LED manufacture has a multi-continental supply chain, which may not always be there when we need it.
Candles and oil lamps have truly rubbish efficiency, but store well and can be DIYed.
Incandescent has much better (but still lousy) efficiency with a short supply chain and widely proliferated tech.
Gas discharge and microwave-sulphur-plasma can almost compete with LED on efficiency, and with incandescent on supply chain length. But don't scale very small.
Cathodoluminescence, now that I need to experiment with :p