Working on a 250' x 250' warehouse/production facility. 150' x 240' is 18' high rack storage, 100' x 150' production area, 50' x 90' office, and 50' x 90' misc. Lighting is LED at ~20' AFF. Production and misc. areas are dimmable. The office is mostly dimmable. At the moment the office lights are 120V and the rest is 277V, but the office can be 277V if needed. There is a single 277V lighting panelboard.
I can't in good conscience put in battery packs because of the battery maintenance issues. But going to an emergency generator requires lots of dedicated conduits which are costly and potentially dedicated fixtures. But, even with that it should (?) be the least long term cost. And with dimmable fixtures, it will be interesting how (if) to use any of them for the egress lighting.
What is the "preferred" method(s) to providing emergency lighting for large areas?