diff --git a/src/main.rs b/src/main.rs
index bb3e4ca..33d986a 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -219,6 +219,10 @@ fn main() -> ! {
 
     let mut switchctrl = switch_control::SwitchControl::<1>::new(8000, 100, SWITCH_PWM_LIMIT);
 
+    // track nano_joules (== nanoVoltAmpereSeconds) generated, for LED flashing
+    let mut nano_joules: u32 = 0;
+    let mut loopcnt_led_y_off = 0;
+
     let mut loopcnt: u64 = 0;
 
     pin_led_r.set_high().unwrap();
@@ -233,8 +237,6 @@ fn main() -> ! {
         });
 
         if systick_received {
-            pin_led_g.set_high().unwrap();
-
             // re-shedule the systick alarm
             critical_section::with(|_cs| unsafe {
                 core::ptr::write_volatile(&mut SYSTICK_FLAG, false);
@@ -277,6 +279,31 @@ fn main() -> ! {
 
             pwr_switch_ch.set_duty(pwmval as u16);
 
+            // Yellow LED flashes for 10 ms whenever 1 Joule has been generated.
+            // This means that it flashes once per second when output power is 1 Watt, and 3 times
+            // per second if output power is 3 Watt.
+            let nano_joules_generated = vout * iout; // * 1 millisecond, implicitely
+            if nano_joules_generated > 0 {
+                nano_joules += nano_joules_generated as u32;
+            }
+
+            // 1000 mV * 1000 mA * 1000 ms = 1 Joule
+            if nano_joules >= 1000000000 {
+                pin_led_y.set_high().unwrap();
+                loopcnt_led_y_off = loopcnt + 10;
+                nano_joules -= 1000000000;
+            }
+
+            if loopcnt == loopcnt_led_y_off {
+                pin_led_y.set_low().unwrap();
+            }
+
+            // Green LED is on in constant-voltage mode and off in MPPT mode.
+            match switchctrl.get_control_mode() {
+                switch_control::ControlMode::ConstantVoltage => {pin_led_g.set_high().unwrap()},
+                switch_control::ControlMode::MPPT            => {pin_led_g.set_low().unwrap()},
+            }
+
             // do not output status data every loop
             match loopcnt % 500 {
                 1 => {
@@ -323,8 +350,6 @@ fn main() -> ! {
 
         logger.process().unwrap();
 
-        pin_led_y.set_high().unwrap();
-
         // save some power as long as no interrupt occurs
         // FIXME: not working yet for some reason
         //cortex_m::asm::wfi();
diff --git a/src/switch_control.rs b/src/switch_control.rs
index da3825a..2964758 100644
--- a/src/switch_control.rs
+++ b/src/switch_control.rs
@@ -1,7 +1,8 @@
 use crate::logger::Logger;
 use heapless::String;
 
-enum ControlMode {
+#[derive(Copy, Clone)]
+pub enum ControlMode {
     MPPT,
     ConstantVoltage
 }
@@ -289,4 +290,9 @@ impl<const T0: i32> SwitchControl<T0>
 
         logger.log(b"\r\n").unwrap();
     }
+
+    pub fn get_control_mode(&self) -> ControlMode
+    {
+        self.mode
+    }
 }