How did they do this glow effect in The Blues Brothers?

How did they add the glow around Joliet (Jake) in the gospel scene in The Blues Brothers?

This is the scene:

It is some form of masked double exposure. They often use a mask on the lens or in the camera to block exposure to a section of the film, and then a reverse mask to film the second part of the exposure. They can also use multiple pieces of film to composite a single exposure rather than a double exposure of a single length of film. The original Star Wars films made heavy use of such composited masked shots. (Look up "Film Optical Printing")

Aykroid and Belushi are not in the same shot. They filmed Aykroid pretending to look at Belushi, and then they filmed Belushi, over-exposed with a spotlight on him. Then they combined the two shots.