diff --git a/Window.py b/Window.py
index 67fd452..43cf01c 100755
--- a/Window.py
+++ b/Window.py
@@ -120,7 +120,7 @@ class Window(object):
             delta = datetime.now() - self.flash_start_dt
             delta_msec = delta.seconds * 1000 + delta.microseconds / 1000
             period = delta_msec / float(self.conf['flash_rate'])
-            mix = (math.sin(math.pi * 2 * period) + 1.0) / 2.0
+            mix = (1.0 - math.cos(math.pi * 2 * period)) / 2.0
         else:
             mix = 0
         linear_combination = lambda (x, y): x + (y - x) * mix