My wife and I intend to arrive in Lyon the day before the festival and stay to the end, before moving on to Switzerland by train. We are either flying in or coming by train, unsure as of yet. I know certain parts of town are difficult to get to the hotels at times due to security restrictions, but we want a hotel accessible to Old Town and the light installations, and not too far to walk. And a really nice hotel. Any advice? Thanks!
" ...we want a hotel accessible to Old Town and the light installations..."
You probably do, but I want to make sure: you realize those are two different things, don't you? Some years there is a display in Vieux Lyon (old Lyon) but most of them are in the presqu'île, usually one at the Basilique de Fourvière, and sometimes in Parc de la Tête d'Or.
I'm unfamiliar with "really nice" hotels in Lyon. We typically stay at good but not extravagant spots; most commonly Hôtel des Artistes and Hôtel des Célestines.
Maybe try the Intercontinental at Hôtel Dieu or the Sofitel near Place Bellecour. Both are probably 4 or 5 stars and in the presqu'île where most of the events associated with the fête are located.
Edited to add: I hope you like crowds. Some of the displays/events are magical and amazing, but the crowds are formidable.
Sure crowds are fine, last year we were at the Nice Festival, often go to this type of thing.
But will have difficultly accessing hotels in the presqu'ile due to security?
Those kinds of crowds make me want to be very, very far away.
That said, I understand some people don't mind them.
But wow. Not my cup of tea.
I go to music festivals all the time, when able. Crowds are sometimes an annoyance, for example outside a hotel room. But also add excitement and fun. Still, the rest of the trip--Montreux, Interlaken, and Bern, should be more low key. Yin and Yang.....
To get to one of your questions I did not address: no, I don't think you'll have any difficulty accessing your hotel for security reasons. I was living in Lyon when the attacks in Paris at Bataclan and elsewhere occurred and after the Nice attack on Promenade des Anglais.
In fact, I was the only one in my company's office the day after the Nice incident when I got a call from our regional manager and had to track down and check on all my co-workers. Fortunately, everyone was fine.
I don't think security will be any issue with respect to going to or from your hotel. Most of the security at Fête des Lumières relates to getting into and out of the events.