Photography is always about light! Light can be natural from stars (sun included here), or man made (fire included here). The source does not matter to either film or sensor. That said, understanding how different sources of light affect your camera’s ability to render an image is crucial to creating a good photograph.
The main property of light that is sensed by the camera is the color temperature. Color temperature determines the White Balance (the color your camera will define as white) and the associated adjustment of all other colors. The lower number color temperatures produce a warmer white (yellowish) in your image and the higher numbers tend to be colder (bluish). This used to be determined by film selection and ISO, but in digital cameras it often is an adjustment you can make for yourself (sometimes within post processing). Warmly lit images work very well with most portraiture, and the colder images work better in industrialized settings.
Landscapes and Portraiture tend to work best with warm light. This is often because the long shadows in a landscape create less contrast and since they occur during sunrise and sunset when our eyes (which have a limited dynamic range between the darkest dark and lightest light) can enjoy more of the image. The people that win awards with their landscape images shoot when the light is most dramatic. They tend to be active before sunrise, rest in the shae shade after 09:00 and resume their shooting after 17:00 (times are 9 AM and 5 PM respectively).
When photographing people, most photographers prefer warm skin tones as the subject will appear to be healthier looking. We tend to look almost dead when the light is creating a bluish cast. When you are trying to use natural light to make your portrait, the hour after sunrise and the hour before sunset create the most magical light for your subject. If shooting in the studio, you can either utilize gels on your lights to create that effect, or shoot the image at a camera white balance that is lower than normal color temperature of your lights and process the image at a higher one.
Light is the key to great images.