If you disable the upscaling toggle when deferred technical preview is enabled the lighting glitches around light sources or player as shown in the pictures below.

Steps to reproduce:

1. Download the mcpack file from the attachments.
2. Import the mcpack file.
3. Create a new world with creative mode(survival is fine)
4. When creating the world make sure to turn on the experiment renderdragon features for creators
5. Enable the mcpack in the world setting when creating the world
6. Create the world.
7. Enable the deferred technical preview in the video settings
8. Turn off the upscaling
9. Place a soul lantern or a torch and break it
10. Fly 2 or 3 blocks up from where you broke the soul lantern