diff --git a/homeassistant/components/pilight/light.py b/homeassistant/components/pilight/light.py
index 12d175817d7..11eeb02293e 100644
--- a/homeassistant/components/pilight/light.py
+++ b/homeassistant/components/pilight/light.py
@@ -61,7 +61,20 @@ class PilightLight(PilightBaseDevice, LightEntity):
 
     def turn_on(self, **kwargs):
         """Turn the switch on by calling pilight.send service with on code."""
-        self._brightness = kwargs.get(ATTR_BRIGHTNESS, 255)
-        dimlevel = int(self._brightness / (255 / self._dimlevel_max))
+        # Update brightness only if provided as an argument.
+        # This will allow the switch to keep its previous brightness level.
+        dimlevel = None
+
+        if ATTR_BRIGHTNESS in kwargs:
+            self._brightness = kwargs[ATTR_BRIGHTNESS]
+
+            # Calculate pilight brightness (as a range of 0 to 15)
+            # By creating a percentage
+            percentage = self._brightness / 255
+            # Then calculate the dimmer range (aka amount of available brightness steps).
+            dimrange = self._dimlevel_max - self._dimlevel_min
+            # Finally calculate the pilight brightness.
+            # We add dimlevel_min back in to ensure the minimum is always reached.
+            dimlevel = int(percentage * dimrange + self._dimlevel_min)
 
         self.set_state(turn_on=True, dimlevel=dimlevel)