diff --git a/pyTSEB/net_radiation.py b/pyTSEB/net_radiation.py
index 9c0292b..3e83a07 100644
--- a/pyTSEB/net_radiation.py
+++ b/pyTSEB/net_radiation.py
@@ -42,7 +42,11 @@
 
 import pyTSEB.meteo_utils as met
 
-
+#==============================================================================
+# List of constants used in the netRadiation Module
+#==============================================================================
+# Stephan Boltzmann constant (W m-2 K-4)
+sb = 5.670373e-8
 TAUD_STEP_SIZE_DEG = 5