Inquiry | Spawner Requirement

[xX_GeekGamerPlaysMC_Xx]

I've been waiting for some of the spawners I've placed on my island for quite some time, and it hasn't spawned a single mob yet. I just wanna ask if there are some requirements that are needed to be followed or applied for spawners to work? I know that one of them is the light level for the hostile mobs. But in general, do they need any other requirements? For example, spawners are needs to have a 3-block-wide free space for them to spawn or something similar?

Hoping that this would be answered by anyone who is knowledgeable with regards to this topic. Thanks for taking the time to read this thread and advance thank you as well to the person/people who'll be able to help out.