Realistic Outdoor Lighting in Unity HDRP

Unity has provided a handy cheatsheet for getting scientifically based lighting values into your scene, which can be viewed in the documentation on Physical Light Units:

https://docs.unity3d.com/Packages/com.unity.render-pipelines.high-definition@11.0/manual/Physical-Light-Units.html

For quick lighting setups outside, you will mainly be looking at the Color Temperature, Directional Light Intensities and Exposure Value rows.

Color Temperature and Directional Light Intensities can be found in the Directional Light component:

And the Exposure Value is found as a component added to a Volume, for instance the Sky And Fog Volume:

Example lighting with the cheatsheet

Let's have a play with these values to match the time of day we are after. Let's start at noon. With our reference sheet, the values we are concerned with are highlighted below:

With these values, our directional light settings look like:

And our exposure:

Have a play around with the different types of Exposure (i.e. Automatic Histogram, Automatic, Fixed, etc) and the compensation value to tweak the brightness of the final image. 

With those settings changed, we can get a nice day time lighting, when the directional light is set at 90 degrees on the X component of rotation:

With a similar to approach but for a 'low sun', where the directional light is set at 7 degrees on the X omponent of rotation:

And a moonlit scene: