Static lighting for dynamic objects is stored in lighting samples placed automatically by the lightmass process. These are only placed above surfaces in LightmassImportanceVolumes so the first thing you need to do is to make sure you have one of those.
To reduce flickering and to mask the fact that these samples are quite sparsely placed they are quite heavily interpolated. If you happen to have a brighter area nearby, for example on the floor below, the engine might be blending in some of those samples.
Try turning on Show > Visualize > Volume Light Samples in your viewport to see the placement of these samples. For detailed small interiors there might be too few of them. If this is the case you can lower the value for volume light sample placement in your lightmass settings to something below 1.0. Be careful not to go too far as this will increase both build times and memory usage.