Have seen it about 2-3 times in the mighty TriMotor crossing the ITCZ en route to Ascension.
Looked like the windshield turned into one of those plasma balls with purple "Lightning" effects all over it. Seemed to pulse, possibly due to the heating elements embedded in the panes.
Scared me witless when I first saw it
Didn't feel alot better about it when I saw it again!