Set initial led value

cpdctrl/measurement.py

@@ -94,8 +94,12 @@ def measure(
     if flush_after == 0: flush_after = None
     try:
         i = 0
-        led_val = None
-        led_script.start()
+        led_val = led_script.start()
+        try:
+            led_dev.set_level(led_val)
+        except Exception as e:
+            log.error(f"Error setting led to {led_val:03}%: {e}")
+            raise e
         t_iter_start = time.time()
         while True:
             # using while True and if, to be able to log the stop reason