Cattle have excellent night vision. You don't have to leave a light on for them.
That makes sense, in nature nobody stands with a lamp near the animals. With luck, the moonlight is the only light source.
During a "night barn check", it is useful for the farmer if there is night lighting.
He sees less in the dark than his cattle!
Cattle cannot perceive the color red.
A red light source with a light intensity <5 Lux is sufficient for the farmer to see. Cows experience this as dark.
Lux is the number of lumens per square meter (lx = lm / m²).