Okay I tried dynamic light with gimp, after watching endless videos how to add alpha in gimp here we go. I hope I can help all gimp users outside.
Make sure you have all steps from baki or untraditionalnerd. Thanks to both!
Here it's all about alpha channel in gimp.


1. you have your object you want to lighten in a layer, I used the eye from bakie. Make sure it´s the canvas size 1024*1024 px
2. go to LAYER, MASK and then ADD LAYER MASK

a little window will open and you must choose ALPHA CHANNEL OF THE LAYER

that looks like this in the layer section

3. click on the left window where your object is, you can see the white frame around the selected

4. now the fill tool with the color number 848484 or other grey tones


now that must look like in the pic

5. now go to the layers, right click on this and select APPLY LAYER MASK

6. save it as normally

7. in the warehouse tab you must import the .dds file and looks like this

I hope I had nothing forget and it works for you as well.
I know it's been 84 years, but are there updated links to this explanation? The images are all broken and I would love to see the process!