diff --git a/light9/Effects.py b/light9/Effects.py
--- a/light9/Effects.py
+++ b/light9/Effects.py
@@ -18,7 +18,7 @@ def register(f):
 @register
 class Strip(object):
     """list of r,g,b tuples for sending to an LED strip"""
-    which = 'L'
+    which = 'L' # LR means both
     pixels = []
     @classmethod
     def solid(cls, which='L', color=(1,1,1)):
diff --git a/light9/effecteval/effectloop.py b/light9/effecteval/effectloop.py
--- a/light9/effecteval/effectloop.py
+++ b/light9/effecteval/effectloop.py
@@ -186,7 +186,8 @@ class LedLoop(EffectLoop):
             elif isinstance(out, Effects.Strip):
                 pixels = numpy.array(out.pixels, dtype=numpy.float16)
                 px255 = (numpy.clip(pixels, 0, 1) * 255).astype(numpy.uint8)
-                combined[out.which] = numpy.maximum(combined[out.which], px255)
+                for w in out.which:
+                    combined[w] = numpy.maximum(combined[w], px255)
                 
         return combined