What is the explanation for this light during a rainbow? I am puzzled by the two clear "beams" of light that I saw during a rainbow.
I think that they are simply filtering sun light rays apparently converging at the antisolar point because of perspective.
However, why they seem to emerge from the bow, and are not seen to the right (in the pic) of it? Has this a relation with the darkness of the Alexander band?
(Indeed it was a double rainbow for most of the duration).

 A: What you are seeing is called Rainbow Spokes/Wheels. There is a proper explanation of this phenomenon in atoptics:

Shadows in the sky appear by perspective effects to converge towards
the antisolar point, which is also the centre of rainbows. When clouds
or dense rain showers shadow the light falling into your rainbow cone
the shadowed raindrops can no longer send the rainbow's rays towards
your eye. The result is one or more dark radial spokes centered on the
antisolar point and making the rainbow sometimes resemble a wagon
wheel. Bright spokes are similar to anticrepuscular rays except that
light is directed into specific directions by large raindrops rather
than widely scattered by dust and aerosols.
Sometimes, when clouds are moving fast across the sky, the rainbow
wheel appears to rotate.
The brightness of the unshadowed areas illustrate nicely just how much
of a rainbow's light is cast inside its rim at deviations larger than
the minimum of the rainbow angle.

Here is a photo of a similar phenomenon captured in Pennsylvania on May 10, 2019, around 6:15 p.m.
