp-driving device  50  has a plurality of electronic components  52 , in addition to the substrate  51 . The substrate  51  is arranged, perpendicular to the axis X passing the center  01  of the cap  42 . The electronic components  52  are mounted on the substrate  51 . The lamp-driving device  50  is an inverter circuit (high-frequency lamp-driving device). The lamp-driving device  50  is provided in the cover  40  such that the substrate  51  is secured and most of the electronic components  52  are arranged at the cap  42 . The lamp-driving device  50  is electrically connected to the cap  42  and the fluorescent lamp  12 . Receiving power through the cap  42 , the device  50  operates, supplying high-frequency power to the filament coil  27  that acts as an electrode and making the fluorescent lamp  12  emit light. The lamp-driving device  50  has a smoothing electrolytic capacitor, like most types of lamp-driving devices. Nonetheless, the device  50  may not have such capacitors. 
   The substrate  51  is shaped like a disc. It has a diameter (i.e., maximum size) that is at most 1.2 times the maximum width of the light-emitting tube  20 . Most of the electronic components  52 , including the smoothing electrolytic capacitor, inductors, a transformer, resistors and film capacitors, are mounted on one surface (upper surface) of the substrate  51 , which lies in the cap  42 . The other electronic components, including field-effect transistors (FETs), rectifying diodes (RECs) and chip resistors, are mounted on the other surface (lower surface) of the substrate  51 , which lies in the light-emitting tube  20 . 
   The globe  60  is either transparent or opaque, capable of transmitting light or dispersing light. The globe  60  is made of glass or synthetic resin. It is similar in shape to ordinary glass bulbs and has a curved surface. The globe  60  has an opening at one end (upper end). The globe  60  contains the fluorescent lamp  12  and connected, at the opening, to the other end of the cover  40 . The globe  60  may have a diffusion film or the like, to enhance the uniformity of luminance. 
   The lamp-driving device  50  is configured to make the fluorescent lamp  12  emit light, by supplying lamp power of 7 to 15 W and setting the current density (current per unit area) to 3 to 5 mA/mm 2  in the light-emitting tube  20 . The bulb-shaped fluorescent lamp  10  is of a rated input power of 8 W, and high-frequency power of 7 W is supplied to the light-emitting tube  20 . The lamp current is 120 mA, and the lamp voltage is 80V. As the light-emitting tube  20  emits light, the total luminous flux of the bulb-shaped fluorescent lamp  10  amounts to about 480 lm. 
   Other two types of auxiliary amalgam than can be used in the fluorescent lamp  12 , in place of the first auxiliary amalgam  30   a,  will be described with reference to  FIGS. 13 and 14 . 
   The auxiliary amalgam  30   b  shown in  FIG. 13  (hereinafter, referred to as second auxiliary amalgam) comprises a base  31   a,  a metal layer  32   b  and a nickel layer  33  provided between the base  31   a  and the metal layer  32   b.  The base  31   a,  metal layer  32   b  and nickel layer  33  are identical to those of the first auxiliary amalgam  30   a  in terms of material, thickness and the like. The metal layer  32   b  has an arithmetic mean roughness Ra of 0.01 μm, a maximum roughness-height Ry of 0.285 μm, and ten-point average roughness Rz of 0.155 μm. The metal layer  32   b  may be formed by, for example, ordinary bright electroplating. 
   The auxiliary amalgam  30   c  shown in  FIG. 14  (hereinafter, referred to as third auxiliary amalgam) comprises a base  31   b,  which is a plate having a thickness of 40 μm and a size of 2×7 mm and made mainly of molybdenum. A peeling-inhibiting layer  35  having a thickness of about 0.01 μm and made mainly of nickel is formed on the base  31   b.  The peeling-inhibiting layer  35  is provided to lay the metal layer  32   c  firmly on the base  31   b.  It is not indispensable. On the peeling-inhibiting layer  35 , the metal layer  32   c  is formed. The metal layer  32   c  is identical in material to the first amalgam  30   a  described above. The metal layer  32   c  has a thickness of 0.5 μm. The metal layer  32   c  has an arithmetic mean roughness Ra of 0.01 μm, a maximum roughness-height Ry of 0.285 μm, and ten-point average roughness Rz of 0.01 μm. The metal layer  32   c  may be formed by, for example, ordinary bright electroplating. 
   Bulb-shaped fluorescent lamps  10  comprising the above-mentioned fluorescent lamps  12  provided with the first to third auxiliary amalgams  30   a,    30   b  and  30   c,  respectively, were tested to determine their flux-startup characteristics. The results were as follows. 
   The bulb-shaped fluorescent lamp  10  having the first auxiliary amalgam  30   a  was measured for its flux-startup characteristic (i.e., the luminous flux change with time with respect to the value, set at 100%, after the time when the lamp  10  starts operating in the stable state). As seen from  FIGS. 15 and 19 , the relative luminous flux (flux-startup characteristic) was 56.6% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp  10  had been turned on for 0 hours in total. The relative luminous flux was 52.4% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp  10  had been turned on for 100 hours in total. The relative luminous flux was 54.0% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp  10  had been turned on for 500 hours in total. 
   The bulb-shaped fluorescent lamp  10  having the second auxiliary amalgam  30   b  was measured for its flux-startup characteristics. As seen from  FIGS. 16 and 19 , the relative luminous flux was 53.3% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp  10  had been turned on for 0 hours in total. The relative luminous flux was 51.1% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp  10  had been turned on for 100 hours in total. The relative luminous flux was 51.8% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp  10  had been turned on for 500 hours in total. 
   The bulb-shaped fluorescent lamp  10  having the third auxiliary amalgam  30   c  was measured for its flux-startup characteristics. As seen from  FIGS. 17 and 19 , the relative luminous flux was 51.7% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp  10  had been turned on for 0 hours in total. The relative luminous flux was 53.9% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp  10  had been turned on for 100 hours in total. The relative luminous flux was 50.9% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp  10  had been turned for 500 hours in total. 
   As Comparative Example 2, a bulb-shaped fluorescent lamp was prepared, which had a conventional auxiliary amalgam comprising a stainless-steel base on which gold was plated in a usual manner. The flux-startup characteristic of this bulb-shaped fluorescent lamp was measured. As shown in  FIGS. 18 and 19 , the bulb-shaped fluorescent lamp according to Comparative Example 2 exhibited a relative luminous flux of 49.8% upon lapse of 5 seconds from the time this lamp was turned on, after the lamp  10  had been turned on for 0 hours in total. The relative luminous flux was 45.9% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp had been turned on for 100 hours in total. The relative luminous flux was 42.6% upon lapse of 5 seconds from the time the lamp  10  was turned on, after the lamp had been turned on for 500 hours in total. 
   The bulb-shaped fluorescent lamp  10  comprising the auxiliary amalgam  30   a  having the nickel layer  33  provided between the metal layer  32   a  and the base  31   a  exhibited a relative luminous flux 6.5% greater than that of the bulb-shaped fluorescent lamp of Comparative Example 2 having the conventional auxiliary amalgam, after it had been turned on for 100 hours in total. The relative luminous flux of the lamp  10  after turning on for 500 hours in total was 11.4% greater than that of Comparative Example 2. Furthermore, the relative luminous flux that the lamp  10  exhibited in the initial state (i.e., after the lamp  10  had been turned on for 0 hours in total) was 6.8% greater than that of the bulb-shaped fluorescent lamp of Comparative Example 2. 
   The bulb-shaped fluorescent lamp  10  comprising the second auxiliary amalgam  30   b  having the nickel layer  33  provided between the metal layer  32   a  and the base  31   b  exhibited a relative luminous flux 5.2% greater than that of the bulb-shaped fluorescent lamp of Comparative Example 2, after it had been turned on for 100 hours in total. The relative luminous flux that the lamp  10  exhibited after it had been turned on for 500 hours in total was 9.2% greater than that of Comparative Example 2 exhibited under the same conditions. In addition, the relative luminous flux that the lamp  10  exhibited in the initial state was 3.5% greater than that of Comparative Example 2. 
   Thus, the nickel layer  33 , which is provided between the base  31   a  and the metal layer  32   a  or  32   b,  is believed to inhibit the diffusion of gold from the metal layer  32   a  or  32   b  into the base  31   a.  Thanks to the use of the auxiliary amalgam  30   a  or  30   b,  the fluorescent lamp  12  can maintain the improved flux-startup characteristic for a long time. 
   Moreover, the bulb-shaped fluorescent lamp  10 , which has the first auxiliary amalgam  30   b  whose metal layer  32   a  has a rough surface, generated a luminous flux 3.3% (relative value) greater after it had been used for 0 hours in total, a luminous flux 1.3% (relative value ) greater after it had been used for 100 hours in total, and a luminous flux 2.2% (relative value) greater after it had been used for 500 hours in total, than that of the bulb-shaped fluorescent lamp  10  that had the second auxiliary amalgam  30   b.    
   As described above, the metal layer  32   a  is porous, with the filling ratio of the crystals set at about 80%. Some surface region of this metal layer, selected at random and differing in crystal size, had arithmetic mean roughness Ra of 0.047 μm, maximum roughness-height Ry of 0.762 μm, and ten-point average roughness Rz of 0.538 μm. This helps to inhibit the diffusion of gold from the metal layer  32   a  into the base  31   a.  Hence, the use of this auxiliary amalgam  30   a  can not only greatly enhance the flux-startup characteristic of the bulb-shaped fluorescent lamp  10 , but also maintain this improved flux-startup characteristic for a long time. 
   The bulb-shaped fluorescent lamp  10  comprising the third auxiliary amalgam  30   c  generated a luminous flux 8.0% (relative value) greater after it had been used for 100 hours in total and a luminous flux 8.3% (relative value) greater after it had been used for 500 hours in total, than the luminous flux generated by the bulb-shaped fluorescent lamp according to Comparative Example 2, which has a conventional auxiliary amalgam. Further, the luminous flux that the lamp  10  generated in the initial state was 1.9% (relative value) greater than the luminous flux that the bulb-shaped fluorescent lamp according to Comparative Example 2 generated in the initial state. 
   Gold in the metal layer  32   c  scarcely diffuses into the base  31   b.  This is probably because the base  31   b  is made mainly of molybdenum. Hence, the auxiliary amalgam  30   c  enables the fluorescent lamp  12  to maintain the improved flux-startup characteristic for a long time even though its metal layer  32   c  is thinner than that of the conventional auxiliary amalgam. 
   Another type of auxiliary amalgam that can be used in the fluorescent lamp  12 , in place of the first auxiliary amalgam  30   a,  will be described with reference to  FIG. 20 . 
   The auxiliary amalgam  30   d  shown in  FIG. 20  (hereinafter, referred to as “fourth auxiliary amalgam”) comprises a base  31   a  that is identical to the base of the first auxiliary amalgam  30   a.  The base  31   a  a stainless-steel plate that has a thickness of 40 μm and a size of 2×7 μm. A peeling-inhibiting layer  35   a  made mainly nickel and having a thickness of about 0.01 μm is formed on the base  31   a.  A diffusion-inhibiting layer  34  made mainly of molybdenum and having a thickness of about 0.05 μm is formed on the peeling-inhibiting layer  35   a.  Further, a peeling-inhibiting layer  35  made mainly of nickel and having a thickness of about 0.01 μm is formed on the diffusion-inhibiting layer  34 . On this peeling-inhibiting layer  35   b  there is formed a metal layer  32   c.  The metal layer  32   c  is made of the same material as its counterpart of the first auxiliary amalgam  30   a  and has a thickness of 0.5 μm. The metal layer  32   c  has arithmetic mean roughness Ra of 0.01 μm, maximum roughness-height Ry of 0.285 μm, and ten-point average roughness Rz of 0.01 μm. The metal layer  32   c  can be formed by, for example, ordinary bright electroplating. The peeling-inhibiting layer  35   a  is provided to lay the diffusion-inhibiting layer  34  firmly on the base  31   b,  and is not indispensable. Similarly, the peeling-inhibiting layer  35   b  is provided to lay the metal layer  32   c  firmly on the diffusion-inhibiting layer  34 , and is not indispensable. 
   In the fluorescent lamp  12  comprising the fourth auxiliary amalgam, gold in the metal layer  32   c  scarcely diffuses into the diffusion-inhibiting layer  34  that is made mainly of molybdenum. Hence, the auxiliary amalgam  30   d  enables the fluorescent lamp  12  to maintain the improved flux-startup characteristic for a long time even though its metal layer  32   c  is thinner than that of the conventional auxiliary amalgam. 
   Generally speaking, stainless steel is less expensive than molybdenum. The amalgam  30   d  that comprises the base  31   a  made of stainless steel and has the diffusion-inhibiting layer  34  made mainly of molybdenum can therefore be manufactured at a lower cost than the third amalgam  30   c  that has the base  31   b  made mainly of molybdenum. 
   The second embodiment of the present invention will be described, with reference to  FIGS. 21 and 22 . This embodiment is applied to a fluorescent lamp and a bulb-shaped fluorescent lamp comprising this fluorescent lamp. 
   This bulb-shaped fluorescent lamp  10  comprises a lamp-driving device  50 . The device  50  supplies a lamp-output power of 7 to 15 W, setting the current density (current per unit area) in the light-emitting tube  20  to 3 to 5 mA/mm 2 , thereby to drive the fluorescent lamp  12 . The fluorescent lamp  12  of the second embodiment has a rated input power of 8 W. Power of 7 W is supplied to the light-emitting tube  20  at a high frequency. The lamp current is 120 mA, and the lamp voltage is 80V. The light-emitting tube  20  emits light, providing a total luminous flux of about 480 lm. The electrodes  27  generate heat, and electric discharge takes place in the discharge path. The fluorescent lamp  12  therefore emits light. While the fluorescent lamp  12  remains on, the temperature in the vicinity of the electrodes  27  of the bent tubes  21   a  and  21   c  is 100 to 120° C., the temperature at the straight tubes  23  is 70 to 80° C., the temperature at the tops of the curved parts  24  is about 55° C., and the temperature in the globe  60  is 50 to 60° C. 
   By the turning-on of the fluorescent lamp  12 , the centers of discharge formed in the bent tubes  21   a,    21   b  and  21   c  become shifted to the shortest distance side at the tops of the curved parts  24 . Therefore, the distance between the top of each curved part  24  and the discharge path becomes long. The temperature in the globe  60  and the temperature in the tops of the curved parts  24  are about 50 to 60° C., but not so high, falling within a tolerance range, and can control the mercury-vapor pressure to provide a high lamp efficiency. Therefore, the main amalgam  26   b  can be made of an amalgam having a relatively high vapor pressure of mercury, for example, alloy composed of 49% by mass of bismuth (Bi), 36% by mass of tin (Sn) and 15% by mass of mercury (Hg). If the main amalgam  26   b  provide a high mercury-vapor pressure, the mercury-vapor pressure in the light-emitting tube  20  can remain relatively high even at normal temperature (25° C. in this instance). This can improve the flux-startup characteristic of the fluorescent lamp  12 . The auxiliary amalgam used is, for example, the first auxiliary amalgam  30   a  described above. Nonetheless, the auxiliary amalgam  30   a  may be replaced by the second auxiliary amalgam  30   b,  the third auxiliary amalgam  30   c  or the fourth auxiliary amalgam  30   d.  The second embodiment is identical to the first embodiment, in any other structural feature. Therefore, any identical structural feature will not be described. 
   As the fluorescent lamp  12  operates in the stable state, its temperature rises because the globe  60  covers the lamp  12 . A part of the light-emitting tube  20  of the fluorescent lamp  12  can be set at 70° C. or less by controlling the temperature that is determined from the surface area of the heat-generating part and the input power. This can improve the flux-startup characteristic of the fluorescent lamp  12 . 
   The bulb-shaped fluorescent lamp  10  according to the present embodiment was compared with the bulb-shaped fluorescent lamps according to Comparative Examples 3, 4, 5 and 6 in terms of flux-startup characteristic observed until the luminous flux attains 80% of its rated maximum value. The flux-startup characteristic of each lamp was determined by supplying the commercially available 100-V power to the lamp, maintaining the ambient temperature at 25° C. and positioning the lamp with the cap  42  directed upwards in no wind state. The current input and the power consumed were 140 mA and 8 W, respectively, for all bulb-shaped lamps compared. 
   The bulb-shaped fluorescent lamp according to Comparative Example 3 comprises main amalgam (Bi (49% by mass)—Sn (36% by mass)—Hg (15% by mass), which is similar to that of the bulb-shaped fluorescent lamp  10  according to this embodiment. It has auxiliary amalgam that is made mainly of indium. 
   The bulb-shaped fluorescent lamp according to Comparative Example 4 has main amalgam (Bi (49% by mass)—Sn (36% by mass)—Hg (15% by mass), which is similar to that of the bulb-shaped fluorescent lamp  10  according to this embodiment. It has no auxiliary amalgam at all. 
   The bulb-shaped fluorescent lamp according to Comparative Example 5 has main amalgam (Bi (44% by mass)—Pb (19% by mass)—Sn (34% by mass)—Hg (4% by mass), which provides a lower mercury-vapor pressure than the main amalgam used in the bulb-shaped fluorescent lamp  10  according to this embodiment. It has auxiliary amalgam that is made mainly of gold. 
   The bulb-shaped fluorescent lamp according to Comparative Example 6 has main amalgam (Bi (44% by mass)—Pb (18% by mass)—Sn (34% by mass)—Hg (4% by mass), which is similar to that of Comparative Example 5. It has auxiliary amalgam that is made mainly of indium. 
     FIG. 22  shows the results of determining the flux-startup characteristics of the lamps compared, namely illustrating how the luminous flux emitted from each lamp changed with time. The luminous fluxes emitted immediately after the lamp was turned on were: 
   This embodiment&gt;Comparative Example 4&gt;Comparative Example 5≧Comparative Example 6&gt;Comparative Example 3. 
   The luminous fluxes emitted from Comparative Examples 4 to 6 sharply decreased after the lamps were turned on, and the luminous fluxes emitted upon lapse of 1 second from the turning-on were: 
   Embodiment&gt;Comparative Example 4&gt;Comparative Example 3≧Comparative Example 6&gt;Comparative Example 5. 
   About 2 seconds from the turning-on, the lamp efficiencies (relative luminous fluxes) of Comparative Examples 3 to 6 started increasing. However, it took 10 seconds or more for Comparative Examples 3, 5 and 6 to have their luminous fluxes of 40% of their entire flux values. 
   By contrast, in the bulb-shaped fluorescent lamp  10  according to the present embodiment, the mercury-vapor pressure is high when the lamp  10  remains off. This is because the lamp  10  uses main amalgam  26   b  that can provide a high mercury-vapor pressure. Further, the luminous flux quickly increases, because the auxiliary amalgam  30   a  releases mercury in an appropriate amount immediately after the lamp  10  is turned on, and thus there is no insufficiency of mercury. It was confirmed that the lamp  10  of this embodiment attained, within 1 second after it was turned on, about 50% or more of the light output attained at the time when the lamp  10  operates in the stable state. 
   The inventors hereof conducted the following experiment to find the fact that will be described later. The light-emitting tube  20  has a surface area S, which is substantially represented by:
 
 S=πDL+ 2×(π/4) D   2   (3)
 
   where D is the diameter of a circle I surrounding the circumference of the light-emitting tube  20 , and L is the length of the light-emitting tube  20 . 
   The inventors found that the light-emitting tube  20  operating in the normal state can have a part remaining at 70° C. or less, if the surface area S of the light-emitting tube  20  has the following relation with the lamp output P:
 
P/S&lt;0.12  (4)
 
   The inventors also found that mercury or main amalgam  26   b  can be sealed to provide a mercury-vapor pressure of 0.15 Pa or more at normal temperature (25° C.) if the light-emitting tube  20  has a part that is at 70° C. or less even while the lamp is operating in the normal state. 
   A bulb-shaped fluorescent lamp having no globes  60  can operate in the same way if the following relation holds true:
 
P/S&lt;0.18  (5)
 
   The fluorescent lamp  12  according to this embodiment can maintain an improved flux-startup characteristic for a long time, as in the first embodiment. In addition, the mercury-vapor pressure can be high while the lamp  12  remains off, because the lamp  12  has the main amalgam  26   b  that provides a mercury-vapor pressure of 0.04 Pa or more at 25° C. This can enhance the flux-startup characteristic. 
   In the fluorescent lamp  12  according to this embodiment, the light-emitting tube  20  is so designed that the surface area S of the light-emitting tube  20  and the lamp output P have the relation of the formula (4). The light-emitting tube  20  can therefore have a low-temperature part that remains at 70° C. or less even while the lamp  12  is operating in the normal state. Thus, the light-emitting tube  20  can contain mercury or the main amalgam  26   b  that provides a mercury-vapor pressure-of 0.15 Pa or more at 25° C. This enables the fluorescent lamp  12  according to this embodiment to have its flux-startup characteristic improved even more, as compared to the fluorescent lamp of the first embodiment. 
   The third embodiment of the present invention will be described, with reference to  FIGS. 23 and 24 . This embodiment is a fluorescent lamp and a bulb-shaped fluorescent lamp comprising the fluorescent lamp. 
     FIG. 23  depicts the electrode-less bulb-shaped fluorescent lamp  110  as a bulb-shaped fluorescent lamp. The electrode-less bulb-shaped fluorescent lamp  110  comprises an electrode-less fluorescent lamp  130  as a fluorescent lamp, a cover  111 , and a lamp-driving device  112 . The cover  111  comprises a cover body  111   b,  a cap  111   a,  and a holder  114 . The cap  42  is provided at one end of the cover body  111   b.  The holder  114  is provided at the other end of the cover body  111   b  and used as a holding part. The lamp-driving device  112  is contained in the cover  111 . The electrode-less fluorescent lamp  130  is shaped like a bulb. The holder  114  holds the fluorescent lamp  130 . 
   The fluorescent lamp  130  and the cover  111  constitute an envelope  120 . The envelope  120  is formed, having a size similar to the standard size of bulbs for general lighting use, such as incandescent lamps which have the rated power of 60 W. The fluorescent lamp  130  has height H 3  of about 110 to 140 mm, including that of the cap  111   a,  and outside diameter D 4  of about 50 to 70 mm. The cover  111  has outside diameter D 5  of about 50 mm. The phrase “bulbs for general lighting use” means the bulbs defined at JIS C 7501. 
   The fluorescent lamp  130  comprises a light-emitting tube  113 , a mercury pellet  26   c  (Zn (50% by mass)—Hg (50% by mass), and auxiliary amalgam  30   a.  The light-emitting tube  113  is made of material transparent to light such as glass and shaped like a ball. More precisely, the light-emitting tube  113  has a ball-shaped part  113   c,  a ring-shaped edge part  113   b,  and a hollow part  113   a.  The ball-shaped part  113   c  has an opening at one end. The edge part  113   b  extends inwards from the rim of the opening. The hollow part  113   a  is hollow cylinder having a bottom and extending from the tip end of the edge part  113   b  substantially toward the center of the ball-shaped part  113   c.  The ball-shaped part  113   c,  edge part  113   b  and hollow part  113   a  are integrally formed. 
   An exhaust pipe  115  is provided in the hollow part  113 . The pipe  115  extends from the center of the bottom toward the opening (toward the edge part  113   b ) along the axis of the hollow part  113   a.  The mercury pellet  26   c  is sealed in the light-emitting tube  113  and positioned near the edge part  113   b.  The mercury pellet  26   c  is secured to, for example, the inner surface of the edge part  113   b.  The In the fluorescent lamp  130 , the mercury pellet  26   c  may be replaced by the main amalgam  26   b  for use in the fluorescent lamp  12  according to the second embodiment. 
   A wire  117   a  as a supporting member extends from the hollow part  113   a  that lies in the discharge space within the light-emitting tube  113 . Auxiliary amalgam  30   a  is attached the wire  117   a.  The main amalgam  30   a  releases the mercury adsorbed to it during the initial phase of light-emission, in order to enhance the flux-startup characteristic. The auxiliary amalgam  30   a  provided in the fluorescent lamp  130  is identical to the first auxiliary amalgam  30   a  described above. The auxiliary amalgam  30   a  may be replaced by any one of the second to fourth auxiliary amalgams  30   b,    30   c  and  30   d.  The auxiliary amalgam  30   a  is supported by the wire  117   a  attached to the hollow part  113   a,  but its position is not particularly limited. Further, the shape of the auxiliary amalgam  30   a  is not limited to a particular one. 
   An alumina (Al 2 O 3 ) protection film (not shown) is formed on the inner surface of the light-emitting tube  113 , or on the inner surface of the ball-shaped part  113   c  and outer surface of the hollow part  113   a.  A phosphor layer (not shown) made of three-wave emitting phosphor is formed on the alumina protective film. 
   The light-emitting tube  113  is filled with argon gas at a filling pressure of 100 to 300 Pa, constituting at least 99% of all gas in the tube  20 . 
   The lamp-driving device  112  has a disc-shaped circuit board  112   a  and a plurality of electronic components  112   b.  The electronic components  112   b  are mounted on the circuit board  112   a.    
   The lamp-driving device  112  is secured to one side of the holder  114 . The fluorescent lamp  130  is attached the other side of the holder  114 . The holder  114  has a holding part  114   a  and a hollow cylindrical part  114   b.  The holding part  114   a  is flat and circular and can hold, on one side, the circuit board  112   a  of the lamp-driving device  112 . The hollow cylindrical part  114   b  projects from the center of the other side of the holder part  114   a.  The holding part  114   a  and the hollow cylindrical part  114   b  are integrally formed. The hollow cylindrical part  114   b  is arranged in the region defined by the outer surface of the hollow part  113   a.  The exhaust pipe  115  is arranged in the hollow cylindrical part  114   b.    
   The hollow cylindrical part  114   b  functions as a core around which an excitation coil is wound. An excitation coil  118 , which generates a high-frequency magnetic field, is wound around the outer peripheral portion of the hollow cylindrical part  114   b.  A cylindrical core bar (not shown) made of ferrite is provided in the excitation coil  118 . 
   The fluorescent lamp  130  and the holder  114  are attached to the cover body  111   b,  covering the opening made in one end (lower end) of the cover body  111   b.  Thus, the lamp-driving device  112  mounted on the holder  114  is placed in the space provided between the cover body  111   b  and the holder  114 . The cap  111   a,  such as an E26-type cap, is mounted on the other end of the cover body  111   b.  The cap  111   a  is secured to the cover body  111   b  with adhesive or by means of caulking. 
   How the electrode-less, bulb-shaped fluorescent lamp  110  is assembled will be described below. 
   First, the holder  114  is prepared in which the lamp-driving device  112  is attached to the holding part  114   a,  and the coil  18  is wound around the hollow cylindrical part  114   b.  The fluorescent lamp  130  is attached to the holding part  114   a  that now holds the lamp-driving device  112 . At this time, the light-emitting tube  113  and holder  114  are secured to the inner surface of one side (lower side) of the cover  111  by means of an adhesive such as a silicone resin. The cap  111   a  is attached to the cover  111 . The electrode-less, bulb-shaped fluorescent lamp  110  is thereby assembled. The light-emitting tube  113 , excitation coil  118  and lamp-driving device  112  may be coupled by any other method. 
   In the electrode-less, bulb-shaped fluorescent lamp  110 , the excitation coil  118  and light-emitting tube  113  generates heat as a current flows through the coil  118 . As a result, discharge takes place in the discharge path. The fluorescent lamp  130  emits light. That is, the lamp-driving device  112  receives the lamp power of 10 to 20 W and applies a tube-wall load of 500 to 1,000 W/m 2  to the light-emitting tube  113 , causing the fluorescent lamp  130  to emit light. The electrodeless, bulb-shaped fluorescent lamp  110  according to this embodiment has a rated input power of 12 W. Power of 11 W is supplied at high frequency to the fluorescent lamp  130 . When the fluorescent lamp  130  emits light, the electrode-less, bulb-shaped fluorescent lamp  110  provides a total luminous flux of about 800 lm. 
   In the electrode-less, bulb-shaped fluorescent lamp  110  according to this embodiment, the discharge space defines a surface area of 14,000 mm 2  and the tube-wall load is 790 W/m 2 . A part of the light-emitting tube  113  remains at a relatively low temperature of 50° C. or less even while the tube  113  is emitting light. The main amalgam can therefore be one that provides a comparatively high mercury-vapor pressure. The mercury-vapor pressure in the light-emitting tube  113  can remain comparatively high at normal temperature (about 25° C.). 
   The electrode-less, bulb-shaped fluorescent lamp  110  according to the present embodiment and an electrode-less, bulb-shaped fluorescent lamp according to Comparative Example 7 were turned on and compared in terms of flux-startup characteristic observed until the luminous flux attains 80% of the rated maximum value. The flux-startup characteristic of each lamp was determined by supplying the commercially available 100-V power to the lamp, maintaining the ambient temperature at 25° C. and positioning the lamp with the cap  42  directed upwards in no wind state. The power consumed was about 12 W. 
   The electrode-less, bulb-shaped fluorescent lamp according to Comparative Example 7 comprises a mercury pellet of the same type as used in the electrode-less, bulb-shaped fluorescent lamp  110  according to this embodiment, but has no auxiliary amalgams. 
     FIG. 24  shows the characteristics determined. Namely, it illustrates how the luminous fluxes emitted from the fluorescent lamps changed with time. In terms of relative light output (relative luminous flux) immediately after turning-on, the lamps had the following relation: 
   This embodiment&gt;Comparative Example 7 
   Immediately after the lamp according to Comparative Example 7 was turned on, its luminous flux sharply decreased. Even 1 second from the turning-on. In terms of relative light output, the lamps had the following relation in terms of relative light output: 
   This embodiment&gt;Comparative Example 7 
   Using a mercy pellet that provides a relatively high mercy-vapor pressure, the lamp according to Comparative Example 7 output about 65% of the output value at the stable state, from the time when it is turned on. However, its output could not reach 70% or more of the output value at the stable state, after 20 seconds had passed from the turning-on. 
   By contrast, the mercury-vapor pressure is high in the electrode-less bulb-shaped fluorescent lamp  110  according to this embodiment, while the lamp  110  remains off. This is because the lamp  110  uses the main amalgam  26   b  that provides a high mercury-vapor pressure. Moreover, the auxiliary amalgam  30   a  releases mercury in an appropriate amount, causing no insufficiency of mercury. Thus, the luminous flux increases fast. It was confirmed that the light output of the present embodiment reached, within one second after turning on, about 50% or more of the value it should have while the lamp is operated in the stable state. 
   Having the auxiliary amalgam  30   a,  the electrode-less bulb-shaped fluorescent lamp  110  according to this embodiment can have an improved flux-startup characteristic for a long time, as in the first embodiment. Further, the mercury-vapor pressure can be high while the lamp  12  remains off, because the lamp  12  has the mercury pellet  26   c  that provides a mercury-vapor pressure of 0.04 Pa or more at 25° C. This can enhance the flux-startup characteristic. 
   The fourth embodiment of the present invention will be described, with reference to  FIG. 25 . This embodiment is a compact fluorescent lamp. The compact fluorescent lamp  70  comprises a light-emitting tube  71 , main amalgam  26   a,  auxiliary amalgam  30   a  and a cap  80 . 
   The light-emitting tube  71  has straight bulbs that are made of glass transparent to light and have an inside diameter of 1 mm to 15 mm. More specifically, the light-emitting tube  71  has a pair of straight bulbs  72  that have an inside diameter of 13 mm and an outside diameter of 15 mm. The straight bulbs  72  are arranged side by side and communicate with each other at their distal-end parts, via a bridge-shaped connecting part  73 . Thus, the light-emitting tube  71  is H-shaped. The straight bulbs  72  are fastened together, at middle part, with thermosetting adhesive  74 , such as silicone resin. A phosphor film (not shown) is formed on the inner surface of the each bulb  72 . The main amalgam is, for example, the main amalgam  26   b  described above. The auxiliary amalgam is, for example, the first auxiliary amalgam  30   a  described above. The main amalgam  26   b  may be replaced by the main amalgam  26   a.  The auxiliary amalgam  30   a  may be replaced by any one of the second to fourth auxiliary amalgams  30   b,    30   c  and  30   d.    
   The light-emitting tube  71  is filled with rare gas, such as argon, and mercury. The mercury filled in the tube  71  has resulted from the main amalgam  26   b  and auxiliary amalgam  30   a  that are sealed in the light-emitting tube  71 . 
   The ends of the light emitting tube  71 , or the capped ends of the straight bulbs  72 , contain two filament electrodes  33 , respectively. Each filament electrode  93  is supported through wells  85  by a stem  84 .  FIG. 25  shows only the filament electrode provided in one straight bulb  72 . In the capped end of each straight bulb  72 , a thin tube  78  is provided and extends toward the electrode. The main amalgam  26   b  is provided in, for example, the thin tubes  78 . The auxiliary amalgam  30   a  is attached to, for example, wells  85  that hold the filament electrodes  83 . 
   The cap  80  has a cap body  80   a  and four cap pins  80   b.  The cap pins  80   b  project from one end of the cap body  80   a.  The cap  80  is, for example, a GY10q type designed for compact fluorescent lamps. 
   The cap body  80   a  is made of, for example, electrically insulating synthetic resin. It is shaped like an oblate disc, having two ends that are almost flat. It has, in one end, a pair of insertion holes  81  into which the capped ends of the straight bulbs  72  of the light-emitting tube  71  are inserted. Further, the cap body  80   a  has, in one end, too, two recesses  82  that are continuous to the insertion holes  81 , respectively. The thin tubes  78  are located in these recesses  82 . The recesses  82  are positioned side by side. The cap  80  and the light-emitting tube  71  are secured to each other with adhesive such as silicone resin. 
   In the compact fluorescent lamp  70 , which has thin bulbs  72  and can yet generate a sufficient light output, the center of discharge caused in the light-emitting tube  72  when the lamp  70  is turned on is located very close to the connecting part  73 . The distal ends of the straight bulbs  72  therefore lie at a long distance from the center of discharge. Hence, the temperature in the light-emitting tube  71  may be high while the compact fluorescent lamp  70  remains on. Nonetheless, the temperature in the distal ends of the straight bulbs  71  can be so low that the mercury-vapor pressure can be controlled to attain sufficient lamp efficiency. This is why the lamp  70  can use the main amalgam  26   b  that provides a relatively high mercury-vapor pressure. 
   In the compact fluorescent lamp  70 , mercury is likely to accumulate in the distal ends of the straight bulbs  72 . The mercury is hardly heated immediately after the lamp  70  is turned on. It is therefore desirable not to lower the mercury-vapor pressure too much in the light-emitting tube  71  as long as the lamp  70  remains off. In view of this, it is desirable to provide an auxiliary amalgam such as the auxiliary amalgam  30   a  made mainly of gold, silver, palladium, platinum, lead, tin, zinc or bismuth. If the auxiliary amalgam is so made, the lamp  70  can have an improved flux-startup characteristic for a long time. 
   As described above, the compact fluorescent lamp  70  according to the present embodiment uses the main amalgam  26   b  that provides a high mercury-vapor pressure and the auxiliary amalgam  30   a  that does not absorb mercury in the light-emitting tube  71  to an access while the lamp  70  remains off. The mercury-vapor pressure in the fluorescent lamp  70  can remain relatively high at normal temperature. This improves the flux-startup characteristic. Moreover, the flux-startup characteristic thus improved can be maintained for a long time. 
   The bulb-shaped fluorescent lamps  10  according to the first and second embodiments can be used in, for example, the lighting apparatus  1  shown in  FIG. 26 . The lighting apparatus  1  is a down light fitted in a ceiling C. It comprises a main body  2 , a socket  3  and a bulb-shaped fluorescent lamp  10 . The socket  3  is secured to the main body  2 . The lamp  10  is attached to the socket  3 . 
   The bulb-shaped fluorescent lamp  10  configured as described above can be used in the lighting apparatus  1 , in place of a bulb for general lighting use. In this case, the light emitted by the lamp  10  can be applied in a sufficient amount to the reflector provided in the main body  2  and located near the socket  3 , if it is distributed in the same way as the light emitted by the bulb for general lighting use. This enables the lighting apparatus  1  to acquire such an operating characteristic as designed. Furthermore, if the lighting apparatus  1  is a table lamp that has a cloth shade through which light diffuses, the bulb-shaped fluorescent lamp  10  can distribute light almost in the same way as the bulb for general lighting use. 
   The main body  2  can be a new one or one already fitted in the ceiling, and can set the bulb-shaped fluorescent lamp  10  if it has a socket  3  to which the cap  42  can be detachably connected. The lighting apparatus  1  is not limited to a down light. It can have any other type of a main body  2  that can directly hold the bulb-shaped fluorescent lamp  10 . 
   The lighting apparatus  1  may have the electrodeless, bulb-shaped fluorescent lamp  110  according to the third embodiment, in place of the bulb-shaped fluorescent lamp  10 . The compact fluorescent lamp  70  according to the fourth embodiment needs to be used in lighting apparatuses different from the light apparatus  1 . It finds use in, for example, a lighting apparatus that comprises a main body, a socket that can hold the cap  80 , e.g., GY10q type designed for compact fluorescent lamps, and a lamp-driving device for driving the compact fluorescent lamp  70 . 
   The metal layers  32   a  to  32   c  of the auxiliary amalgams  30   a  to  30   d,  respectively, are made mainly of gold. They are not limited to gold layers, nevertheless. Metal layers, each containing at least one element selected from the group consisting of gold, silver, palladium, platinum, lead, tin, zinc and bismuth, have common property of not absorbing mercury to an excess while the lamp remains off. 
   The present invention can provide a fluorescent lamp that exhibits good flux-startup characteristic for a long time. Further, the invention can provide a bulb-shaped fluorescent lamp that is similar to an incandescent lamp and exhibits good flux-startup characteristic for a long time. Still further, the invention can provide a lighting apparatus that has the fluorescent lamp or the bulb-shaped fluorescent lamp.