Mobs will rarely spawn when there is no light source nearby, even if it is the only place for mobs to spawn. If a player places a torch on the ground, nearby dark areas will start to spawn mobs.

Steps to Reproduce:

1. Boot Minecraft 1.14.4 Java edition.
2. Proceed to an open field with a wide-open space and no light sources nearby.
3. Wait until night time.
4. Throughout the night, make a note of how many mobs are spawning around you.
5. During the next day, place a torch nearby.
6. Throughout the next night, again make a note of how many mobs are spawning around you.

Results:

Notably fewer mobs will have spawned when there are no light sources nearby compared to when the torch has been placed.

Rate of Reproduction:

2/3