Nature almost never gives you perfect light, and the time to paint it! Very often you must make up the light, or intensify it when it dims. When that happens, use the tool of planar values to capture the light.
Planar values is the concept of light falling on the same plane. In this illustration, you see the rounded shape of a head, notice how the parts that face the light are lighter, the parts that curve away from the light are darker. Part of light logic is knowing how light will wrap around a shape.
The same concept applies to the landscape. Everything that is facing the light will be illuminated, things facing away from the light will be in shadow. Here's the subject and the lighting:
The time of day is about 9am and the light is low on the Eastern horizon, you can see the sun reflected in the water so that gives you an idea of the planes the light is hitting. Notice the grass in the foreground is illuminated, the shoreline is illuminated and shadows are cast forward on the banks on both sides of the pond.
Here's my value sketch of the same scene:
You get the idea of the light and shadows of this scene. Here's a color study of the same scene to see more of the light:
now, if I wanted to change the light in this scene to a sunset scene instead, I would need to change the planar values. The sun would be low on the horizon, the treeline would be darker and in shadow, the light would rake across the palm in the foreground which would be much darker. The landscape would darken and be in low key. The sky would be warmer.
If I wanted to change the light to noon, then the planar values would be totally different. The light would be right overhead, and there would be strong cast shadows under the trees, and intense highlights on the palm in front. Things behind the tree would be lighter and cooler, things next to the tree would be warmer and darker. Like this:
Understanding planar values helps you to play with lighting in your paintings. It gets easier the more you do it and the more you paint and study light on the landscape. Even when I'm not painting, I'm painting with my eyes! I study the landscape and the light. I marvel at cast shadows and highlights. Here's my finished piece from the scene:
Its not perfect, but its my version. Hope this helps you and your painting and I always love when readers post thier versions. Thanks for reading and subscribing!