201237925 六、發明說明： 【發明所屬之技術領域】 本發明係有關於放電容器外表面具有一對光透過性外 部電極之準分子燈，特別是於放電容器內面配置有啓動輔 助電極之準分子燈。 【先前技術】 習知技術中，有於放電容器外表面相對向配置一對外 部電極而成之準分子燈，於該放電容器之光放射面處所形 成之外部電極，因其必須滿足燈具讓光透過之基本功能， 故採用例如將金膠塗佈成格子狀之光透過性電極。 另一方面，與前述光放射面相對，不讓光透過之另一 側外表面處形成之外部電極，雖在功能上無需具備光透過 性，但多數情況下，考量製程的簡化，及該放電容器內發 生放電之安定性等等，仍與前述光放射面同樣採用光透過 性電極。 爲改善此類準分子燈之啓動性，習知有在放電容器內 面設置導電性物質所成之啓動輔助電極，以達到該目的。 舉例來說，日本特開平1 1 -2 7 3 629號公報（專利文獻1 )即 爲如此。設於發光管外表面處的一對外部電極之其中一端 部，於該發光管內表面處設有導電性材料所成之啓動輔助 電極。依該文獻揭示，該啓動輔助電極係設於外部電極之 間，但未必一定須與兩外部電極重疊。 圖8所示即爲使用光透過性電極做爲外部電極之準分 201237925 子燈，放電容器11之外表面處，相對向配置一對光透過性 之外部電極12。該外部電極12之其中一端部，於放電容器 11之內表面處設有啓動輔助電極13。 像這樣配置啓動輔助電極13，例如從一方之外部電極 12施加高頻率高電壓來點燈時，電荷會經由該啓動輔助電 極迅速移動至另一方之外部電極，啓動性便獲得提升。 然而，前述啓動輔助電極1 3與外部電極1 2之間所產生 的放電，不只在啓動時，於正常點燈後仍會產生放電，該 現象如圖所示，會以沿面放電X的形式朝外部電極12的方 向傳遞。 當發生沿面放電X時，相對地會消耗同等的能量，原 本外部電極之間的正規放電所需之全體能量會減少，導致 照度降低。 又，該沿面放電X發生之部位亦會發生部分照度降低 的問題，並非吾人所願。 有關此類防止啓動輔助電極與外部電極之間產生沿面 放電之技術，如日本特開20 1 0-22 5 3 43號公報（專利文獻2 )當中所揭示，設有從光透過性電極之端部朝軸方向延伸 之枝狀電極。 圖9所示即爲該習知例，設有從放電容器1 1外表面之 光透過性外部電極1 2的端部，朝軸方向延伸之枝狀電極1 4 。前述放電容器11之內面，設有導電性物質所成之啓動輔 助電極13，該啓動輔助電極13介於前述枝狀電極14之先端 部與放電容器11之間，彼此重疊。 -6- 201237925 此習知技術之構造中，啓動輔助電極1 3係對應於該枝 狀電極1 4之端部而形成，故可增加該外部電極1 2與啓動輔 助電極1 3之間的距離，使得沿面放電不容易產生。 不過.，近來使用者講求準分子燈提高照度，連帶要求 燈具必需具備更高的輸入電壓，故即使以前述之習知構成 ，啓動輔助電極1 3產生之沿面放電X仍會沿著枝狀電極1 4 到達外部電極1 2，而對外部電極1 2之間的正規放電造成影 響。若依前述習知技術之構成，要避免這個問題，可令枝 狀電極14朝管軸方向延伸更長的距離，但這樣一來會使得 燈具全長變長，綜合考量有效發光長度，其不具實用價値 ，無法令人接受。 〔先前技術文獻〕 〔專利文獻〕 [專利文獻1]日本特開平1 1 -273 629號公報 [專利文獻2]日本特開20 1 0-225 3 43號公報 【發明內容】 〔發明所欲解決之課題〕 本發明有鑑於前述習知技術之問題點，乃提供一種準 分子燈，係於放電容器的外表面至少一方設有具光透過性 之一對外部電極，前述放電容器內面配置有啓動輔助電極 而成之準分子燈，其特徵爲在有限的空間內設置沿面距離 盡可能最長的枝狀電極，使前述啓動輔助電極產生的沿面 放電沿著該枝狀電極傳遞，而不會到達外部電極，不影響 201237925 外部電極之間的正規放電。 〔用以解決課題之手段〕 爲解決上述課題，本發明當中，前述 狀電極，該枝狀電極係由根部與枝部構成 部電極的軸方向之端部沿前述放電容器之 該枝部從該根部之先端朝前述放電容器的 前述啓動輔助電極，至少與一方之前述外 極的枝部先端彼此重疊配置。 又，其特徵爲前述枝狀電極之根部， 極之寬度方向的一端部沿管軸方向延伸， 根部之先端朝前述放電容器之寬度方向的 又，其特徵爲前述枝狀電極的前述根 連接部寬度，較前述枝部的寬度來得大。 又，其特徵爲前述枝狀電極的枝部之 該枝部其他部分的寬度來得大。 〔發明之功效〕 根據本發明，設於外部電極處之枝狀 軸方向延伸之根部及沿寬度延伸之枝部所 助電極與枝狀電極的枝部先端之間最初所 ’會沿此枝部傳遞出去。相對於此，從前 到外部電極的直線路徑上之空隙部並不存 面電荷不會累積，不會形成電位，故於空 外部電極設有枝 ，該根部從該外 管軸方向延伸， 寬度方向延伸； 部電極的枝狀電 係從前述外部電 前述枝部係從該 另一端部延伸。 部與前述枝部的 先端部寬度，較 電極，係由沿管 構成，故啓動輔 發生的沿面放電 述啓動輔助電極 在電極，玻璃內 隙部方向不會產 -8- 201237925 生電場，不會朝外部電極方向發生沿面放電。 此外，前述枝狀電極的根部，係從外部電極的端部的 寬度方向之一端部延伸出去，使枝部的長度增長至最大限 度，增加枝狀電極的全長，可確實防止沿面放電到達外部 電極。 此外，與枝狀電極的枝部相比，根部與枝部的連接部 分寬度較寬，使電極部中具有較廣面積之連接部分蓄積較 多電荷。藉此，啓動輔助電極與枝部先端之間最初發生的 沿面放電，會朝向此電荷蓄積較多的連接部方向，更易沿 前述枝部傳遞。 再者，增加枝狀電極的枝部之先端部寬度，如此一來 於啓動輔助電極與該寬度較寬的先端部之間，玻璃內面較 易累積電荷，該兩者間更易發生最初之沿面放電。此最初 之沿面放電，會如前述般沿枝部傳遞出去，故啓動輔助電 極與外部電極之間的直線路徑上，不會發生沿面放電。 藉此，無需增長燈具的全長，也能增加沿面放電傳遞 的距離，使其不會到達外部電極，不會對原本外部電極之 間的正規放電帶來不良影響，是爲其功效。 【實施方式】 如圖1所示，本發明之準分子燈1的放電容器2上，其 兩面相對向配置有一對光透過性之外部電極3、3。 如圖2以後之各圖所詳示，前述各外部電極3之端部上 設有略L字狀之枝狀電極4。該枝狀電極4由根部5及枝部6 -9 - 201237925 所構成，該根部5係沿前述外部電極3於放電容器2的寬度 方向之一端朝管軸方向延伸，前述枝部6從該根部5之先端 朝放電容器2之寬度方向的另一端側延伸。 特別是如圖2中A-A處剖面的圖3，或如只取出枝狀電 極與啓動輔助電極的立體圖圖5如示，前述放電容器2內面 設有導電性物質所成之啓動輔助電極7。此啓動輔助電極7 介於前述枝狀電極4之枝部6的先端部6a、以及放電容器2 之間，呈重疊配置。 上述構成中，於準分子燈啓動時，施加於一方之外部 電極3之高頻率電流，會形成一種電容耦合狀態，穿過構 成放電容器2之介電體壁，於是高頻率電流會流向另一方 之外部電極3，使其容易發生放電，提升啓動性。 此時，連接於外部電極3之枝狀電極4呈略L字狀’累 積在啓動輔助電極7的電荷會沿著形成枝狀電極4的部位’ 亦即沿枝部6移動’其後沿根部5移動’藉由這樣沿著長路 徑移動，便不會到達外部電極3 °而啓動輔助電極7與外部 電極3之間的最短路徑上’枝狀電極並不存在’其間並不 會發生電荷的移動，故啓動輔助電極7與外部電極3之間便 難以發生沿面放電。 進一步詳述之，燈具啓動時’與枝狀電極4的枝部6相 對向之玻璃管（放電容器2)內面會累積電荷’形成電位 〇 啓動輔助電極7與前述枝部6的先端部6a之間介著玻璃 彼此重疊，其間的距離非常之小’故會產生強電場’並沿 -10- 201237925 此部位發生沿面放電。 此處的放電結束後，接著沿枝部6往根部5方向移動的 順序，持續於啓動輔助電極7與枝部6之間發生放電。亦即 ，發生的沿面放電會沿枝狀電極4的枝部6而移動。 另一方面，枝狀電極4的枝部6之先端部6 a與外部電極 3之間，並無使兩者連結形成短路的枝狀電極，故玻璃內 面不會累積電荷，不會形成電位。因此，連結啓動輔助電 極7與外部電極3的直線方向上，玻璃表面不會產生電場， 不會朝該外部電極3方向發生沿面放電。 圖6所示者爲其他實施例，枝狀電極4的根部5與枝部6 的連接部8之寬度，較前述枝部6的寬度來得大。 藉此構成，面積較廣之連接部8會蓄積較多電荷，使 得啓動輔助電極7與枝部6的連接部8方向之電場變強，故 該啓動輔助電極7與枝部6的先端部6a之間所發生的沿面放 電，更容易朝此連接部8方向移動。因此，將更可防止從 枝狀電極4的枝部6直接朝向外部電極3發生沿面放電^ 此外，圖7所示爲另一實施例，枝狀電極4的枝部6之 先端部6 a的寬度，較其他區域部分的寬度來得大》 藉此構成，該先端部6a會蓄積較多電荷，使得此部分 與啓動輔助電極7之間較易發生沿面放電，防止該啓動輔 助電極7朝向外部電極3發生放電。 又，上述實施例中，枝狀電極4的根部5，是從外部電 極3的寬度方向之一端部朝管軸方向延伸，但未必非得精 確地從一端部延伸，只要是在寬度方向的端部上，皆可適 -11 - 201237925 當選擇位置。 在此情形下，枝狀電極4的L字形狀中於寬度方向延伸 形成的枝部6長度，相較於圖9所示習知技術之枝狀電極14 ，既使不改變放電容器2的全長，仍可增加沿面放電傳遞 的距離。 不過，如上述實施例所示，令枝狀電極4的根部5從外 部電極3的寬度方向之一端部延伸，使枝部6的長度增長至 最大限度，較爲理想。 此外，所示之啓動輔助電極7，是與一對外部電極3、 3的枝狀電極6、6兩者彼此重疊，但未必非得與兩者重疊 ，亦可以僅與一方的枝狀電極6重疊配置即可，這點和前 述習知技術1相同。 再者，所示之一對外部電極3皆爲光透過性電極，但 亦可僅令放電容器的光放射面側之外部電極具光透過性， 而另一側的外部電極不具光透過性，也就是所謂的板狀電 極。 如以上說明，本發明之準分子燈，係於放電容器外表 面之光透過性外部電極的端部，設置由根部及枝部所成之 枝狀電極，且於放電容器內面，將啓動輔助電極配置於至 少一方之前述外部電極的枝狀電極的枝部先端，並與其重 疊，使啓動輔助電極與枝部先端之間發生的沿面放電沿該 枝部移動，如此一來放電不會朝外部電極方向直線進行， 不會對外部電極之間的正規放電產生不良影響。 -12- 201237925 【圖式簡單說明】 [圖1]本發明準分子燈之立體圖。 [圖2]圖1之俯視圖。 [圖3]圖2之A-A剖面圖。 [圖4]圖2之B-B部分剖面圖。 [圖5]圖1中枝狀電極與啓動輔助電極之間的關係示意 圖。 [圖6]其他實施例之部分俯視圖。 [圖7]另一實施例之部分俯視圖。 [圖8 ]習知技術之俯視圖（A )及其剖面圖（B )。 [圖9]其他習知技術之俯視圖。 【主要元件符號說明】 1 :分子燈 2 :放電容器 3 :外部電極 4 :枝狀電極 5 :根部 6 :枝部 6a :先端部 7 :啓動輔助電極 8 :連接部 1 1 :放電容器 1 2 :外部電極 -13- 201237925 1 3 :啓動輔助電極 14 :枝狀電極 X :沿面放電 -14-201237925 VI. Description of the Invention: [Technical Field] The present invention relates to an excimer lamp having a pair of light transmissive external electrodes on the outer surface of the discharge vessel, in particular, an excimer having an auxiliary auxiliary electrode disposed on the inner surface of the discharge vessel light. [Prior Art] In the prior art, there is an excimer lamp in which a pair of external electrodes are disposed opposite to the outer surface of the discharge vessel, and an external electrode formed at a light emitting surface of the discharge vessel is required to satisfy the light of the lamp. Since the basic function is transmitted, for example, a light-transmitting electrode in which gold paste is applied in a lattice shape is used. On the other hand, the external electrode formed on the outer surface of the other side that does not allow light to pass through, as opposed to the light-emitting surface, does not need to have optical transparency in function, but in many cases, the simplification of the process and the discharge are considered. The stability of the discharge occurring in the container, etc., is also the same as that of the light-emitting surface. In order to improve the startability of such an excimer lamp, it is known to provide an auxiliary auxiliary electrode formed by providing a conductive material inside the discharge vessel to achieve the object. This is the case, for example, in Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. Hei. One end of a pair of external electrodes disposed on the outer surface of the arc tube is provided with an auxiliary auxiliary electrode formed of a conductive material at the inner surface of the arc tube. According to this document, the starting auxiliary electrode is provided between the external electrodes, but does not necessarily have to overlap the two external electrodes. Fig. 8 shows a sub-divided 201237925 sub-light using a light-transmitting electrode as an external electrode, and a pair of light-transmitting external electrodes 12 are disposed opposite to each other on the outer surface of the discharge vessel 11. One end portion of the external electrode 12 is provided with a starting auxiliary electrode 13 at the inner surface of the discharge vessel 11. When the activation auxiliary electrode 13 is disposed in this manner, for example, when a high frequency and a high voltage are applied from one of the external electrodes 12 to turn on the light, the electric charge is rapidly moved to the other external electrode via the activation auxiliary electrode, and the startability is improved. However, the discharge generated between the aforementioned auxiliary electrode 13 and the external electrode 12 is not only generated at the time of starting, but also after the normal lighting, which is shown as a creeping discharge X as shown in the figure. The direction of the external electrode 12 is transmitted. When the creeping discharge X occurs, the same energy is consumed relatively, and the total energy required for the regular discharge between the external electrodes is reduced, resulting in a decrease in illuminance. Further, the portion where the creeping discharge X occurs also causes a problem that the partial illuminance is lowered, which is not what we wish. A technique for preventing creeping discharge between the auxiliary electrode and the external electrode is disclosed. For example, as disclosed in Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. 20 1 0-22 5 3 43 (Patent Document 2), the end of the light transmissive electrode is provided. a branch electrode extending in the axial direction. This conventional example is shown in Fig. 9, and a branch electrode 14 extending in the axial direction from the end of the light transmissive external electrode 12 on the outer surface of the discharge vessel 1 is provided. The inner surface of the discharge vessel 11 is provided with a starting auxiliary electrode 13 made of a conductive material, and the starting auxiliary electrode 13 is interposed between the tip end portion of the branch electrode 14 and the discharge vessel 11, and overlaps each other. -6- 201237925 In the configuration of the prior art, the auxiliary auxiliary electrode 13 is formed corresponding to the end of the branch electrode 14 so that the distance between the external electrode 12 and the auxiliary auxiliary electrode 13 can be increased. Therefore, creeping discharge is not easy to occur. However, recently users have asked the excimer lamp to increase the illuminance, and the luminaire requires a higher input voltage. Therefore, even with the above-mentioned conventional configuration, the creeping discharge X generated by the auxiliary electrode 13 will still follow the branch electrode. 1 4 reaches the external electrode 1 2, and affects the regular discharge between the external electrodes 12. According to the composition of the prior art, to avoid this problem, the branch electrode 14 can be extended for a longer distance in the tube axis direction, but this will make the overall length of the lamp longer, comprehensively considering the effective luminous length, which is not practical. The price is unacceptable. [PRIOR ART DOCUMENT] [Patent Document 1] Japanese Laid-Open Patent Publication No. Hei. No. Hei. No. Hei. No. Hei. In view of the problems of the prior art, the present invention provides an excimer lamp which is provided on at least one of the outer surfaces of the discharge vessel and has one pair of external electrodes having light transmittance, and the inner surface of the discharge vessel is disposed An excimer lamp formed by starting an auxiliary electrode, characterized in that a branch electrode having the longest possible creeping distance is disposed in a limited space, so that the creeping discharge generated by the starting auxiliary electrode is transmitted along the branch electrode without reaching The external electrode does not affect the regular discharge between the external electrodes of 201237925. [Means for Solving the Problems] In the present invention, in the above-described aspect, the branch electrode is formed by the end portion of the root portion and the branch portion forming portion electrode in the axial direction along the branch portion of the discharge vessel. The starter auxiliary electrode of the tip end of the root portion facing the discharge vessel is disposed so as to overlap at least one of the branch tips of the outer electrode. Further, the root portion of the branch electrode is characterized in that one end portion in the width direction of the pole extends in the tube axis direction, and the tip end of the root portion faces the width direction of the discharge vessel, and is characterized by the root connecting portion of the branch electrode. The width is larger than the width of the aforementioned branches. Further, it is characterized in that the width of the other portion of the branch portion of the branch portion of the branch electrode is large. [Effect of the Invention] According to the present invention, the root portion extending in the direction of the branch axis of the external electrode and the branch electrode of the branch extending along the width and the branch tip of the branch electrode are initially along the branch Pass it out. On the other hand, in the gap portion on the straight path from the front to the outer electrode, no surface charge does not accumulate and no potential is formed. Therefore, the outer electrode is provided with a branch, and the root portion extends from the outer tube axis direction, and the width direction Extending; the dendritic electric system of the partial electrode extends from the other end portion from the external electric branch. The width of the tip end portion of the branch portion and the electrode portion is formed by the tube. Therefore, the auxiliary surface electrode is activated at the surface of the electrode, and the electrode is not produced in the direction of the glass inner gap portion. A creeping discharge occurs in the direction of the external electrode. Further, the root portion of the dendritic electrode extends from one end portion in the width direction of the end portion of the external electrode, so that the length of the branch portion is maximized, the total length of the branch electrode is increased, and the creeping discharge can be surely prevented from reaching the external electrode. . Further, the connecting portion of the root portion and the branch portion has a wider width than the branch portion of the branch electrode, so that a connecting portion having a wider area in the electrode portion accumulates more electric charges. Thereby, the creeping discharge which is initially generated between the auxiliary electrode and the tip end of the branch is directed to the direction in which the charge is accumulated in a large amount, and is more easily transmitted along the branch. Furthermore, the width of the tip end portion of the branch portion of the branch electrode is increased, so that the inner surface of the glass is more likely to accumulate charge between the auxiliary electrode and the wider end portion, and the initial surface is more likely to occur. Discharge. This initial creeping discharge is transmitted along the branches as described above, so that the creeping discharge does not occur in the straight path between the auxiliary electrode and the external electrode. Thereby, it is possible to increase the distance of the creeping discharge without increasing the total length of the lamp, so that it does not reach the external electrode, and does not adversely affect the regular discharge between the external electrodes, which is an effect thereof. [Embodiment] As shown in Fig. 1, in the discharge vessel 2 of the excimer lamp 1 of the present invention, a pair of light transmissive external electrodes 3, 3 are disposed on opposite sides of the discharge vessel 2. As shown in detail in the subsequent figures of Fig. 2, the end portions of the external electrodes 3 are provided with a slightly L-shaped branch electrode 4. The branch electrode 4 is composed of a root portion 5 and a branch portion 6 -9 - 201237925 extending along the outer electrode 3 at one end in the width direction of the discharge vessel 2 in the tube axis direction, and the branch portion 6 is from the root portion The leading end of 5 extends toward the other end side in the width direction of the discharge vessel 2. In particular, as shown in Fig. 3 of the cross section taken along line A-A in Fig. 2, or as shown in Fig. 5, in which only the branched electrode and the auxiliary electrode are taken out, the inner surface of the discharge vessel 2 is provided with a starting auxiliary electrode 7 made of a conductive material. The start auxiliary electrode 7 is interposed between the tip end portion 6a of the branch portion 6 of the branch electrode 4 and the discharge vessel 2, and is disposed to overlap each other. In the above configuration, when the excimer lamp is activated, the high-frequency current applied to one of the external electrodes 3 forms a capacitive coupling state, and passes through the dielectric wall constituting the discharge vessel 2, so that the high-frequency current flows to the other side. The external electrode 3 makes it easy to discharge and improve the startability. At this time, the branch electrode 4 connected to the external electrode 3 has a slightly L-shaped shape. The electric charge accumulated in the auxiliary electrode 7 is generated along the portion where the branch electrode 4 is formed, that is, along the branch portion 6, and then the root portion is followed by the root portion. 5 moving 'by moving along the long path so as not to reach the external electrode 3 ° and start the shortest path between the auxiliary electrode 7 and the external electrode 3 'the branch electrode does not exist' during which no charge occurs. Since it moves, it is difficult to generate creeping discharge between the auxiliary electrode 7 and the external electrode 3. More specifically, when the lamp is activated, 'the inside of the glass tube (the discharge vessel 2) facing the branch 6 of the branch electrode 4 accumulates a charge' forming potential 〇 the auxiliary electrode 7 and the tip end portion 6a of the aforementioned branch portion 6 The glass overlaps each other, and the distance between them is very small 'so that a strong electric field is generated' and a creeping discharge occurs along this portion of -10-201237925. After the discharge here is completed, the discharge is continued between the start auxiliary electrode 7 and the branch portion 6 in the order of the movement of the branch portion 6 toward the root portion 5. That is, the creeping discharge that occurs occurs along the branch portion 6 of the branch electrode 4. On the other hand, between the tip end portion 6a of the branch portion 6 of the branch electrode 4 and the external electrode 3, there is no branch electrode that connects the two to form a short circuit, so that the inner surface of the glass does not accumulate charge and does not form a potential. . Therefore, in the direction in which the auxiliary auxiliary electrode 7 and the external electrode 3 are connected in the straight line, no electric field is generated on the surface of the glass, and creeping discharge does not occur in the direction of the external electrode 3. In the other embodiment, the width of the connecting portion 8 between the root portion 5 of the branch electrode 4 and the branch portion 6 is larger than the width of the branch portion 6. According to this configuration, the connection portion 8 having a large area accumulates a large amount of electric charges, so that the electric field in the direction of the connection portion 8 of the auxiliary electrode 7 and the branch portion 6 is increased, so that the auxiliary electrode 7 and the tip end portion 6a of the branch portion 6 are activated. The creeping discharge that occurs between them is more likely to move in the direction of the connecting portion 8. Therefore, it is possible to prevent the creeping discharge from the branch portion 6 of the branch electrode 4 directly toward the external electrode 3. Further, as shown in Fig. 7, another embodiment, the tip end portion 6a of the branch portion 6 of the branch electrode 4 The width is larger than the width of the other portion of the portion. Thus, the tip portion 6a accumulates a large amount of electric charge, so that the creeping discharge is more likely to occur between the portion and the auxiliary auxiliary electrode 7, preventing the starting auxiliary electrode 7 from facing the external electrode. 3 Discharge occurred. Further, in the above-described embodiment, the root portion 5 of the branch electrode 4 extends from one end portion in the width direction of the external electrode 3 in the tube axis direction, but does not necessarily have to be accurately extended from one end portion as long as it is at the end portion in the width direction. On, can be adapted -11 - 201237925 when choosing a location. In this case, the length of the branch portion 6 extending in the width direction of the L-shaped shape of the branch electrode 4 is compared with the branch electrode 14 of the prior art shown in FIG. 9, even if the full length of the discharge vessel 2 is not changed. , can still increase the distance transmitted by the surface discharge. However, as shown in the above embodiment, it is preferable that the root portion 5 of the branch electrode 4 extends from one end portion in the width direction of the outer electrode 3 to increase the length of the branch portion 6 to the maximum. Further, the boot auxiliary electrode 7 is shown as being overlapped with the branch electrodes 6 and 6 of the pair of external electrodes 3 and 3, but it is not necessary to overlap the two, or may overlap only one of the branch electrodes 6. The configuration is just the same as the prior art 1 described above. In addition, one of the external electrodes 3 is a light transmissive electrode, but the external electrode on the light emitting surface side of the discharge vessel may be light transmissive, and the external electrode on the other side may not have light transmissivity. It is also called a plate electrode. As described above, the excimer lamp of the present invention is provided at the end of the light-transmitting external electrode on the outer surface of the discharge vessel, and is provided with a branch electrode formed by the root portion and the branch portion, and is activated on the inner surface of the discharge vessel. The electrode is disposed at a tip end of the branch electrode of the at least one of the external electrodes, and overlaps with the surface electrode to cause a creeping discharge occurring between the start auxiliary electrode and the tip end of the branch to move along the branch, so that the discharge does not face to the outside The direction of the electrodes is straight, and does not adversely affect the regular discharge between the external electrodes. -12- 201237925 [Simplified description of the drawings] [Fig. 1] A perspective view of an excimer lamp of the present invention. FIG. 2 is a plan view of FIG. 1. FIG. FIG. 3 is a cross-sectional view taken along line A-A of FIG. 2. FIG. Fig. 4 is a cross-sectional view taken along line B-B of Fig. 2; Fig. 5 is a schematic view showing the relationship between the branch electrode and the start auxiliary electrode in Fig. 1. Fig. 6 is a partial plan view of another embodiment. Fig. 7 is a partial plan view of another embodiment. [Fig. 8] A plan view (A) of a conventional technique and a sectional view (B) thereof. [Fig. 9] A plan view of another conventional technique. [Description of main component symbols] 1 : Molecular lamp 2 : Discharge capacitor 3 : External electrode 4 : Branch electrode 5 : Root 6 : Branch 6a : Tip end 7 : Start auxiliary electrode 8 : Connection portion 1 1 : Discharge capacitor 1 2 : External electrode-13- 201237925 1 3 : Start auxiliary electrode 14: Branch electrode X: creeping discharge-14-