What is the critical requirement regarding particle size for observing distinct, bright bands of color in cloud iridescence?

Answer

The water droplets or ice crystals must be nearly identical in size.

The uniformity of the particles is key; if the water droplets or ice crystals are nearly identical in size, they scatter the light coherently, resulting in distinct bands of color. Variation leads to a washed-out appearance.

What is the critical requirement regarding particle size for observing distinct, bright bands of color in cloud iridescence?
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