diff --git a/optika/rulings/_rulings.py b/optika/rulings/_rulings.py
index f1771026..e57d344a 100644
--- a/optika/rulings/_rulings.py
+++ b/optika/rulings/_rulings.py
@@ -593,21 +593,43 @@ def efficiency(
         grating, :math:`\lambda` is the free-space wavelength of the incident
         light, and :math:`\theta` is the angle of incidence inside the medium.
         """
+        i = self.diffraction_order
+        d = self.depth
 
-        normal_rulings = self.spacing_(rays.position, normal).normalized
+        spacing = self.spacing_(rays.position, normal)
+
+        L = spacing.length
+        normal_rulings = spacing.normalized
 
         parallel_rulings = normal.cross(normal_rulings).normalized
 
         direction = rays.direction
         direction = direction - direction @ parallel_rulings
 
-        wavelength = rays.wavelength
-        cos_theta = -direction @ normal
         amplitude = np.pi / 2
-        d = self.depth / amplitude
-        i = self.diffraction_order
+        wavelength = rays.wavelength
+        cos_alpha = -direction @ normal
+        # alpha = np.arccos(cos_alpha)
+        # print(f"{alpha.to(u.deg)=}")
+        # sin_theta = np.sin(alpha)
+        # sin_beta = i * wavelength / L - sin_theta
+        # beta = np.arcsin(sin_beta)
+        # print(f"{beta.to(u.deg)=}")
+        # cos_beta = np.cos(beta)
+        # n1 = (1 + cos_beta) / (np.pi)
+        n1 = 1 / amplitude
+
+        cos_theta = optika.materials.snells_law_scalar(
+            cos_incidence=cos_alpha,
+            index_refraction=rays.index_refraction,
+            index_refraction_new=rays.index_refraction + n1,
+        )
+        # cos_theta = cos_alpha
 
-        gamma = np.pi * d / (wavelength * cos_theta)
+        print(f"{cos_theta=}")
+
+        gamma = np.pi * d * n1 / (wavelength * cos_theta)
+        print(f"{gamma=}")
 
         result = np.square(np.sin(np.pi * gamma * u.rad) / (np.pi * (gamma + i)))