Energy usage of LEDs (always lighting and dimming vs always on)
LEDs themselves essentially have no "memory" whatsoever, and on the scale of seconds the same is most likely true for the driving circuitry. That is, the most efficient usage is to use exactly as little light as you need at any moment.

There is a slight effect where LEDs become less efficient when hotter. Therefore, dimmer is more efficient than brighter, since there is less heat being produced. The batteries storing energy from your solar panels (I assume you have some) will also be more efficient at lower overall power.

In some other lighting systems, dimmers waste energy. This is not true for LED lighting with built-in dimming — the power supply is controlling the average current through the LEDs all the time, and dimming is just changing the target current.

In summary: to optimize for run time, turn off or dim lights as much as you can reasonably manage. There is no reason to leave on, or bright, a light you don't need.