Electrodeless lamp having a narrow gap between a sealed tube and the arc chamber so as to form a consistent cold spot

摘要

An electrodeless high intensity discharge lamp has a light transmissive ceramic arc tube for containing a discharge sustaining medium and a hollow tube member. An excitation coil for causing an arc discharge is situated about the arc tube. The ceramic arc tube includes a first portion for developing the arc discharge therein and a second portion protruding outwardly from the first portion. The hollow tube member is so disposed in the second portion that a space is provided between the inner wall surface of the second portion and the outer wall surface of the hollow tube member. The space is in communication with the interior of the first portion for allowing the medium to be condensed and retained during the lamp operation.