Message misunderstood

hello.
what the meaning of this message -
"Performance Warning No importance volume found and the scene is so large that the automatically synthesized volume will not yield good results. Please add a tightly bounding lightmass importance volume to optimize your scene’s quality and lighting build times.
"
and what should i do?

thank’s

That means that your level is big enough that an automatically placed Light Importance Volume will cause a major performance problems with your lights and shadows in the level.

What you want to do is place a Light Importance Volume in the level and size it to cover the appropriate play area.

More information can be found here:

thank’s you helped me alot.

You’re welcome! Please set my response as the answer, thanks!