These are just some ideas to expand on the linked guide. Credit to @I-am-helpful for the guide.
Continuing the discussion from How to make a room dark | Difficulty : 
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[Follow the guide above]
Guide Modification 1: Making a Map Dark
The barrier can actually be sized indefinitely so make the first step to size it as large as possible, to your map size.
Guide Modification 2: Tinting a Large Area
You can manipulate a border to show a different color. Here’s how:
Set your border color to any color you want. This can be used to simulate lighting. Tada, you just made lighting different.