From 737f23a0bdb8a1c09bb0dee9709d09cb4c5403c4 Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@koston.org>
Date: Mon, 24 Nov 2025 10:23:11 -0600
Subject: [PATCH] [light] Dynamically disable loop when idle to reduce CPU
 overhead (#11881)

---
 esphome/components/light/light_state.cpp | 24 ++++++++++++++++++++++++
 esphome/components/light/light_state.h   |  3 +++
 2 files changed, 27 insertions(+)

diff --git a/esphome/components/light/light_state.cpp b/esphome/components/light/light_state.cpp
index 36b2af03a..9cde9077d 100644
--- a/esphome/components/light/light_state.cpp
+++ b/esphome/components/light/light_state.cpp
@@ -23,6 +23,9 @@ void LightState::setup() {
     effect->init_internal(this);
   }
 
+  // Start with loop disabled if idle - respects any effects/transitions set up during initialization
+  this->disable_loop_if_idle_();
+
   // When supported color temperature range is known, initialize color temperature setting within bounds.
   auto traits = this->get_traits();
   float min_mireds = traits.get_min_mireds();
@@ -125,6 +128,9 @@ void LightState::loop() {
       this->is_transformer_active_ = false;
       this->transformer_ = nullptr;
       this->target_state_reached_callback_.call();
+
+      // Disable loop if idle (no transformer and no effect)
+      this->disable_loop_if_idle_();
     }
   }
 
@@ -132,6 +138,8 @@ void LightState::loop() {
   if (this->next_write_) {
     this->next_write_ = false;
     this->output_->write_state(this);
+    // Disable loop if idle (no transformer and no effect)
+    this->disable_loop_if_idle_();
   }
 }
 
@@ -227,6 +235,8 @@ void LightState::start_effect_(uint32_t effect_index) {
   this->active_effect_index_ = effect_index;
   auto *effect = this->get_active_effect_();
   effect->start_internal();
+  // Enable loop while effect is active
+  this->enable_loop();
 }
 LightEffect *LightState::get_active_effect_() {
   if (this->active_effect_index_ == 0) {
@@ -241,6 +251,8 @@ void LightState::stop_effect_() {
     effect->stop();
   }
   this->active_effect_index_ = 0;
+  // Disable loop if idle (no effect and no transformer)
+  this->disable_loop_if_idle_();
 }
 
 void LightState::start_transition_(const LightColorValues &target, uint32_t length, bool set_remote_values) {
@@ -250,6 +262,8 @@ void LightState::start_transition_(const LightColorValues &target, uint32_t leng
   if (set_remote_values) {
     this->remote_values = target;
   }
+  // Enable loop while transition is active
+  this->enable_loop();
 }
 
 void LightState::start_flash_(const LightColorValues &target, uint32_t length, bool set_remote_values) {
@@ -265,6 +279,8 @@ void LightState::start_flash_(const LightColorValues &target, uint32_t length, b
   if (set_remote_values) {
     this->remote_values = target;
   };
+  // Enable loop while flash is active
+  this->enable_loop();
 }
 
 void LightState::set_immediately_(const LightColorValues &target, bool set_remote_values) {
@@ -276,6 +292,14 @@ void LightState::set_immediately_(const LightColorValues &target, bool set_remot
   }
   this->output_->update_state(this);
   this->next_write_ = true;
+  this->enable_loop();
+}
+
+void LightState::disable_loop_if_idle_() {
+  // Only disable loop if both transformer and effect are inactive, and no pending writes
+  if (this->transformer_ == nullptr && this->get_active_effect_() == nullptr && !this->next_write_) {
+    this->disable_loop();
+  }
 }
 
 void LightState::save_remote_values_() {
diff --git a/esphome/components/light/light_state.h b/esphome/components/light/light_state.h
index 06519cdc1..ad8922b46 100644
--- a/esphome/components/light/light_state.h
+++ b/esphome/components/light/light_state.h
@@ -255,6 +255,9 @@ class LightState : public EntityBase, public Component {
   /// Internal method to save the current remote_values to the preferences
   void save_remote_values_();
 
+  /// Disable loop if neither transformer nor effect is active
+  void disable_loop_if_idle_();
+
   /// Store the output to allow effects to have more access.
   LightOutput *output_;
   /// The currently active transformer for this light (transition/flash).