2. Rate, Duration and Lifetime¶

Separate how often particles are born from how long each particle survives.

Continue from the first lesson¶

Open lesson 1 and save a copy as 02-emission-timing.blend. Keep the source, velocity, Radius, 24 fps, and Substeps 4.

Shorten particle life¶

Change the Emitter Lifetime from 96 to 48 frames. Keep lifetime Variation at 0.
Keep Rate 120 /f, Start Frame 1, and Duration 96.
Replay from frame 1 to 72.

At 24 fps, 48 frames is two seconds. Emission continues through frame 96, but each particle dies after its own two-second life. The stream reaches a stable length.

Control	What it changes
Rate	Births per frame or per second
Start Frame	When emission starts
Duration	How long rate-based emission remains active
Lifetime	How long each individual particle survives
Radius	Size and contact radius, not birth count

A steady blue particle stream limited by its lifetime — Frame 72: the stream keeps a stable length while births replace dying particles.

Births and deaths balance¶

Compare frames 24, 48, and 72. The population grows first, then stays near 120 × 48 = 5760 while births replace deaths. A boundary frame can differ by one emission batch.

Density uses Rate. Volume Grid and Hexagonal fill once on Start Frame and use Particle Spacing; changing Rate does not change those packed fills.

Optional: stop emission early¶

Set Duration to 24 and replay to 72. The source stops after a short burst and the remaining particles eventually die. Restore Duration 96.

The same rate can be expressed as 2880 /s at 24 fps. Per-second Rate preserves births per second when fps changes; Duration and Lifetime stay in frames. Keep 120 /f for the following lessons.

Troubleshooting¶

The stream never clears: check both Lifetime and Duration.
Changing Rate has no effect: check for Grid or Hexagonal fill.

Reference: Emitter timing.

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