The minecraft glowing item frame is being affected by the blockface dimming feature.
It isn't being rendered the same way as a minecraft light source block should be. eg. Glowstone Block.

Steps to Reproduce

1. Place a block in the air where all sides of that block are visible/not blocked by any other block.
2. Place a glow_frame on each side of the block. (On top of it, under it & all the sides)
3. (Optional) Place a filled map in all of the glow frames for better visibility of the issue.

Observed Results

The glow frame & the map/item being displayed inside it are darkened depending on which side of the block they're placed on. On the top of the block there is no blockface dimming. But on the sides & the bottom, they are slighly darker than on the top, and at them bottom it's the most.

Glow frames have "face_dimming" setting in the "material_instances" set to "true" in the block's behavior json file, even though it's a glow frame.

Expected Behavior

Glow frame's "face_dimming" setting should be set to "false", since it's a glow frame so it should have similar render properties like a glowstone block, or any other light source. Just the differnece being that it doesn't emmit actual light.