Improve Bloom 3D lighting (bevyengine#11981)

# Objective

- With the recent lighting changes, the default configuration in the
`bloom_3d` example is less clear what bloom actually does
- See [this
screenshot](https://github.com/bevyengine/bevy-website/pull/1023/files/4fdb1455d5a3371d69db32b036e38731342b48de#r1494648414)
for a comparison.
- `bloom_3d` additionally uses a for-loop to spawn the spheres, which
can be turned into `commands::spawn_batch` call.
- The text is black, which is difficult to see on the gray background.

## Solution

- Increase emmisive values of materials.
- Set text to white.

## Showcase

Before:

<img width="1392" alt="before"
src="https://github.com/bevyengine/bevy/assets/59022059/757057ad-ed9f-4eed-b135-8e2032fcdeb5">

After:

<img width="1392" alt="image"
src="https://github.com/bevyengine/bevy/assets/59022059/3f9dc7a8-94b2-44b9-8ac3-deef1905221b">

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>

crates/bevy_core_pipeline/src/bloom/settings.rs

@@ -106,6 +106,8 @@ pub struct BloomSettings {
 
 impl BloomSettings {
     /// The default bloom preset.
+    ///
+    /// This uses the [`EnergyConserving`](BloomCompositeMode::EnergyConserving) composite mode.
     pub const NATURAL: Self = Self {
         intensity: 0.15,
         low_frequency_boost: 0.7,

examples/3d/bloom_3d.rs

@@ -36,19 +36,20 @@ fn setup_scene(
             transform: Transform::from_xyz(-2.0, 2.5, 5.0).looking_at(Vec3::ZERO, Vec3::Y),
             ..default()
         },
-        BloomSettings::default(), // 3. Enable bloom for the camera
+        // 3. Enable bloom for the camera
+        BloomSettings::NATURAL,
     ));
 
     let material_emissive1 = materials.add(StandardMaterial {
-        emissive: Color::linear_rgb(2300.0, 900.0, 300.0), // 4. Put something bright in a dark environment to see the effect
+        emissive: Color::linear_rgb(23000.0, 9000.0, 3000.0), // 4. Put something bright in a dark environment to see the effect
         ..default()
     });
     let material_emissive2 = materials.add(StandardMaterial {
-        emissive: Color::linear_rgb(300.0, 2300.0, 900.0),
+        emissive: Color::linear_rgb(3000.0, 23000.0, 9000.0),
         ..default()
     });
     let material_emissive3 = materials.add(StandardMaterial {
-        emissive: Color::linear_rgb(900.0, 300.0, 2300.0),
+        emissive: Color::linear_rgb(9000.0, 3000.0, 23000.0),
         ..default()
     });
     let material_non_emissive = materials.add(StandardMaterial {
@@ -60,6 +61,8 @@ fn setup_scene(
 
     for x in -5..5 {
         for z in -5..5 {
+            // This generates a pseudo-random integer between `[0, 6)`, but deterministically so
+            // the same spheres are always the same colors.
             let mut hasher = DefaultHasher::new();
             (x, z).hash(&mut hasher);
             let rand = (hasher.finish() - 2) % 6;
@@ -90,7 +93,7 @@ fn setup_scene(
             "",
             TextStyle {
                 font_size: 20.0,
-                color: Color::BLACK,
+                color: Color::WHITE,
                 ..default()
             },
         )
@@ -219,7 +222,7 @@ fn update_bloom_settings(
             *text = "Bloom: Off (Toggle: Space)".to_string();
 
             if keycode.just_pressed(KeyCode::Space) {
-                commands.entity(entity).insert(BloomSettings::default());
+                commands.entity(entity).insert(BloomSettings::NATURAL);
             }
         }
     }