displays are a particularly spectacular form of reflected artificial luminance that has become commonplace over the past two decades. They are now regularly used at big celebrations or public events (e.g. rock shows, festivals, opening of new clubs etc.).

A computer controls the sequence of firing and rotation as powerful lasers beam skyward. These bounce off clouds to create oval/tadpole shapes which circle one another, swoop inward and perform a “sky dance”. Alternatively, they can be perceived as a “dark spinning disc” with white lights “running around its edge”, or simply as a rotating “ring” composed of many lights.

They are so powerful you can see some of the effect up to 50 km (30 miles) away if the prevailing cloud-base is fairly high.