I don't think it's needed to multiply by normal length in shader here

src/default_shaders.cpp

@@ -62,7 +62,8 @@ void main()
 
 	for (uint i = 0u; i < num_lights; i++) {
 		vec3 surfaceToLight = lights[i].position - fragPosition;
-		float brightness = dot(normal, surfaceToLight) / (length(surfaceToLight) * length(normal));
+		//float brightness = dot(normal, surfaceToLight) / (length(surfaceToLight) * length(normal));
+		float brightness = dot(normal, surfaceToLight) / length(surfaceToLight);
 		totalBrightness += brightness;
 	}