diff --git a/usermods/SN_Photoresistor/usermod_sn_photoresistor.h b/usermods/SN_Photoresistor/usermod_sn_photoresistor.h
index 465b22f7..3fd1fafa 100644
--- a/usermods/SN_Photoresistor/usermod_sn_photoresistor.h
+++ b/usermods/SN_Photoresistor/usermod_sn_photoresistor.h
@@ -2,7 +2,7 @@
 
 #include "wled.h"
 
-//Pin defaults for QuinLed Dig-Uno
+//Pin defaults for QuinLed Dig-Uno (A0)
 #define PHOTORESISTOR_PIN A0
 
 // the frequency to check photoresistor, 10 seconds
@@ -38,6 +38,12 @@
 class Usermod_SN_Photoresistor : public Usermod
 {
 private:
+  float referenceVoltage = USERMOD_SN_PHOTORESISTOR_REFERENCE_VOLTAGE;
+  float resistorValue = USERMOD_SN_PHOTORESISTOR_RESISTOR_VALUE;
+  float adcPrecision = USERMOD_SN_PHOTORESISTOR_ADC_PRECISION;
+  int8_t offset = USERMOD_SN_PHOTORESISTOR_OFFSET_VALUE;
+
+  unsigned long readingInterval = USERMOD_SN_PHOTORESISTOR_MEASUREMENT_INTERVAL;
   // set last reading as "40 sec before boot", so first reading is taken after 20 sec
   unsigned long lastMeasurement = UINT32_MAX - (USERMOD_SN_PHOTORESISTOR_MEASUREMENT_INTERVAL - USERMOD_SN_PHOTORESISTOR_FIRST_MEASUREMENT_AT);
   // flag to indicate we have finished the first getTemperature call
@@ -46,6 +52,18 @@ private:
   bool getLuminanceComplete = false;
   uint16_t lastLDRValue = -1000;
 
+  // flag set at startup
+  bool disabled = false;
+
+  // strings to reduce flash memory usage (used more than twice)
+  static const char _name[];
+  static const char _enabled[];
+  static const char _readInterval[];
+  static const char _referenceVoltage[];
+  static const char _resistorValue[];
+  static const char _adcPrecision[];
+  static const char _offset[];
+
   bool checkBoundSensor(float newValue, float prevValue, float maxDiff)
   {
     return isnan(prevValue) || newValue <= prevValue - maxDiff || newValue >= prevValue + maxDiff;
@@ -55,8 +73,8 @@ private:
   {
     // http://forum.arduino.cc/index.php?topic=37555.0
     // https://forum.arduino.cc/index.php?topic=185158.0
-    float volts = analogRead(PHOTORESISTOR_PIN) * (USERMOD_SN_PHOTORESISTOR_REFERENCE_VOLTAGE / USERMOD_SN_PHOTORESISTOR_ADC_PRECISION);
-    float amps = volts / USERMOD_SN_PHOTORESISTOR_RESISTOR_VALUE;
+    float volts = analogRead(PHOTORESISTOR_PIN) * (referenceVoltage / adcPrecision);
+    float amps = volts / resistorValue;
     float lux = amps * 1000000 * 2.0;
 
     lastMeasurement = millis();
@@ -67,23 +85,27 @@ private:
 public:
   void setup()
   {
+    // set pinmode
     pinMode(PHOTORESISTOR_PIN, INPUT);
   }
 
   void loop()
   {
+    if (disabled || strip.isUpdating())
+      return;
+
     unsigned long now = millis();
 
     // check to see if we are due for taking a measurement
     // lastMeasurement will not be updated until the conversion
     // is complete the the reading is finished
-    if (now - lastMeasurement < USERMOD_SN_PHOTORESISTOR_MEASUREMENT_INTERVAL)
+    if (now - lastMeasurement < readingInterval)
     {
       return;
     }
 
     uint16_t currentLDRValue = getLuminance();
-    if (checkBoundSensor(currentLDRValue, lastLDRValue, USERMOD_SN_PHOTORESISTOR_OFFSET_VALUE))
+    if (checkBoundSensor(currentLDRValue, lastLDRValue, offset))
     {
       lastLDRValue = currentLDRValue;
 
@@ -104,7 +126,8 @@ public:
   void addToJsonInfo(JsonObject &root)
   {
     JsonObject user = root[F("u")];
-    if (user.isNull()) user = root.createNestedObject(F("u"));
+    if (user.isNull())
+      user = root.createNestedObject(F("u"));
 
     JsonArray lux = user.createNestedArray(F("Luminance"));
 
@@ -125,4 +148,63 @@ public:
   {
     return USERMOD_ID_SN_PHOTORESISTOR;
   }
+
+  /**
+     * addToConfig() (called from set.cpp) stores persistent properties to cfg.json
+     */
+  void addToConfig(JsonObject &root)
+  {
+    // we add JSON object.
+    JsonObject top = root.createNestedObject(FPSTR(_name)); // usermodname
+    top[FPSTR(_enabled)] = !disabled;
+    top[FPSTR(_readInterval)] = readingInterval / 1000;
+    top[FPSTR(_referenceVoltage)] = referenceVoltage;
+    top[FPSTR(_resistorValue)] = resistorValue;
+    top[FPSTR(_adcPrecision)] = adcPrecision;
+    top[FPSTR(_offset)] = offset;
+
+    DEBUG_PRINTLN(F("Photoresistor config saved."));
+  }
+
+  /**
+     * readFromConfig() is called before setup() to populate properties from values stored in cfg.json
+     */
+  void readFromConfig(JsonObject &root)
+  {
+    // we look for JSON object.
+    JsonObject top = root[FPSTR(_name)];
+
+    if (!top.isNull())
+    {
+      if (top[FPSTR(_enabled)].is<bool>())
+      {
+        disabled = !top[FPSTR(_enabled)].as<bool>();
+      }
+      else
+      {
+        String str = top[FPSTR(_enabled)]; // checkbox -> off or on
+        disabled = (bool)(str == "off");   // off is guaranteed to be present
+      };
+
+      readingInterval = min(120, max(10, top[FPSTR(_readInterval)].as<int>())) * 1000; // convert to ms
+      referenceVoltage = top[FPSTR(_referenceVoltage)].as<float>();
+      resistorValue = top[FPSTR(_resistorValue)].as<float>();
+      adcPrecision = top[FPSTR(_adcPrecision)].as<float>();
+      offset = top[FPSTR(_offset)].as<int>();
+      DEBUG_PRINTLN(F("Photoresistor config (re)loaded."));
+    }
+    else
+    {
+      DEBUG_PRINTLN(F("No config found. (Using defaults.)"));
+    }
+  }
 };
+
+// strings to reduce flash memory usage (used more than twice)
+const char Usermod_SN_Photoresistor::_name[] PROGMEM = "Photoresistor";
+const char Usermod_SN_Photoresistor::_enabled[] PROGMEM = "enabled";
+const char Usermod_SN_Photoresistor::_readInterval[] PROGMEM = "read-interval-s";
+const char Usermod_SN_Photoresistor::_referenceVoltage[] PROGMEM = "supplied-voltage";
+const char Usermod_SN_Photoresistor::_resistorValue[] PROGMEM = "resistor-value";
+const char Usermod_SN_Photoresistor::_adcPrecision[] PROGMEM = "adc-precision";
+const char Usermod_SN_Photoresistor::_offset[] PROGMEM = "offset";
\ No newline at end of file