diff --git a/lib/src/resources/lights.rs b/lib/src/resources/lights.rs
index b0c1799..717e3cb 100644
--- a/lib/src/resources/lights.rs
+++ b/lib/src/resources/lights.rs
@@ -177,4 +177,29 @@ mod tests {
     fn capacity_bounded_by_max_lights() {
         assert!(MAX_LIGHTS >= 1);
     }
+
+    /// Locks the spot sign convention used by the shader: for a surface point that lies on the
+    /// cone axis, the alignment between the "light -> point" direction (`-l`, where `l` points
+    /// from the surface toward the light) and the stored cone axis (`dir_angle.xyz`, from the
+    /// light toward the scene) must be **+1** (full cone), not −1. A regression to the wrong sign
+    /// would make every spot light contribute zero (black cube). Mirrors the WGSL spot loop.
+    #[test]
+    fn spot_cone_axis_alignment_is_positive() {
+        // Spot at (0,0,3), cone axis pointing toward the origin (light -> scene).
+        let light_pos = Vec3::new(0.0, 0.0, 3.0);
+        let surface_point = Vec3::ZERO;
+        let cone_axis = (surface_point - light_pos).normalize(); // (0,0,-1)
+
+        // Shader math: l points surface -> light; the cone test uses -l (light -> point).
+        let l = (light_pos - surface_point).normalize(); // (0,0,1)
+        let to_point = -l; // (0,0,-1)
+        let cone = to_point.dot(cone_axis);
+
+        assert!(
+            (cone - 1.0).abs() < 1e-6,
+            "on-axis point must align with the cone axis (got {cone}); if it is ~-1 the spot sign is wrong"
+        );
+        // Sanity: the buggy expression (dot of l with the axis) would be ~ -1.
+        assert!((l.dot(cone_axis) + 1.0).abs() < 1e-6);
+    }
 }
diff --git a/lib/src/shaders/standard_shader.wgsl b/lib/src/shaders/standard_shader.wgsl
index 395e781..e7a12c5 100644
--- a/lib/src/shaders/standard_shader.wgsl
+++ b/lib/src/shaders/standard_shader.wgsl
@@ -169,15 +169,19 @@ fn fs_main(in: VertexOutput) -> @location(0) vec4<f32> {
     }
 
     // Lumières spot (indices num_directional + num_point..num_directional + num_point +
-    // num_spot). Cône orienté : pénombre lissée entre le demi-angle intérieur (dir_angle.w) et
-    // un liseré extérieur (demi-angle − 0.1 rad), plus atténuation linéaire par rayon.
+    // num_spot). Cône orienté : on teste l'alignement de la direction **de la lumière vers le
+    // point** de la surface (-l, car l pointe de la surface vers la lumière) avec l'axe du cône
+    // (dir_angle.xyz, de la lumière vers la scène). Pénombre lissée entre le demi-angle intérieur
+    // (dir_angle.w) et un liseré extérieur (demi-angle − 0.1 rad), plus atténuation linéaire.
     let spot_base = frame.num_directional + frame.num_point;
     for (var i = spot_base; i < spot_base + frame.num_spot; i++) {
         let to_light = frame.lights[i].position_dir.xyz - in.world_pos;
         let dist = length(to_light);
-        let l = to_light / max(dist, 1e-4);
+        let l = to_light / max(dist, 1e-4); // surface -> lumière
         let ndotl = max(dot(n, l), 0.0);
-        let cone = dot(l, normalize(frame.lights[i].dir_angle.xyz));
+        // direction lumière -> point de la surface = -l ; alignée avec l'axe du cône (dir_angle.xyz).
+        let to_point = -l;
+        let cone = dot(to_point, normalize(frame.lights[i].dir_angle.xyz));
         let cos_inner = frame.lights[i].dir_angle.w;
         let cos_outer = cos_inner - 0.1;
         let spot_factor = clamp((cone - cos_outer) / max(cos_inner - cos_outer, 1e-4), 0.0, 1.0);