UV Maps needed for lightmaps?

I am just trying to understand lightmap creation…
Is it absolutely essential that I have at least one UV map channel for lightmap channel creation?
So first UV unwrapping then lightmap?

Unreal will create a default lightmap based on the uv unwrap you have for the mesh but it isnt ideal. In the mesh editor you will notice up top a drop down button that says UV channel 0. click that and it will show you that there is a channel 0 and 1. 0 is your texture channel and 1 is your lightmap that unreal created. Under the details panel and static mesh settings click on the little down arrow to expand that section and you will see lightmap index and it will say 1. This means that it is using channel 1 for the light map. For example if you have several uv channels for a mesh and you needed to specify which one was the light map this is where you would change that.
Sometimes you will notice strange shadows when using dynamic lighting. So your best option is to create a second uv map in your 3d program so that you can control exactly which way the uv islands are facing.
I uploaded a little snap shot of everything I mentioned here.

Hi sesamkorn,

Yes, it is recommended to use a set of UVs (usually channel 1) for your lightmap. There is documentation provided by epic on UV layouts for Unreal here:


If you are don’t want to make a unique UV channel you can set the Source Lightmap Index to 0 to use your initial UV Channel just be aware that you need evenly Laid out UVs and they cannot overlap.


Thank you, I got it!