More abstractly what you’re doing with the resistor is creating a very crude linear regulator, which is fine for most applications and if you’re careful about keeping your source voltage close-ish to the forward voltage of the LED this method can be fairly efficient.

Using an active constant current supply (as an example or many dedicated LED driver ICs do something very similar) can be marginally better as it allows you to reduce the waste from the linear regulator.

However, if efficiency is what you really care about you’ll need to go with a switching regulator. Here’s an app note going over the basics of that approach. and again you can usually find dedicated ICs for that approach.

Overall I’d recommend doing a detailed power budget and really seeing whether it’s worth the cost/trouble of implementing that because while you are correct it is usually more energy efficient it can be significantly less labor/material/maintenance/longevity efficient (hence the prevalence of the humble resistor…)