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At a party, I took a picture of a pink light beam with an iPhone 8 as shown below enter image description here This picture was very interesting to me because there are two sharp rings of light of different colors: the inner of bright pink which gradually fades out into the outer of bluish-purple.

This reminded me of the optical effect of a halo which can sometimes be observed when looking at the sun or moon, but the reason for these phenomena is due to refraction from light crystals in the air, which is different to what is being observed here (or maybe it is the same).

What causes the effect in the picture (from how the rings are caused to the different colors)?

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What you're showing and discussing is related to at least three different effects, but nowhere among them is chromatic aberration (so the answer by TuringPattern is decidedly wrong).

  1. The most obvious and striking feature seen in your photo is clipped highlights. The lamp is so bright, and the exposure is so high that colors of the brightest parts of the image can't be represented correctly. So too bright colors become clipped. You can see how the colors change in your photo as we scan from the top to the bottom in the following animation:

  1. The next you discuss is the effect of halos around the Sun and the Moon. These are likely the effects like correctly name, caused by the ice crystals in the atmosphere. Another option is the solar aureole, which is due to dust, pollen and other particles present in the atmosphere.

  2. And finally, there's an aureole-like effect that you can see e.g. in the darkness when looking at a street light: it would seem as if there's a glow around the lamp. It's due to diffraction of light on the aperture (pupil) of the eyes. It's similar to the effect seen in the photos taken with high f-number seen e.g. here, but without spikes since human pupils are almost round rather than polygonal.

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  • $\begingroup$ Thank you, this makes sense! $\endgroup$
    – Ashmit Dutta
    Commented Aug 29, 2022 at 13:01
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This is caused by chromatic aberration in the lens of the camera, which is in fact the same effect causing atmospheric halo effects

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  • $\begingroup$ Could you elaborate more? I understand chromatic aberration happens when the edges of a lens is not exactly ideal, leading light to deviate from the focus point. Does this not just make an image blurrier? $\endgroup$
    – Ashmit Dutta
    Commented Aug 8, 2022 at 3:04
  • $\begingroup$ Chromatic aberration is caused by a lens refracting lower wavelengths more strongly than higher ones. There are two types of chromatic aberration: transverse and axial. The effect I think caused this halo is axial aberration: the camera kept one part of the lamp's spectrum focused, which led to lower wavelengths (bluer) having their focal point before the image sensor, and higher wavelengths (redder) behind the image sensor. $\endgroup$
    – TuringPattern
    Commented Aug 8, 2022 at 9:19
  • $\begingroup$ Ok thanks for clearing it up! That makes sense. However, I'll wait till the end of the bounty in case anyone wants to try to give a separate answer. $\endgroup$
    – Ashmit Dutta
    Commented Aug 9, 2022 at 11:42

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