When viewing from an appreciable distance, why do lights seem to flicker or alternately be dim and bright...even though they aren't?

What could be the reason? I believe it's got something to do with the AC frequency, at those distances the effect just gets compounded. Can someone put it to rest please? 
When viewing from a distance, lights seem to flicker or alternately be dim and bright, even though they aren't. This is likely due to what is known as "anomalous refraction" [4]. As light travels through the air, it spreads out [3]. When this light passes through an area where the temperature and density vary, the light becomes distorted, causing the flickering effect [4]. This effect can also be seen when looking at headlights a long distance away. The headlights appear dim because the light is spreading out as it travels toward you [3].
The flickering or twinkling effect of lights when observed from a distance is caused by anomalous refraction as light passes through air, schlieren, where temperatures and densities vary [1]. City lights only twinkle from a distance because the light passes through the earth’s atmosphere [2]. The farther the city lights are the more you will see twinkling effect or scintillation, as it passes through different layers of the earth’s atmosphere [2]. Light from a far away source meets many temperature gradients, and the diffraction causes the light intensity to vary [3]. This is the flickering you see [3]. Light from a less distant (or larger) source is less influenced by this effect [3].