TPE 3D offers three different lighting mode, each with a different intended purpose: Navigation, Natural and Artificial Highlights.
We'll talk about Natural Lighting first, as that is the default mode when you start the app. Natural Lighting means that the 3D scene is lit using a simulation of the natural lighting you would experience at that time and place (assuming a cloudless sky).
When you change the date or time, the lighting changes accordingly. This is the mode you'll most likely use 95% of the time. You only need the other modes in specific circumstances - more on that below.
When Navigation Lighting is enabled (using the lightbulb at the lower left of the screen), the directional lighting of the sun and moon is disabled and bright, neutral coloured ambient lighting is enabled instead.
It's rather like when the curtain comes down on a theatre show and the backstage working lights are turned on: you do it because you have a task to complete quickly and efficiently - in this case, navigating the 3D scene to get the camera where you need it.
In many places that photographers frequent, e.g. Iceland, northern Norway, Alaska, the natural lighting can be relatively dim, even during daylight. And at night, the natural lighting of the landscape is of course dark.
Switch Navigation lighting on to help position the camera quickly. When you're finished, just move the timeline, or tap the lighting mode button once again and Natural Lighting will be restored.
Artificial Highlights changes the colour of the Sun and Moon lighting from their simulated "natural" colour temperature to a bright artificial colour: red for the sun and blue for the moon.
This mode can be useful to make sure you are correctly interpreting the lighting in the scene, for example, to distinguish between a naturally brighter area of the map vs something that is actually being lit by the sun or moon.
Moonlight in particular can be tricky to distinguish. Enabling Artificial Highlights can be helpful in these circumstances. Compare, for example, the following two screenshots - it's quite clear what is lit directly by the moon when Artificial Highlights are enabled:
Note: this feature is also slightly forward looking. We hope to offer satellite maps at some point in the future. Usually satellite map imagery has some shadows "baked in" based on the timing of the photograph and attitude of the satellite's camera towards the Earth. When there are shadows arising from both the source imagery and the simulated lighting, it can be tricky to distinguish which is which. We hope to use the Artificial highlights feature to make that an easier task.