I was watching this slow motion video of an underwater explosion (1:03 - 1:15) and I noticed that at the beginning of the explosion, it gives off light, then as the sphere of the blast expands the light fades away, but then as the sphere of the blast collapses again the light returns. Why does this happen?
I was only able to come up with one shaky hypothesis: that there might be light tricks going on with the way that the light is refracted by the shape of the sphere, so makes it look like the light fading out, when in actuality it is just being refracted away from the camera.
Of course I am no expert in this and I look forward to being proven wrong.