diff --git a/src/xyz/marsavic/gfxlab/graphics3d/scene/SpectrumTest.java b/src/xyz/marsavic/gfxlab/graphics3d/scene/SpectrumTest.java
index b7e509b..b7fa3fe 100644
--- a/src/xyz/marsavic/gfxlab/graphics3d/scene/SpectrumTest.java
+++ b/src/xyz/marsavic/gfxlab/graphics3d/scene/SpectrumTest.java
@@ -45,7 +45,9 @@ public class SpectrumTest extends Scene.Base {
                 HalfSpace.pn(Vec3.xyz( 0,  0,  1), Vec3.xyz( 0,  0, -1), materialUVWalls),
 
                 Ball.cr(Vec3.xyz(-0.3,  0.3,  0.0), 0.4, uv -> Material.GLASS.refractive(w->0.5)),
-                Ball.cr(Vec3.xyz( 0.4, -0.4,  0.0), 0.4, uv -> Material.GLASS)
+                Ball.cr(Vec3.xyz( 0.4, -0.4,  0.0), 0.4, uv -> Material.GLASS.refractiveIndex(
+                        w -> 2.6 + (w-400)/(800-400) * (1.55 - 2.6)
+                ))
 //                Ball.cr(Vec3.xyz(-0.3, -0.4, -0.6), 0.4, uv -> Material.GLASS.refractiveIndex(w -> 2.5)),
 //                Ball.cr(Vec3.xyz( 0.4,  0.3,  0.6), 0.4, uv -> Material.GLASS.refractiveIndex(w -> 0.6))
         );