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 ā€œinstancingā€ new (2.8.+) ?

  2. If I use it to make a candelabra like above, (letā€™s say 40 copies of a light in a circle), and Iā€™m ready to render itā€¦, 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 theyā€™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 donā€™t need to combine anything, all you need is that everything is into one collection.

Butā€¦ could you combine them?

In other words, is there a menu item or button to ā€œcombine/apply/joinā€ instances, so that 40 instances become 1 BIG instance ?

One point of having collections instances is that you donā€™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 ?

ā€¦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.