diff --git a/src/pipe/modules/filmsim/main.comp b/src/pipe/modules/filmsim/main.comp
index 2150b4b0..fe6f4719 100644
--- a/src/pipe/modules/filmsim/main.comp
+++ b/src/pipe/modules/filmsim/main.comp
@@ -62,6 +62,11 @@ int binom(inout uint seed, int n, float p)
 #endif
 }
 
+float envelope(float w)
+{
+  return smoothstep(380.0, 400.0, w)*(1.0-smoothstep(700.0, 730.0, w));
+}
+
 vec3 thorlabs_filters(float w)
 {
   // this is what looks like it might be a good fit to the thorlabs filters in a plot.
@@ -212,11 +217,14 @@ void main()
       float lambda = 380 + l*10;
       // float lambda = 380 + l*10 + mrand(seed)*10;
       float val = sigmoid_eval(coeff, lambda);
+      // not sure if needed: cuts off wavelength ranges that the spectral
+      // upsampling doesn't care about since it is outside the XYZ support
+      float env = envelope(lambda);
       tc.x = (l+0.5)/256.0;
       vec3 log_sensitivity = texture(img_filmsim, tc).rgb;
       vec3 sensitivity = pow(vec3(10.0), log_sensitivity);
       sensitivity = mix(sensitivity, vec3(0.0), isnan(sensitivity));
-      raw += sensitivity * val / 40.0; // XXX uh something number of bins * 10nm or something
+      raw += sensitivity * val * env / 40.0; // XXX uh something number of bins * 10nm or something
     }
     // TODO: the following two require to split the kernel and blur the intermediates:
       // TODO gaussian blur / lens radius