Electrodeless low-pressure discharge lamp with plasma channel

An electrodeless low-pressure discharge lamp comprising

• first and second discharge chambers (1, 1'), each of said first and second discharge chambers comprising
• a lamp envelope (1, 1') having a first end portion (9, 9') and a second end portion (10, 10');
• a generally cylindrical element (2) inside said envelope (1), formed with an aperture defining a linear channel (3, 3') from near said first end portion (9) of said envelope to near said second end portion (10) thereof;
• a gas fill sealed in said envelope and extending through said channel (3), and adapted for ionization to form a plasma;
• a cylindrical excitation coil (6, 6') surrounding said envelope (1, 1') and connected to a generator (16, 16') for generating a high-frequency electromagnetic field, said gas fill forming a plasma in response to application of said electromagnetic field;
• each aperture has a substantially smaller diameter than portions (9, 10) of said envelope beyond axial ends of said cylindrical element (2), thereby confining any arc discharge occurring in said plasma to said smaller diameter, and causing radiation from said arc discharge to be preferentially emitted along an optical axis (4) coinciding with said linear channel (3);
• and wherein said channels in said cylindrical elements define respective optical axes (4, 4') extending along a common straight line.