Emitter group> Light Emitter parameter

Emitter group> Particles/sec modifier

This control lets you emit particles from lights. The Emitter Type Light(s) must be selected to activate this setting.

The advantages to using Light Emitters rather than the built-in emitter is that lights in After Effects are true 3D objects. This means their 3D motion path can be conveniently edited, and many lights can be used to create multiple emitters at once. See our tutorial for 'Emitting Particles from Lights' at the bottom of this page.

The Light(s) option in Emitter Type and its related Particles/sec modifier.

Particles/sec [Particles per second] Modifier

When Light(s) is active in the Emitter Type pop-up, the Particles/sec Modifier can tell the Light Emitter to emit different amounts of particles by using properties of the After Effects Light. Essentially, the Particles/sec Modifier is altering the value defined in Particles/sec in the Emitter group.

Particles/sec Modifier has four options. Each choice takes its modifier from a different Light property, which is located in the Light's layer properties in the Timeline. For example, if you set the pop-up to Light Intensity and the emitter's Light Intensity value is set to 90%, then the Particle/sec value will be 90% of the set value in the plug-in. In other words, a value of 100 particles/sec would become 90 particles/sec. These controls are useful because they can tie a particle emission rate to the light's behavior. For example, a flickering light created by random keyframes for the Light Intensity can cause the emission to appear to pulse with the light. Often, if the light is not casting shadows (since it just being used to emit particles), the Shadow Darkness and Diffusion are unused in the scene and can be set up with keyframes or expressions to create more complicated emitter behaviors.

- Light Intensity will use the Intensity value to change the emission rate.
- Shadow Darkness will use the Shadow Darkness value to change the emission rate.
- Shadow Diffusion will use the Shadow Diffusion value to change the emission rate.
- None does not change the emission rate based on any of the Light's properties. Useful when light intensity is used for other things (such as actually lighting a scene).

The Light's layer properties that can be modified.

Options Panel> Light Emitter Name

The Light Emitter is linked to the Light Emitter feature in the Options panel. When a comp Light has the same name as the Options Light Emitter name, that Light will be used to control the particle emission.

Enter a Light Name in the Name field, and use that same name for the Light layer in your Timeline. This will link that Light Emitter to that specific Light.

By default, this Light Name is named 'Emitter,' and that is often an easy standard to use. But the Light Name can be changed to anything as long as the Light's layer name matches. More info on the Options Panel page.

Particular displays a reminder to name the Light Emitters correctly.

At Left, the Light Emitter Name field in Options Panel. At right, the Light layer uses the same naming convention.

Technical Notes

- When emitting particles from Lights, the particle color comes from the Light's Color layer property. This coloration can be changed with the Color over Life gradient in the Particle group> Set Color control.
- When Light Emitters are keyframed and the keyframes are edited extensively, cache inconsistencies can occur. These will manifest as jerkiness in the animation (the Emitter jumps from one frame to the next). To get rid of the erroneous frames from the cache, use Edit>Purge>Image Caches and re-render.

Tutorial: Emitting Particles from Lights

Start with a new comp (Ctrl/Cmd-N), make it 640x480 at 30 frames per second for 5 seconds.

Create a Spot Light (Layer>New>Light). Name it 'Emitter1' and make it red.

Create a comp-sized Solid (Ctrl/Cmd-Y), choose Make Comp Size, then click OK.

Apply Effect>Trapcode>Particular to the solid. In Particular, set Emitter>Emitter Type to Light. Set Emitter>Direction to Directional.

Now go forward in time to 1:00 (one sec). The comp window looks like this:

X Rotation = 0 | X Rotation = -120

Particles are emanating from the light. Now bring up the Rotation properties for the light by selecting the layer in the Timeline and hitting 'R'. Try scrubbing the X Rotation back and forth a bit and notice how the particle beam corresponds to the light's orientation.
Open Options for the Light and edit Cone Angle. Notice that the width of the particle beam depends on Cone Angle for the light.
You will notice that particles are born in a volume around the light rather than at the exact point of the light. This is because the Emitter Size is non-zero by default. Try changing the Emitter>Emitter Size value to 0.

Now hit RAM preview:

Adding a second Emitter to the scene

Go to Time 0:00 (zero) and create a new Spot Light. Name it 'Emitter2' and make it blue. Open its layer properties. Set position to (170,270,-200). Set X Rotation to -40 and Y Rotation to 120.

Hit RAM preview:

Have fun with the Light Emitters! And remember:
When the Light Emitters are keyframed and the keyframes are edited extensively, cache inconsistencies can occur. These will manifest as jerkiness in the animation (the Emitter jumps from one frame to the next). To get rid of the erroneous frames from the cache, use Edit>Purge>Image Caches and re-render.