Cloud brightness varies depending on how much sunlight is scattered back to your eye.
Here's a breakdown of the factors influencing cloud brightness, based on available information:
- Water Particle Density: Thicker clouds, with more water particles, scatter more sunlight, making them appear brighter. Conversely, thin clouds have fewer water particles, resulting in less scattering and a dimmer appearance. As the reference states, "If you are looking at a thin cloud, then there are few water particles to scatter the light, so the cloud will not look bright white."
In essence, the brightness of a cloud depends on how much of the sun's energy is reflected towards the observer. A cloud's thickness, determined by its water particle density, directly influences this reflection.
