A seal cartridge and barrel manifold seal are provided for use in a subterranean well and in a method to inject fluid, that is initially produced into the well from a subterranean formation or zone, into another subterranean formation or zone. The light source unit 32 includes a plurality of planar light sources 31 arranged along a planar direction. The contacts may be urged into intimate contact with the workpiece by a biasing structure that pulls the contacts tightly against the workpiece. 1 mm and about 10 mm, and each has a surface area no less than about 0.