Turned off all my objects in the blend and viewport is still slow!

How visible are those candelabras? Could you replace them with a lower res version?

  1. Is “instancing” new (2.8.+) ?

  2. If I use it to make a candelabra like above, (let’s say 40 copies of a light in a circle), and I’m ready to render it…, do I leave things as they are, or should I combine the 40 copies into one object in some way?

No, instancing is not new. We used to be able to instance groups. Now that they’re called collections, we can instance collections. We can instance stuff with geonodes as well now, in a more flexible way. However if all you need is hand-place a candelabra in a few parts of your scene, then creating collection instances is very straightforward. You don’t need to combine anything, all you need is that everything is into one collection.

But… could you combine them?

In other words, is there a menu item or button to “combine/apply/join” instances, so that 40 instances become 1 BIG instance ?

One point of having collections instances is that you don’t have to join objects together, but you can always do so, yes. I mean, you can join meshes, but not lights. What are you trying to do ?

…learn about instancing. Thanks for your help.

Oh I thought you were trying to achieve something in particular your question being so precise. What you CAN do is fill up a collection with collection instances (referencing another collection obviously) and instance that collection.