diff --git a/backend/services/led_service.py b/backend/services/led_service.py
index 125061a..b60456c 100644
--- a/backend/services/led_service.py
+++ b/backend/services/led_service.py
@@ -190,25 +190,60 @@ class LEDService:
             step += 1
 
     def _effect_countdown(self, duration: float = 5.0):
-        cfg = self._cfg.get_effect("countdown")
-        c = cfg.color
         n = self._cfg.count
         blank = WS_Color(0, 0, 0)
-        color = WS_Color(c[0], c[1], c[2])
 
-        self._fill(blank)
+        # Mode sombre : rampe progressive avec couleur flash pour stabiliser AWB caméra
+        lux = self._ambient_lux
+        dark_mode = self._cfg.auto_brightness and lux >= 0 and lux < 50
+
+        if dark_mode:
+            flash_cfg = self._cfg.get_effect("capture")
+            fc = flash_cfg.color
+            color = WS_Color(fc[0], fc[1], fc[2])
+            # Brightness cible du flash
+            target_br = 255 if lux < 50 else (int(255 - (lux - 50) / 130 * 135) if lux < 180 else 80)
+            # Rampe : atteindre target_br quand il reste pre_flash_advance secondes
+            ramp_duration = max(0.1, duration - self._cfg.pre_flash_advance)
+            orig_br = self._cfg.brightness
+            logger.info("Countdown mode sombre: rampe 0→%d sur %.1fs puis stable", target_br, ramp_duration)
+            if HAS_WS281X and self._strip:
+                self._strip.setBrightness(0)
+            self._fill(color)
+        else:
+            cfg = self._cfg.get_effect("countdown")
+            c = cfg.color
+            color = WS_Color(c[0], c[1], c[2])
+            self._fill(blank)
+
         t_start = time.time()
         while not self._cmd_event.is_set() and not self._stop_event.is_set():
             elapsed = time.time() - t_start
             ratio = min(elapsed / duration, 1.0)
-            leds_on = int(ratio * n)
-            for i in range(n):
-                self._strip.setPixelColor(i, color if i < leds_on else blank)
-            self._strip.show()
+
+            if dark_mode:
+                # Rampe de 0 → target_br jusqu'à ramp_duration, puis stable à target_br
+                if elapsed < ramp_duration:
+                    br = int(target_br * elapsed / ramp_duration)
+                else:
+                    br = target_br
+                if HAS_WS281X and self._strip:
+                    self._strip.setBrightness(br)
+                    self._strip.show()
+            else:
+                leds_on = int(ratio * n)
+                for i in range(n):
+                    self._strip.setPixelColor(i, color if i < leds_on else blank)
+                self._strip.show()
+
             if ratio >= 1.0:
                 break
             time.sleep(0.04)
 
+        # En mode sombre, restaurer brightness normale (capture le fera aussi, mais par sécurité)
+        if dark_mode and HAS_WS281X and self._strip:
+            self._strip.setBrightness(orig_br)
+
     def _effect_capture(self):
         """Flash photo.
 
@@ -241,15 +276,22 @@ class LEDService:
         if HAS_WS281X and self._strip:
             self._strip.setBrightness(flash_brightness)
 
+        # Le flash démarre pre_flash_advance secondes AVANT la photo.
+        # La durée ON doit couvrir ce délai + la durée d'exposition.
+        # Sinon les LEDs s'éteignent avant que la photo soit prise.
+        effective_on_time = self._cfg.pre_flash_advance + cfg.flash_duration
+
         try:
-            for _ in range(cfg.flashes):
+            for i in range(cfg.flashes):
                 if self._cmd_event.is_set():
                     break
                 self._fill(flash_color)
-                time.sleep(cfg.flash_duration)
+                # Premier flash : durée étendue pour couvrir le délai + expo
+                # Flashs suivants : durée normale (décoratif post-capture)
+                on_time = effective_on_time if i == 0 else cfg.flash_duration
+                time.sleep(on_time)
                 self._fill(off)
-                # Pause inter-flash plus courte que le flash lui-meme
-                if _ < cfg.flashes - 1:
+                if i < cfg.flashes - 1:
                     time.sleep(cfg.flash_duration * 0.4)
         finally:
             # Toujours restaurer la luminosite normale meme en cas d'erreur