Double Penumbra

Error: Light-Field has a "double" penumbra. (non MLC)

Somewhere along the filament of the light field lamp two winding have made close contact with each other, with the effect that the filament is somewhat thicker in that "melting" area. In effect that spot emits less light.

This effectively results in TWO focal spots close to each other, each creating its own penumbra!

Nothing you can do about that: replace the bulb!

Usually the lamp fails within a few hour's anyway.