Thanks Suthriel. That tutorial video you linked to is a good source of information about how I can use light functions to create the effect I’m going for. So big thanks for that!
BUT unfortunately his technique is a hack that involves creating three lights (red, green, blue) where you’d normally need one to get around the fact that light functions can’t handle colour. So that’s a 3x performance hit, which for ray tracing area lights is a big deal.
You mention that Porsche used a Media Player as a texture (not a light function). But when I do that my nice soft area light just turns into a movie projector. This problem is demonstrated very clearly in your own result video. Your rectangle light is somehow magically projecting a perfectly legible image of peoples faces etc onto the floor - like a projector. A real TV screen has no lens in front of it, and therefore it just makes a soft blob of coloured light (which the tutorial creates with blur filters, light functions, 3x the needed number of lights etc). I’m lighting my scene with multiple giant video walls, so the difference is huge.
I don’t want to be dismissive of your very helpful answer - you have given me a way forward! But I’m still wondering if the Porsche guys were doing something a little less “hacky” than creating source texture cameras to film their screen, duplicating the light 3 times, etc.