Hi folks!
Don’t know if I missing something here but whenever I made a change in my level and decided to save it as another file such as level01,the build data is gone and I should build the whole lighting again. How can I keep the previous data without baking again?
When you do a ‘save as’, you’re creating a new level. Then you have to build light on that level.
Yes but little have changed in the scene.I don’t want to do whole building again.I just want a version of the scene with some small changes not a whole new level
Even if you move one object, all the light has to be rebuild I’m afraid. That’s how it works.
What if I don’t want to, or the object is dynamic.There should be an option! 
If the object is dynamic, it’s no problem. It’s only changes that give you the red ‘lighting needs to be rebuilt ( x objects )’ message.
my problem is not that red error message. Thing is when I save as the level, Light build data completely gone and shadows gets completely black as there is no gi.
Not sure I’m afraid. Try logging the question on answerhub ( it’s on the community menu ).
have you found a way to save as or duplicate a level without losing baked light data?
found a way…just copy the entire project in another directory of your computer, open it and change the name of the level you want to duplicate, after that, migrate the level to your original project, leaving only selectet the level itself and its “map build data registry”