diff --git a/main.c b/main.c
index 4e770d3..ca85578 100644
--- a/main.c
+++ b/main.c
@@ -96,8 +96,17 @@ uint8_t command_i = 0;
 uint8_t gamma_correction_lut[256] = {0};
 /** photo-resistor measurement of ambient luminosity */
 volatile uint16_t photoresistor_value = 0;
+/** photo-resistor voltage for the minimum brightness */
+#define PHOTORESISTOR_MIN 2.7
+/** photo-resistor voltage for the maximum brightness */
+#define PHOTORESISTOR_MAX 1.7
 /** factor to dim LED of the clock, depending on the ambient luminosity */
 float clock_brithtness = 0;
+/** minimum LED brightness */
+#define BRIGHTNESS_MIN 0.2
+/** maximum LED brightness */
+#define BRIGHTNESS_MAX 1.0
+
 
 int _write(int file, char *ptr, int len)
 {
@@ -493,20 +502,19 @@ int main(void)
 				rtc_set_counter_val(rtc_get_counter_val()%ticks_midday); // reset time counter
             }
 			clock_set_time(rtc_get_counter_val()); // set time
-			//adc_start_conversion_regular(ADC1); // start measuring ambient luminosity
 		}
 		while (photoresistor_flag) { // new photo-resistor value has been measured
 			photoresistor_flag = false; // reset flag
 			action = true; // action has been performed
 			float photoresistor_voltage = photoresistor_value*1.2/ref_value; // calculate voltage from value
-			if (photoresistor_voltage<1.7) { // high ambient luminosity
-				clock_brithtness = 1; // set highest brightness
-			} else if (photoresistor_voltage>2.1) { // low ambient luminosity
-				clock_brithtness = 0.3; // set low brightness
+			if (photoresistor_voltage<PHOTORESISTOR_MAX) { // high ambient luminosity
+				clock_brithtness = BRIGHTNESS_MAX; // set highest brightness
+			} else if (photoresistor_voltage>PHOTORESISTOR_MIN) { // low ambient luminosity
+				clock_brithtness = BRIGHTNESS_MIN; // set low brightness
 			} else { // intermediate ambient luminosity
-				clock_brithtness = 0.3+(0.7*(1-(photoresistor_voltage-1.7)/0.4)); // set variable brightness
+				clock_brithtness = BRIGHTNESS_MIN+(BRIGHTNESS_MAX-BRIGHTNESS_MIN)*(1-(photoresistor_voltage-PHOTORESISTOR_MAX)/(PHOTORESISTOR_MIN-PHOTORESISTOR_MAX)); // set variable brightness
 			}
-			//printf("%f, %f\n", photoresistor_voltage, clock_brithtness);
+			printf("%f, %f\n", photoresistor_voltage, clock_brithtness);
 		}
 		if (action) { // go to sleep if nothing had to be done, else recheck for activity
 			action = false;