Questions about using pictures as lighting

Hi all , hope this is the right spot to ask for help , I want to be able to use a picture to overlay over the map to add extra lighting like sun beams coming from windows and street lamps shining bright , stuff like that , I'm finding it hard to find the best way to create a picture of right size for each of the maps , I have an example picture added , for some reason It's just confusing me how to get each maps size correct so they fit on the screen properly , I looked on youtube to see if anyone did a tutorial video but they are all for MV and other makers.

 

In rpgmaker 2k / 2k3 1 tile is 16X16 pixels
multiply the map size by 16 to get the actual pixel size
example:
20X15=>(20*16)X(15*16)=>320X240 pixels

 

Use this Maps converter in a PNG file:
https://forums.rpgmakerweb.com/index.php?threads/map-exporting-to-png-image.90264/