Disabling of a zero intensity light clearly visible

I am building a world with a sun that orbits through a day cycle. When the sun goes beneath the horizon I can either (A) have it continue rotating under the world (multiple terrains) at zero intensity or (B) turn it completely off.

If I (A) it I can see the some part of the light moving even at zero intensity.

So I tried:

(B) when I turn the light off (already at zero intensity) there is a clearly visible instant change in the lighting of the terrains.

It is a directional light. There is also ambient light in scene. The steep angles of the terrains clearly show the light when it is parallel to them (same y, distant x for steep; same x, distant y for flat) even though it’s intensity is zero.

???

addition: I can even set a giant plane with cast shadows on that should block the light as it circles under the map and can still see it’s movement very obviously on my terrains (facing up of course), even though it’s at zero intensity…?

You can change the ambient scene lighting by going into Window > Lighting.

Here is a screenshot of the lighting window. I think you might want to change the ambient intensity to 0.
55515-lighting.png

If you bake the ligthing in the scene via lighting settings then it will not change when you turn directional light on off when intensity is 0