Liquid sky (effect)
Liquid sky is a popular lighting effect used by clubs and similar venues. It consists of a laser scanning in a flat beam above the head of the crowd; as with most laser displays, for the effect to become apparent the air must be misted by a fog machine. The fog makes the beam of the laser visible, creating a luminous translucent ceiling of light. Air currents and the diffusion of fresh denser fog create a "swirly" or "marbled" effect.
Liquid sky has several advantages over other laser scanning patterns. The most notable one is that the effect can be visible for the entire crowd since you do not need to be "inside" as you would with a tunnel effect. It also avoids the controversial problem of crowd scanning, where the laser beam comes into direct contact with the crowd, possibly causing temporary blindness and sight loss.