You merely adopted it

- Default light to 0 in DefaultVertexList
- Take the max of mesh and instance light in the instance shader

common/src/lib/java/dev/engine_room/flywheel/lib/vertex/DefaultVertexList.java

@@ -1,7 +1,6 @@
 package dev.engine_room.flywheel.lib.vertex;
 
 import dev.engine_room.flywheel.api.vertex.MutableVertexList;
-import net.minecraft.client.renderer.LightTexture;
 import net.minecraft.client.renderer.texture.OverlayTexture;
 
 public interface DefaultVertexList extends MutableVertexList {
@@ -57,7 +56,7 @@ default int overlay(int index) {
 
 	@Override
 	default int light(int index) {
-		return LightTexture.FULL_BRIGHT;
+		return 0;
 	}
 
 	@Override

common/src/lib/resources/assets/flywheel/flywheel/instance/oriented.vert

@@ -6,5 +6,5 @@ void flw_instanceVertex(in FlwInstance i) {
     flw_vertexColor *= i.color;
     flw_vertexOverlay = i.overlay;
     // Some drivers have a bug where uint over float division is invalid, so use an explicit cast.
-    flw_vertexLight = vec2(i.light) / 256.0;
+    flw_vertexLight = max(vec2(i.light) / 256.0, flw_vertexLight);
 }

common/src/lib/resources/assets/flywheel/flywheel/instance/posed.vert

@@ -4,5 +4,5 @@ void flw_instanceVertex(in FlwInstance i) {
     flw_vertexColor *= i.color;
     flw_vertexOverlay = i.overlay;
     // Some drivers have a bug where uint over float division is invalid, so use an explicit cast.
-    flw_vertexLight = vec2(i.light) / 256.0;
+    flw_vertexLight = max(vec2(i.light) / 256.0, flw_vertexLight);
 }

common/src/lib/resources/assets/flywheel/flywheel/instance/transformed.vert

@@ -4,5 +4,5 @@ void flw_instanceVertex(in FlwInstance i) {
     flw_vertexColor *= i.color;
     flw_vertexOverlay = i.overlay;
     // Some drivers have a bug where uint over float division is invalid, so use an explicit cast.
-    flw_vertexLight = vec2(i.light) / 256.0;
+    flw_vertexLight = max(vec2(i.light) / 256.0, flw_vertexLight);
 }