animation – How to use a normal map for light effects with an AnimatedSrpite?

I am trying to add light effects with normal map on an AnimatedSprite. I was following that tutorial but with no success.

I am using a Ligth2D, this sprite sheet:

enter image description here

and have created a shader on Material to apply the normal map with this code:

shader_type canvas_item;

uniform sampler2D normal_map;

void fragment(){
    NORMAL = 2.0 * texture(normal_map, UV).rgb - 1.0;

enter image description here

Here is the result:

enter image description here

One can observe a light reflection on the left upper of the hourglass, but the light is neither smooth nor consistant.

NB: I have made the spirte sheet myself, feel free to use it.