diff --git a/crates/ui-egui/src/i18n/ui.rs b/crates/ui-egui/src/i18n/ui.rs
index 434f2b79..c0b61996 100644
--- a/crates/ui-egui/src/i18n/ui.rs
+++ b/crates/ui-egui/src/i18n/ui.rs
@@ -294,7 +294,6 @@ const JAPANESE: &[(&str, &str)] = &[
     ("Latest auto-save: {}", "最新の自動保存：{}"),
     ("Layer", "レイヤー"),
     ("Layer controls", "レイヤーコントロール"),
-    ("Layer {}", "レイヤー{}"),
     ("Layer:", "レイヤー:"),
     ("Layer: {}", "レイヤー：{}"),
     ("Layer Styles", "レイヤースタイル"),
@@ -1029,7 +1028,6 @@ const SIMPLIFIED_CHINESE: &[(&str, &str)] = &[
     ("Latest auto-save: {}", "最新的自动保存：{}"),
     ("Layer", "图层"),
     ("Layer controls", "图层控制"),
-    ("Layer {}", "图层 {}"),
     ("Layer:", "图层："),
     ("Layer: {}", "图层：{}"),
     ("Layer Styles", "图层样式"),
@@ -1769,7 +1767,6 @@ const TRADITIONAL_CHINESE: &[(&str, &str)] = &[
     ("Latest auto-save: {}", "最新的自動儲存：{}"),
     ("Layer", "圖層"),
     ("Layer controls", "圖層控制"),
-    ("Layer {}", "圖層 {}"),
     ("Layer:", "圖層："),
     ("Layer: {}", "圖層：{}"),
     ("Layer Styles", "圖層樣式"),
@@ -2512,7 +2509,6 @@ const UKRAINIAN: &[(&str, &str)] = &[
     ("Latest auto-save: {}", "Останнє автозбереження: {}"),
     ("Layer", "Шар"),
     ("Layer controls", "Керування шарами"),
-    ("Layer {}", "Шар {}"),
     ("Layer:", "Шар:"),
     ("Layer: {}", "Шар: {}"),
     ("Layer Styles", "Стилі шару"),
@@ -3070,7 +3066,6 @@ const PORTUGUESE: &[(&str, &str)] = &[
     ("Latest auto-save: {}", "Último salvamento automático: {}"),
     ("Layer", "Camada"),
     ("Layer controls", "Controles da camada"),
-    ("Layer {}", "Camada {}"),
     ("Layer:", "Camada:"),
     ("Layer: {}", "Camada: {}"),
     ("Layer Styles", "Estilos de camada"),
@@ -3529,7 +3524,6 @@ const CZECH: &[(&str, &str)] = &[
     ("Latest auto-save: {}", "Nejnovější automatická záloha: {}"),
     ("Layer", "Vrstva"),
     ("Layer controls", "Ovládací prvky vrstvy"),
-    ("Layer {}", "Vrstva {}"),
     ("Layer:", "Vrstva:"),
     ("Layer: {}", "Vrstva: {}"),
     ("Layer Styles", "Styly vrstvy"),
@@ -4092,7 +4086,6 @@ const SPANISH: &[(&str, &str)] = &[
     ("Latest auto-save: {}", "Último guardado automático: {}"),
     ("Layer", "Capa"),
     ("Layer controls", "Controles de capa"),
-    ("Layer {}", "Capa {}"),
     ("Layer:", "Capa:"),
     ("Layer: {}", "Capa: {}"),
     ("Layer Styles", "Estilos de capa"),
diff --git a/crates/ui-egui/src/panels/effect_controls.rs b/crates/ui-egui/src/panels/effect_controls.rs
index 03b3a1ac..f930aff2 100644
--- a/crates/ui-egui/src/panels/effect_controls.rs
+++ b/crates/ui-egui/src/panels/effect_controls.rs
@@ -441,19 +441,10 @@ fn prop_row(
             let comp = app.session.active_comp_arc();
             if let Some(comp) = comp {
                 let dr = Rect::from_min_size(pos2(vx, cy - 9.0), vec2(((r.max.x - vx) * 0.55).clamp(90.0, 170.0), 18.0));
-                let idx_of = |id: u64| comp.layers.iter().position(|x| x.id.0 == id);
-                let name = l.and_then(|id| idx_of(id).map(|i| format!("{}. {}", i + 1, comp.layers[i].name))).unwrap_or_else(|| "None".into());
-                let pop = egui::Id::new(("ec-lpop", uid));
-                if widgets::dropdown(ui, dr, &name, &t, egui::Id::new(("ec-l", uid))).clicked() {
-                    widgets::open_popup(ui, pop);
+                if let Some(chosen) = widgets::layer_picker(ui, dr, &comp.layers, *l, &t, egui::Id::new(("ec-l", uid))) {
+                    set(actions, chosen.map(|id| json!(id)).unwrap_or(serde_json::Value::Null));
                 }
                 app.auto.add(&format!("effectControls.prop.{uid}.value"), dr, &prop.name);
-                let mut opts = vec!["None".to_string()];
-                opts.extend(comp.layers.iter().enumerate().map(|(i, l)| format!("{}. {}", i + 1, l.name)));
-                let cur = l.and_then(idx_of).map(|i| i + 1).unwrap_or(0);
-                if let Some(i) = widgets::popup_menu(ui, pop, dr.left_bottom(), &opts, Some(cur)) {
-                    set(actions, if i == 0 { serde_json::Value::Null } else { json!(comp.layers[i - 1].id.0) });
-                }
                 // Source / Masks / Effects & Masks (the hidden companion parameter).
                 if let Some(src) = group.get(&effectcraft_engine::effects::layer_source_id(&prop.match_id)) {
                     let si = src.value.as_enum() as usize;
diff --git a/crates/ui-egui/src/panels/timeline.rs b/crates/ui-egui/src/panels/timeline.rs
index b34fbd9d..a48cc3e4 100644
--- a/crates/ui-egui/src/panels/timeline.rs
+++ b/crates/ui-egui/src/panels/timeline.rs
@@ -4233,13 +4233,16 @@ fn value_editor(
         }
         Value::Text(_) => {}
         Value::Layer(l) => {
-            p.text(
-                pos2(x, at.y),
-                Align2::LEFT_CENTER,
-                l.map(|l| crate::i18n::tr_args("Layer {}", &[&l])).unwrap_or(crate::i18n::tr("None").into()),
-                Tokens::ui(12.0),
-                t.hot_text,
-            );
+            // Layer references (a light's Source, a Displacement Map's layer…) pick from the
+            // comp's layers, as in Effect Controls; the choice is written through the same
+            // undoable prop.set as the other value arms.
+            let r = Rect::from_min_size(pos2(x, at.y - 9.0), vec2(150.0, 18.0));
+            if let Some(comp) = app.session.active_comp_arc()
+                && let Some(chosen) = widgets::layer_picker(ui, r, &comp.layers, *l, &t, egui::Id::new(("tl-lay", uid)))
+            {
+                set(actions, chosen.map(|id| json!(id)).unwrap_or(serde_json::Value::Null));
+            }
+            app.auto.add(&format!("timeline.prop.{uid}.value"), r, &prop.name);
         }
         Value::Gradient(_) => {
             // Opens the Gradient Editor at the current time (#612).
diff --git a/crates/ui-egui/src/widgets.rs b/crates/ui-egui/src/widgets.rs
index c005224d..f74cc048 100644
--- a/crates/ui-egui/src/widgets.rs
+++ b/crates/ui-egui/src/widgets.rs
@@ -557,6 +557,44 @@ pub fn popup_menu(ui: &mut Ui, id: egui::Id, pos: egui::Pos2, options: &[String]
     })
 }
 
+/// The drop-down for a layer-valued property (`ParamUi::Layer`): the current layer shown as
+/// "N. name" (or "None"), and a popup of "None" plus every layer of the comp. Effect Controls
+/// and the Timeline share it so a layer reference (an Environment light's Source, a Displacement
+/// Map's layer) is picked the same way in every panel, and the reference is shown as its layer's
+/// index and name rather than its internal id. Returns `Some(chosen)` when the user picked —
+/// the layer's id, or `None` for "None" — and `None` while nothing is chosen; the caller writes
+/// it as an undoable `prop.set` (id, or null for "None").
+pub fn layer_picker(
+    ui: &mut Ui,
+    rect: Rect,
+    layers: &[effectcraft_engine::project::Layer],
+    current: Option<u64>,
+    t: &Tokens,
+    id: egui::Id,
+) -> Option<Option<u64>> {
+    let index_of = |wanted: u64| layers.iter().position(|l| l.id.0 == wanted);
+    let entry = |i: usize| layers.get(i).map(|l| format!("{}. {}", i + 1, l.name));
+    let current_index = current.and_then(index_of);
+    let label = current_index.and_then(entry).unwrap_or_else(|| crate::i18n::tr("None").to_string());
+    let pop = id.with("pop");
+    if dropdown(ui, rect, &label, t, id).clicked() {
+        open_popup(ui, pop);
+    }
+    if !popup_is_open(ui, pop) {
+        return None;
+    }
+    // Built only while open: a comp can hold hundreds of layers.
+    let mut options: Vec<String> = Vec::with_capacity(layers.len() + 1);
+    options.push(crate::i18n::tr("None").to_string());
+    options.extend((0..layers.len()).filter_map(entry));
+    // The current entry is highlighted (the first option is "None").
+    match popup_menu(ui, pop, rect.left_bottom(), &options, Some(current_index.map_or(0, |i| i + 1))) {
+        Some(0) => Some(None),
+        Some(picked) => layers.get(picked - 1).map(|l| Some(l.id.0)),
+        None => None,
+    }
+}
+
 /// The open popup list `id` at `pos`, drawn by `body` (`rows` entries and `seps` separators,
 /// for its height): as tall as the window allows, scrolling beyond with a scroll bar (a shape
 /// layer's Add menu has 20 entries, the blend modes 40, the fonts hundreds), and moved up when
diff --git a/crates/ui-egui/tests/ui_layer_source_picker.rs b/crates/ui-egui/tests/ui_layer_source_picker.rs
new file mode 100644
index 00000000..9b952de7
--- /dev/null
+++ b/crates/ui-egui/tests/ui_layer_source_picker.rs
@@ -0,0 +1,211 @@
+//! Picking a layer-valued property with the shared drop-down: the Timeline draws a layer-valued
+//! Light Options property (an Environment light's Source) as a drop-down of the comp's layers,
+//! Effect Controls' layer parameters (a Displacement Map's layer) pick through the same widget,
+//! and both write an undoable `prop.set`.
+
+use effectcraft_engine::Session;
+use effectcraft_engine::keyframe::Value;
+use effectcraft_engine::project::LayerId;
+use effectcraft_ui_egui::EffectcraftApp;
+use effectcraft_ui_egui::dock::PanelKind;
+use egui::{Pos2, Rect, pos2, vec2};
+use egui_kittest::Harness;
+use egui_kittest::kittest::NodeT;
+use egui_kittest::kittest::Queryable;
+use serde_json::json;
+
+fn click(h: &mut Harness<'_, EffectcraftApp>, at: Pos2) {
+    h.event(egui::Event::PointerMoved(at));
+    h.step();
+    h.event(egui::Event::PointerButton { pos: at, button: egui::PointerButton::Primary, pressed: true, modifiers: Default::default() });
+    h.step();
+    h.event(egui::Event::PointerButton { pos: at, button: egui::PointerButton::Primary, pressed: false, modifiers: Default::default() });
+    h.run_steps(3);
+}
+
+fn rect_of(h: &Harness<'_, EffectcraftApp>, id: &str) -> Rect {
+    let e = h.state().auto.find(id).unwrap_or_else(|| panic!("no automation element {id}")).clone();
+    Rect::from_min_size(pos2(e.rect[0], e.rect[1]), vec2(e.rect[2], e.rect[3]))
+}
+
+/// Whether `want` is painted inside `row` (the drop-down's current-value text).
+fn painted_in(h: &Harness<'_, EffectcraftApp>, row: Rect, want: &str) -> bool {
+    h.output().shapes.iter().any(|c| match &c.shape {
+        egui::Shape::Text(t) => t.galley.text() == want && row.expand(3.0).contains(t.pos),
+        _ => false,
+    })
+}
+
+/// The current value of a layer-valued property, by uid.
+fn layer_value(h: &Harness<'_, EffectcraftApp>, layer: u64, prop: u64) -> Option<u64> {
+    let comp = h.state().session.active_comp().unwrap();
+    match &comp.layer(LayerId(layer)).unwrap().props.find(prop).unwrap().value {
+        Value::Layer(v) => *v,
+        other => panic!("property {prop} is not layer-valued: {other:?}"),
+    }
+}
+
+/// The "N. name" a drop-down shows for a layer.
+fn entry_for(h: &Harness<'_, EffectcraftApp>, layer: u64) -> String {
+    let comp = h.state().session.active_comp().unwrap();
+    let i = comp.layers.iter().position(|l| l.id.0 == layer).unwrap();
+    format!("{}. {}", i + 1, comp.layers[i].name)
+}
+
+/// Puts the layer-valued `prop` of `layer` back to `value` with a direct `prop.set` (no merge key,
+/// so the pick below records its own step instead of folding into a picker write), picks `none`
+/// from the drop-down at `value_id`, and checks the clear takes one undo step that restores `value`.
+#[track_caller]
+fn none_pick_clears(h: &mut Harness<'_, EffectcraftApp>, value_id: &str, none: &str, layer: u64, prop: u64, value: u64) {
+    h.state_mut().session.execute("prop.set", json!({"layer": layer, "prop": prop, "value": value})).unwrap();
+    h.run_steps(2);
+    assert_eq!(layer_value(h, layer, prop), Some(value));
+    let steps = h.state().session.history.undo.len();
+    let at = rect_of(h, value_id).center();
+    click(h, at);
+    h.get_by_label(none).click();
+    h.run_steps(3);
+    assert_eq!(layer_value(h, layer, prop), None, "selecting None clears the value");
+    assert_eq!(h.state().session.history.undo.len(), steps + 1, "one clear undo step");
+    h.state_mut().session.execute("edit.undo", json!({})).unwrap();
+    h.run_steps(2);
+    assert_eq!(layer_value(h, layer, prop), Some(value), "undo restores the selected layer");
+}
+
+/// A light's Source (a layer-valued Light Options property) picks a comp layer from the
+/// Timeline and undo restores None.
+#[test]
+fn timeline_source_drop_down_picks_the_layer_and_undo_restores_none() {
+    let mut s = Session::default();
+    s.execute("comp.new", json!({"name": "Main", "width": 640, "height": 360, "frameRate": 30, "duration": 4})).unwrap();
+    s.execute("comp.settings", json!({"renderer": "advanced3D"})).unwrap();
+    let sky = s.execute("layer.newSolid", json!({"name": "Sky HDRI", "color": "#66aaff"})).unwrap()["layer"].as_u64().unwrap();
+    let light = s.execute("layer.newLight", json!({"kind": "Environment", "name": "Env Light"})).unwrap()["layer"].as_u64().unwrap();
+    let (group, source) = {
+        let comp = s.active_comp().unwrap();
+        let opts = comp.layer(LayerId(light)).unwrap().props.sub("lightOptions").unwrap();
+        (opts.uid, opts.get("source").unwrap().uid)
+    };
+    let mut app = EffectcraftApp::new(s);
+    app.ui.timeline.open_layers.insert(light);
+    app.ui.timeline.open_groups.insert(group);
+    let mut h = Harness::builder().with_size(vec2(1600.0, 1000.0)).build_eframe(|_| app);
+    h.run_steps(4);
+
+    let value_id = format!("timeline.prop.{source}.value");
+    // Unset: the row is a drop-down reading "None" — an element to click, not bare text.
+    assert_eq!(layer_value(&h, light, source), None);
+    assert!(painted_in(&h, rect_of(&h, &value_id), "None"), "the Source row shows a None drop-down");
+
+    // Opening it lists "None" and every layer of the comp, by index and name.
+    let at = rect_of(&h, &value_id).center();
+    click(&mut h, at);
+    let entry = entry_for(&h, sky);
+    assert!(h.query_by_label("None").is_some(), "the list starts with None");
+    assert!(h.query_by_label(&entry).is_some(), "the comp's layers are listed ({entry})");
+
+    let steps = h.state().session.history.undo.len();
+    h.get_by_label(&entry).click();
+    h.run_steps(3);
+    assert_eq!(layer_value(&h, light, source), Some(sky), "the Source holds the layer id");
+    assert_eq!(h.state().session.history.undo.len(), steps + 1, "one undo step");
+    // The row names the layer (index and name), not its internal id.
+    assert!(painted_in(&h, rect_of(&h, &value_id), &entry), "the Source row shows the layer's name");
+
+    // Dismissing the list without choosing writes nothing; reopening marks the chosen layer as
+    // the current entry (and "None" as not current).
+    click(&mut h, pos2(1500.0, 300.0));
+    h.run_steps(2);
+    assert_eq!(layer_value(&h, light, source), Some(sky), "dismissing the list writes nothing");
+    let reopen = rect_of(&h, &value_id).center();
+    click(&mut h, reopen);
+    assert_eq!(h.get_by_label(&entry).accesskit_node().toggled(), Some(egui::accesskit::Toggled::True), "the current entry is highlighted");
+    assert_eq!(h.get_by_label("None").accesskit_node().toggled(), Some(egui::accesskit::Toggled::False), "None is not the current entry");
+    click(&mut h, pos2(1500.0, 300.0));
+    h.run_steps(2);
+
+    h.state_mut().session.execute("edit.undo", json!({})).unwrap();
+    h.run_steps(2);
+    assert_eq!(layer_value(&h, light, source), None, "undo restores None");
+
+    none_pick_clears(&mut h, &value_id, "None", light, source, sky);
+}
+
+/// The shared widget is the one Effect Controls already used: a Displacement Map's layer
+/// parameter still picks from the drop-down and still undoes. The interface language is
+/// Japanese: "None" is the catalog's word there, like every other label drawn in the panel.
+#[test]
+fn effect_controls_layer_param_picks_through_the_shared_widget() {
+    let mut s = Session::default();
+    s.prefs.general.language = "ja".to_string();
+    s.execute("comp.new", json!({"name": "Main", "width": 640, "height": 360, "frameRate": 30, "duration": 4})).unwrap();
+    let map = s.execute("layer.newSolid", json!({"name": "Disp", "color": "#ff0000"})).unwrap()["layer"].as_u64().unwrap();
+    let base = s.execute("layer.newSolid", json!({"name": "Base", "color": "#20c040"})).unwrap()["layer"].as_u64().unwrap();
+    let fx = s.execute("effect.apply", json!({"layers": [base], "effect": "Displacement Map"})).unwrap()["effects"][0].as_u64().unwrap();
+    let prop = {
+        let comp = s.active_comp().unwrap();
+        comp.layer(LayerId(base)).unwrap().effects().unwrap().find_group(fx).unwrap().get("displacementMapLayer").unwrap().uid
+    };
+    s.state.selected_layers = vec![LayerId(base)];
+    let mut app = EffectcraftApp::new(s);
+    app.show_panel(PanelKind::EffectControls);
+    let mut h = Harness::builder().with_size(vec2(1600.0, 1100.0)).build_eframe(|_| app);
+    h.run_steps(4);
+
+    let value_id = format!("effectControls.prop.{prop}.value");
+    // The closed drop-down is the translated "None" (なし), not a hardcoded English word.
+    let row = rect_of(&h, &value_id);
+    assert!(painted_in(&h, row, "なし"), "the parameter row shows the translated None");
+    click(&mut h, row.center());
+    let entry = entry_for(&h, map);
+    assert!(h.query_by_label(&entry).is_some(), "the comp's layers are listed ({entry})");
+    let steps = h.state().session.history.undo.len();
+    h.get_by_label(&entry).click();
+    h.run_steps(3);
+    assert_eq!(layer_value(&h, base, prop), Some(map), "the parameter holds the layer id");
+    assert_eq!(h.state().session.history.undo.len(), steps + 1, "one undo step");
+    // The row names the picked layer, as the Timeline's Source row does.
+    assert!(painted_in(&h, rect_of(&h, &value_id), &entry), "the parameter row shows the layer's name");
+    h.state_mut().session.execute("edit.undo", json!({})).unwrap();
+    h.run_steps(2);
+    assert_eq!(layer_value(&h, base, prop), None, "undo restores None");
+
+    none_pick_clears(&mut h, &value_id, "なし", base, prop, map);
+}
+
+/// The visual record (the `ui_3d` ignored-snapshot convention): the Source drop-down open over
+/// the layer list, and the row after a layer is chosen. Renders with wgpu when `EC_SNAPSHOT_DIR`
+/// is set: `EC_SNAPSHOT_DIR=shots cargo test -p effectcraft-ui-egui --test ui_layer_source_picker -- --ignored`.
+#[test]
+#[ignore = "renders with wgpu; run with --ignored (set EC_SNAPSHOT_DIR to keep PNGs)"]
+fn snapshot_source_dropdown_open_and_chosen() {
+    let mut s = Session::default();
+    s.execute("comp.new", json!({"name": "Main", "width": 1280, "height": 720, "frameRate": 30, "duration": 5})).unwrap();
+    s.execute("comp.settings", json!({"renderer": "advanced3D"})).unwrap();
+    let sky = s.execute("layer.newSolid", json!({"name": "Sky HDRI", "color": "#66aaff"})).unwrap()["layer"].as_u64().unwrap();
+    let light = s.execute("layer.newLight", json!({"kind": "Environment", "name": "Env Light"})).unwrap()["layer"].as_u64().unwrap();
+    let (group, source) = {
+        let comp = s.active_comp().unwrap();
+        let opts = comp.layer(LayerId(light)).unwrap().props.sub("lightOptions").unwrap();
+        (opts.uid, opts.get("source").unwrap().uid)
+    };
+    let mut app = EffectcraftApp::new(s);
+    app.ui.timeline.open_layers.insert(light);
+    app.ui.timeline.open_groups.insert(group);
+    let mut h = Harness::builder().with_size(vec2(1600.0, 1000.0)).with_pixels_per_point(2.0).wgpu().build_eframe(|_| app);
+    h.run_steps(4);
+    let save = |h: &mut Harness<'_, EffectcraftApp>, name: &str| {
+        if let Ok(dir) = std::env::var("EC_SNAPSHOT_DIR") {
+            h.render().expect("render").save(format!("{dir}/{name}")).expect("save");
+        }
+    };
+    save(&mut h, "source_unset.png");
+    let at = rect_of(&h, &format!("timeline.prop.{source}.value")).center();
+    click(&mut h, at);
+    save(&mut h, "source_dropdown_open.png");
+    let entry = entry_for(&h, sky);
+    h.get_by_label(&entry).click();
+    h.run_steps(3);
+    assert_eq!(layer_value(&h, light, source), Some(sky));
+    save(&mut h, "source_chosen.png");
+}