# US 7,411,350 B2 · Small arc tube, low-pressure mercury lamp, lighting apparatus, mandrel for forming the arc tube, and production method of the arc tube > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,411,350 B2 - Document ID: US7411350B2 - Status: Granted - Kind: B2 - Application number: 10/918,302 - Filed: 2004-08-13 - Published: 2005-04-14 - Granted: 2008-08-12 - Earliest claimed: 2003-09-02 - Assignees: Matsushita Electric Industrial Co., Ltd. - Inventors: Shiro Iida; Noriyuki Uchida; Tatsuhiro Yabuki - Web page: https://patentgrep.com/patent/US7411350B2 ## CPC - H01J 61/72: having a main light-emitting filling of easily vaporisable metal vapour, e.g. mercury - H01J 9/247: {specially adapted for gas-discharge lamps} - H01J 61/327: {"Compact"-lamps, i.e. lamps having a folded discharge path} - H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H) ## Abstract A mandrel has a main body having a substantially-cone-shape. The main body has, on its circumferential surface, a spiral-shaped groove at which the glass tube to be wound is held. The groove, in cross section, has a contact range in which the glass tube's circumferential surface is in contact. One end of the contact range corresponds to a circumference part of the glass tube in wound state which is closest to the axis of the main body of the mandrel, a part of the groove that extends from the circumference part towards the apex of the main body is parallel to the axis of the mandrel, and the pitch of the groove in the axial direction of the mandrel is formed smaller than the outer diameter of the glass tube. The glass tube wound on the mandrel is easily removed from the main body by lowering the mandrel. In the arc tube formed in such a way, any two glass tube portions, which are adjacent to each other in the axial direction of the arc tube, overlap with each other. ## Claims ### Claim 1 An arc tube comprising: an arc-tube body made of a single glass tube that is wound around an axis from a middle part to both ends, to form a spiral broadening out from the middle part to each of the ends in the axial direction; and electrodes respectively sealed to the ends of the arc-tube body, wherein a gap exists between any two glass tube portions adjacent to each other in a direction orthogonal to the axis when the arc-tube body is viewed in the axial direction, and any two glass tube portions adjacent in the axial direction overlap with each other when the arc-tube body is viewed in the direction orthogonal to the axis, wherein the overlapping of any two glass tube portions, when the arc-tube body is viewed in the direction orthogonal to the axis, is smaller than 0.5 times an outer diameter of the glass tube. ### Claim 2 (depends on 1) The arc tube of claim 1, wherein an inner diameter of the glass tube is in a range of 6.5 mm to 9.5 mm, inclusive. ### Claim 3 (depends on 2) The arc tube of claim 2, wherein a bulb wall loading is set in a range of 0.10 W/cm2 l to 0.22 W/cm2, inclusive. ### Claim 4 (depends on 1) The arc tube of claim 1 further including mercury. ### Claim 5 (depends on 4) The arc tube of claim 4 further including a buffer gas. ### Claim 6 (depends on 4) The arc tube of claim 4 further including a ballast member operatively committed to the arc tube to activate the arc tube as a low-pressure mercury lamp. ### Claim 7 (depends on 1) The arc tube of claim 1 wherein the overlap of the glass tube portion of the spiral adjacent each other when viewed from a side direction orthogonal to the axis is within a range of greater than 0% to 50% or below of the outer diameter of the glass tube. ### Claim 8 A low pressure arc tube comprising: an arc-tube body made of a single elongated glass tube with respective ends that is wound around an axis from a middle part towards each of the respective ends to form a spiral broadening out from the middle part to each of the ends in the axial direction; and an electrode respectively sealed to each end of the arc-tube body, wherein a gap is positioned between any two adjacent glass tube portions in a radial direction orthogonal to the axis when the arc-tube body is viewed downward along the axial direction, and all glass tube portions adjacent to each other radially project outwardly, in a direction orthogonal to the axis, a continual source of light with no gaps as a result of adjacent glass tube portions overlapping with each other when viewed radially in a direction orthogonal to the axis wherein the overlapping tube portions and the arc tube body when viewed in the direction orthogonal to the axis, is smaller than 0.5 times an outer diameter of the glass tube. ### Claim 9 (depends on 8) The arc tube of claim 8, wherein an inner diameter of the glass tube is in a range of 6.5 mm to 9.5 mm, inclusive. ### Claim 10 (depends on 9) The arc tube of claim 9, wherein a bulb wall loading is set in a range of 0.10 W/cm2 to 0.22 W/cm2, inclusive. ### Claim 11 (depends on 10) The arc tube of claim 10 wherein the single glass tube is made substantially of strontium-barium silicate. ### Claim 12 (depends on 11) The arc tube of claim 11 wherein the single glass tube has an inner phosphor surface comprising a red, a blue and a green rare earth phosphor.