diff --git a/firmware/apps/buggy.c b/firmware/apps/buggy.c
index e04d436..080b5ea 100644
--- a/firmware/apps/buggy.c
+++ b/firmware/apps/buggy.c
@@ -13,7 +13,7 @@ static void init(void) {
 static void run(void) {
 	uint16_t light = photons_measure();
 
-	pentatonic_all_led_set(light >> 7);
+	pentatonic_all_led_set(light >> 3);
 
 	wait_ms(500);
 }
diff --git a/firmware/include/pentabug/photons.h b/firmware/include/pentabug/photons.h
index ff2b5cd..b2cd2ce 100644
--- a/firmware/include/pentabug/photons.h
+++ b/firmware/include/pentabug/photons.h
@@ -5,6 +5,6 @@
 
 void photons_init(void);
 
-uint16_t photons_measure(void);
+uint8_t photons_measure(void);
 
 #endif /* PHOTONS_H */
diff --git a/firmware/lib/photons.c b/firmware/lib/photons.c
index 498236c..20653f0 100644
--- a/firmware/lib/photons.c
+++ b/firmware/lib/photons.c
@@ -5,9 +5,11 @@
 #include <pentabug/hal.h>
 #include <pentabug/lifecycle.h>
 
-void photons_init(void) {}
+void photons_init(void) {
+	ADCSRA |= (1 << ADEN);
+}
 
-uint16_t photons_measure(void) {
+uint8_t photons_measure(void) {
 	// save old state
 
 	uint8_t old_port = PORTC;
@@ -18,34 +20,40 @@ uint16_t photons_measure(void) {
 	led_off(RIGHT);
 	led_off(LEFT);
 
-	// set direction, no pullups
+	// set to ground for discharge
 
-	DDRC &= ~(1 << 3);
 	PORTC &= ~(1 << 3);
 
 	// wait for discharge
-	// TODO: needed?
 
-	wait_ms(10);
+	wait_ms(1);
+
+	// set direction to input for measurement
+
+	DDRC &= ~(1 << 3);
+
+	// collect some photons
+
+	wait_ms(1);
 
 	// start measurement
 
-	ADMUX  = (1 << REFS0);
-	ADCSRA = (1 << ADPS2) | (1 << ADPS1);
-	ADCSRA |= (1 << ADEN);
+	ADMUX  = (1 << REFS0) | (1 << ADLAR);
+	ADCSRA |= (1 << ADPS2) | (1 << ADPS1);
 
 	ADMUX = (ADMUX & ~(0x1F)) | 3;
+
 	ADCSRA |= (1 << ADSC);
 
 	// wait for measurement to finish
 
 	while (ADCSRA & (1 << ADSC)) test_stop_app();
 
-	uint16_t res = ADCW;
+	uint8_t res = ADCH;
 
 	// disable adc
 
-	ADCSRA &= ~(1 << ADEN);
+	/*ADCSRA &= ~(1 << ADEN);*/
 
 	// restore state