Both light and sound can be faded in or out. This provides a softer change than going from something not being there to being totally there all at once. A sharp change rekindles the attention. A progressive change gives us time to adapt to it and can even become an event in itself. There are things in life that we simply have to wait for. Waiting for a long time might make it seem like there’s no movement at all. Perhaps the “technician” is doing a very subtle fade-out of the old and fade-in of the new conditions. Perhaps this moment of change is an event in itself.
Our mind is wired to respond to change and difference with attention. This enables us to adapt to new conditions and helps us survive. Because of the time element involved in live arts, this is an important consideration when composing a piece. Contrast tends to keep the audience attentive. However, if everything is different and changing all the time, this would become the constant and the mind would register sameness as the contrasting element. Routine can turn my attention off. What do I need to break the routine and wake up? Is it a routine of sameness or a routine of irregularity? Do I need something extraordinary or, rather, some continuity?