Multiple refraction pattern?

Can anyone give a background flavour, not full mathematics, behind this
phenomenon.

http://home.graffiti.net/diverse:graffiti.net/tripoly.jpg

The even, arc of light in the top 2 superimposed pics, that emanates from
the single source street light shown in lowest pic section 3. The intensity
in the arc is fairly even but it it is strongest in line of direct view but
that direct view is not obviously a streetlight as the image is not broader
at that point, just a bit brighter.
An exterior lean-to roof with a street light about 50m away.
Ignore the other odd lights and reflections and camera lens artefact.
The roof is made from triple polycarbonete *** in a cell sructure, like
this www pic
http://www.brettmartin.com/images/polycarbonateadvert.gif




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