Tuesday, 21 February 2017

Split spectrum in Schulthess arcs

It has been evident in many a spotlight display, but in this case it is particularly striking: the other Schulthess arc is completely blue while the other one is predominantly red.

This is not something we see in simulations, where both components are equally coloured. In the blue-red processed image above it looks like these two arcs split the spectrum of parhelia/subparhelia in two.

I have of course no idea what is going on. Below is a more traditional version of the photo with heavily saturated colours. The display was photographed in Rovaniemi on the night of 28/29 November, 2016. 


  1. I have never seen any divergent light halo and there is a very good chance that I will die without it. Still I try to imagine how it works, so I wonder how this display looks in 3D? And an idea from me as an outsider of this magic: what if the Lowitz crystal tilts' two edge phases are dominating the colour split?

  2. Walt's Streelight Halos, which is available in Walt's site, is the best source if you want to get an idea how 3D halos would feel in live situation.

    The display here is mostly a classical 2D display. That's the idea of the spotlight: to make displays that resemble those seen in sunlight. I want to minimize the divergent component by having as tight beam as possible. It is not worth wasting light for 3D halos. If I want to see 3D halos, I go standing under streetlight. The experience is wonderful when the display is good, but then again, once you have seen one display, you have seen them all.

    So I find myself always going for the spotlight, which brings out the details of the display and where many exciting things seem possible. There is a lot of glitter when you stand in the middle of the beam, insane glitter. In photos everything is evened out. Close to beam the display itself is not necessarily so nicely visible, because it is overwhelmed by the glitter (camera still captures the halos very well). At longer distances the glitter settles down and halos come out better. But often the beam is placed so that you can't view the display from far away.

    The thing about the color split is that you don't see it in simulations. So any explanation for it should be something that simulations don't take into account.