Dimming effect by zero crossing detector and a triac

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Hey
Thanks for the detailed explanations. (I hope) I have better understanding of it now, but again some questions are coming!

void loop() {
  period = period + fadeAmount;
  if ( period >= FADE_MAX) {
      detachInterrupt(digitalPinToInterrupt(INTERRUPT_PIN));
      digitalWrite(TRIAC_PIN, LOW);
  }
  delay(25);
}

In the code above my goal is to achieve a gradual off effect(not gradual on effect), when fading period reaches its maximum the Triac should go off, but it doesn't work as I expect. shouldn't it go high instantly and then gradually goes off? that's what I want but it take some times to go high.

circut
circut811×483 12.8 KB

BTW what should I consider for selecting the resistors and fuses? my loads are just ac bulb/s. thanks