diff --git a/README.md b/README.md
index 17eb81f..260196e 100644
--- a/README.md
+++ b/README.md
@@ -12,6 +12,8 @@
 * usb phone charger as power supply
 * 2 push buttons
 * 1 on/off switch
+* 1 photoresistor
+* 1 resistor to make secund shoulder of photosensitive "bridge", 10 kOhms, 0.25 watts
 * Gainta G521G enclosure (92x66.5x28мм)
 * 5m power cord
 
diff --git a/clock_schem.pdf b/clock_schem.pdf
index ef901b3..cf05b18 100644
Binary files a/clock_schem.pdf and b/clock_schem.pdf differ
diff --git a/simpleclock.ino b/simpleclock.ino
index eb1ecbe..1f3f920 100644
--- a/simpleclock.ino
+++ b/simpleclock.ino
@@ -61,6 +61,10 @@ bool dot = true;
 
 /* time inaccuracy compensation flag */
 uint8_t compflag = 0;
+const uint8_t timeSkew = 6; // assume that clock runs faster than should
+
+/* ambient light compensation aka night mode */
+const int photoPin = A2;
 
 void setup()
 {
@@ -70,7 +74,12 @@ void setup()
 	byte digitPins[] = {9, 10, 11, 12};
 	byte segmentPins[] = {2, 3, 4, 5, 6, 7, 8, 13};
 	bool resistorsOnSegments = true; // 8 resistors, 330 Ohms each
-	bool updateWithDelays = false;   // Default. Recommended
+        /* updateWithDelays defaults to false and it is recommended value,
+	 * but i was unable to make my display to change brightness with
+	 * recommended value, so i have to use updateWithDelays=true,
+	 * in this case brightness gets changed.
+	 */
+	bool updateWithDelays = true;   // Default. Recommended
 
 	/* without it there is visual bug at 0 o'clock, and in current version
 	 * of SevSeg' setChars() does not dots at all */
@@ -96,6 +105,9 @@ void setup()
 	// setup control buttons
 	pinMode(hrs_btn, INPUT_PULLUP);
 	pinMode(min_btn, INPUT_PULLUP);
+
+	// setup brigtness sensor
+	pinMode(photoPin, INPUT);
 }
 
 void loop()
@@ -104,6 +116,7 @@ void loop()
 	currentPushTimer = currentMillis;
 	char str[4];
 	float d;
+	unsigned int ambLight = analogRead(photoPin);
 
 	clock.getTime();
 
@@ -162,7 +175,7 @@ void loop()
 
 	if ((clock.hour == 21) and (clock.minute == 21) and
             (clock.second == 21) and (compflag == 0)) {
-		clock.fillByHMS(clock.hour, clock.minute, 14);
+		clock.fillByHMS(clock.hour, clock.minute, (clock.second - timeSkew));
 		clock.setTime();
 		compflag = 1;
 	}
@@ -191,6 +204,31 @@ void loop()
 		}
 	}
 
+	/* ambient light compensation
+	 * ambLight can be in range of 0..1023, if it 800, it has point to use fullbright
+	 */
+	if (ambLight >= 940) {
+		Display.setBrightness(100);
+	} else if ((ambLight < 900) and (ambLight >= 840)) {
+		Display.setBrightness(95);
+	} else if ((ambLight < 800) and (ambLight >= 735)) {
+		Display.setBrightness(70);
+	} else if ((ambLight < 700) and (ambLight >= 635)) {
+		Display.setBrightness(25);
+	} else if ((ambLight < 600) and (ambLight >= 530)) {
+		Display.setBrightness(15);
+	} else if ((ambLight < 500) and (ambLight >= 430)) {
+		Display.setBrightness(12);
+	} else if ((ambLight < 400) and (ambLight >= 325)) {
+		Display.setBrightness(10);
+	} else if ((ambLight < 300) and (ambLight >= 220)) {
+		Display.setBrightness(8);
+	} else if ((ambLight < 200) and (ambLight >= 110)) {
+		Display.setBrightness(7);
+	} else if (ambLight < 100) {
+		Display.setBrightness(6);
+	}
+
 	Display.refreshDisplay();
 }