For some of the high powered LED lights, the beam seems to have bright and dimmer sections along its length when projected through air.
They seem to be regularly spaced rather than random. Some people have described it as looking as though the beam would get thinner and wider along its length.
It was not observed (noticed) for HID beams for example...just for high powered LED.
What would be an explanation for that?
Off hand, I wondered if it were some sort of resonance/harmonic between the emitter frequencies and the media or wavelength of the light?