I converted a single player map to 19w14a. The building was in darkness despite having a lot of torches , jack o lanterns in it.

There were mobs spawned in the house due to lack of light.

They list on f3 as showing light but don't actually produce light until you have placed a lantern near them. The picture shows the torches before and after placing a lantern near them. As you can see form the insert, the torches further back are not producing light.