Shrimp stay buried in deeper water with muddy or sandy bottom during the daytime to avoid predators and light.
They move up onto the flats at night to feed where they can hide in the vegetation. At night the vegetation gives off oxygen that is the byproduct of transpiration.
Shrimp don't like light but they like the increased oxygen levels in plant life.
Shrimp have eyes that are designed to see in a certain range of light levels. Very low light levels as a matter of fact. That is the reason why their eyes glow when you shine a light on them because of the reflective coating in the back of their eyes that help amplify light. Their eyes adjust to light levels much more slowly than humans do.
The polychaetes, nematodes, algae, and vegetable matter they feed on do the same thing. Ever notice how your depthfinder screen looks more cluttered after dark. That is phytoplankton moving up in the water column off the bottom. The lights you use don’t attract shrimp they just help you see them better.
Shrimp are structure oriented like fish so they will move along and around things in the water like the bottom, channel edges, your anchor rope, your boat, or your lights. They come to the surface for several other reasons.
Fish chase them from below because their silhouettes are easier to see against the sky than against the bottom at night. Turbulence from the uneven bottom creates upwelling’s that push them up in certain places. The shrimp you see at the surface are only part of the shrimp going past you with the current. The barometer will also have an effect. Higher barometric pressure increases the dissolved oxygen levels near the surface making it more comfortable near the surface. Lower barometric pressure decreases dissolved oxygen levels near the surface making it less comfortable for them. Moving water has more oxygen at the surface than still water.