hi theo, been talking to the mathematician behind that paper on knots, he explained that the "null condition" is where the EM field is... zero, and that the E is perpendicular to M at all points. it's not the same thing as the "non-radiating condition" for which you have to take a fourier transform.

he sent a link to the above paper which he said may have some clues about non-radiating conditions.

l.