LOD

Level of Detail renders distant instances using progressively simpler geometries.
Each LOD level is a separate InstancedMesh2, so each level costs one draw call.

const iMesh = new InstancedMesh2(new SphereGeometry(5, 30, 15), mat, { capacity: 100000 });

iMesh.addLOD(new SphereGeometry(5, 20, 10), mat, 100);
iMesh.addLOD(new SphereGeometry(5, 10, 5), mat, 200);
iMesh.addLOD(new SphereGeometry(5, 5, 3), mat, 300);

Metric

The metric is the distance from the camera by default, and metrics must increase.
Set useDistanceForLOD to false to use the screen size instead, with decreasing metrics:

const iMesh = new InstancedMesh2(geo, mat, { useDistanceForLOD: false });

iMesh.addLOD(geometryMid, mat, 0.1);
iMesh.addLOD(geometryLow, mat, 0.02);

An optional hysteresis (between 0 and 1) prevents flickering when an instance is close to a threshold:

iMesh.addLOD(geometryMid, mat, 100, 0.1);

First LOD

The first LOD (index 0) is the mesh itself and doesn’t need to be added. Its metric defaults to 0 when distance-based or Infinity when screen-size based.
Change it with setFirstLODMetric before addLOD: it’s useful when the parent mesh is not the most detailed one, so a more detailed level is used near the camera.

iMesh.setFirstLODMetric(50);

Update and Remove

iMesh.updateLOD(1, 150);         // change the metric of a level
iMesh.updateAllLOD([100, 200]);  // change all metrics
iMesh.removeLOD(2);              // remove a level