First of all, I think it's obvious that the light can not be produced by a flash, simply because of the shadow of the man: to produce a shadow like this one, the source of light (the flash) must be behind the man, not in his hands!
My first thought was the Heilingeschein, but this phenomena usually fades "slowly", doesn't have the color border shown in the picture. Maybe there is a little of this effect, but just in the centre, around the shadow of Lewin's head. So, I think it's a rainbow; 1) the brighter area inside; 2) the colorful border and the dispoSition of the colors (red on the outside, and blue and violet on the inside), and 3) the darkness outside, these three effects are typical of the rainbow.
It may be caused by a high density of little drops of water between the source of light and the ground, or something that acts in a similar way, maybe with a different angle of refraction. If it's water, it could be artificially produced by a machine in the construction area (i don't think it's natural fog because the shadow has sharp edges, not like in a foggy day). I tried to make this effect yesterday at 13:30 in the south balcony of my house, in Girona (Europe), with a spray of water (the kind you use to vaporize plants or to iron clothes). I stayed with the sun behind me, and vaporized in front of me. The result is a round rainbow around my shadow, not an arc but a complete circle, just interrupted by the shadow of my own legs. Yesterday, in Girona, at 42ºN (just like Boston, Massachussets), at 13:30 (local time), this circular rainbow was "floating" in the low front of me. If I wanted it on the ground (just like the picture of Lewin), I think I should wait until summer equinox, when the sun is higher, and even bend myself a little, like doing a reverence.
There is a second possibility: the rainbow is not produced by waterdorps, but by another spherical medium (don't know which one). This would explain the size of the circle, that appears smaller than the one I made at home, maybe because of a different angle of diffraction.
Montse Bosch