Why Light Come Out From The Edge Between Two Walls And Appear Some Black Points On Walls ?

I am doing a blueprint project but I find some unknown error of lighting and incorrect shadow.

My project is a normal apartment. However, I find the light come out from the edge between two walls and appear some black points on walls after building.
I find some methods on the internet and I create a new level to try them. I just import walls, celling and floor to the empty level.

According this UE4 post :
I create an second UV map for lighting in 3ds Max and set suggest value that I circle below.

My value is 512x512 and grid size is 1/512=0.00195312

And the follow is my UV map.

I also set the light map resolution to 1024 in UE4 but the problem still here.

Below is my level. I try to import walls one by one before. However, the problem appear so I try to attach all walls to one object so it may be no space between two walls. Unfortunately, the light
still come out from edge (show below).

I also try to attach roof to walls but problem still here. The level just have two objects, roof+walls and floor but the light still can come out. You can see the light from top edge near roof. Light come
out from same place in two tests.

However, I found that the wrong lights will appear when I use Sky Light. I use Directional Light with Sky Light in all my levels. The following picture is just include Directional Light.
Those error light is gone but the black points are worse.

Would anyone can fix it? Thx

There’s a bunch of issues here
First issue–you have too many things as a single object, looks like you have most of the building as a single object which won’t give good lighting results because it’s too much surface area. Next thing is that you will need a floor that matches the inside outline exactly, rather than using a plane that goes across the entire floor. When you have parts that extend underneath the walls, there will be shadow there and since it won’t match exactly where the wall is, you will get bleeding from the shadows inside the building. For the walls, split off the walls by each room so that you can get more lightmap coverage. Remove the tops and the bottoms of the wall, the bottom is covered by the ground and the top will be covered by the roof so you don’t need polygons there. For the inside around the windows/doors you need to unwrap those by hand, for the lightmaps it works best if the UV islands are similar in size, so you don’t want a bunch of small islands with big islands because it will require you to increase the lightmap resolution enough for the small objects.

Thanks for your suggestion and I will correct them later. I understand the first three point.

  1. split off the wall by each room
  2. delete top and bottom face of walls
  3. don’t just use a single plane for floor of the building

However, I am not really understand the last point that about lightmap. UV island is mean the area of grid in UV editor or every part of UV that I unwrap for the model?
If the meaning is the second one, is it mean every part of UV need similar size?

Also, I want to ask one more question. You said don’t include many model in single object because too much surface area which won’t give good lighting results. Is it mean all objects that I want to import in UE4 need split off them part by part?
Such as door, do I need import it by frame, handle and door these three part?
Even the table, do I need import it by desktop and table legs?

A UV island is like a single piece in the UV map, (it’s like an island). When you have very small islands you have to increase the lightmap resolution otherwise those parts can end up smaller than a pixel and it will look bad. Ideally you have islands of similar size. What can help is to create your UV mapping where small parts are attached to large parts whenever possible. Using Automatic Flatten UV’s will often create small islands.

For props, like a table, keep it all together, rarely would a prop need to be split up. You can reuse props over and over so you want that as a single object. For a door, if the door needs to be animated then the door itself needs to be one object and the handle can be another (since it needs to rotate). If not, then I would have the door frame as one object and the door and handle together. For animated doors you might create the door as a Skeletal Mesh instead of a Static Mesh.

Thank your important and useful suggestion.
I understand the meaning and I try your suggestion that about wall and floor. Then, the light come out from wall edge is solved. However, we can’t solve the black point on the wall because I don’t really know the detail step of UV edit.

You can see below.

In the image, those islands are not scale to same size but I will do it later because I have two questions.
1, Why I reset the UV size and grid size but the grids’ quantity that show on the UV are not change?
2, When I scale those islands to same size, do I need to snap island’s edge and vertex on the UV’s grid edge and vertex correctly?

I wouldn’t worry about the UV grid, since objects aren’t likely to line up to the grid naturally and any curved objects simply can’t line up anyways I think it’s mostly a waste of time to try and line it up with everything.

In your case, in the updated UV’s, you need to increase the size of those objects, there’s a lot of empty space. You can also put a UV seam in the middle of the large island at the bottom so that you can use even more of the space. Another issue will also be those thin islands in the upper left corner, I would select all of the small objects and make them bigger–though they won’t be to scale, it won’t be much of an issue and it will allow you to get away with a lower lightmap resolution. Since you have all of those walls, I would use a 512 or 1024 resolution lightmap.