Light is a thing that cannot be reproduced, but must be represented by something else – by color. -Paul Cezanne.
My academic art studies in Finland consisted of regular model drawing. We drew with coal on big paper. I loved it. The model drawing was our method or means of learning the basics of art: composition, perspective, textures, volume, and light. We learned well by doing and the critic from our teacher and from each other. The theory was mostly in the practice.
Painting was another thing. Well, I loved it too, but the approach was different. Painting was about color, surface, texture. We chose what we would work on. At one point I painted with a roller, 5 x 2 meters big. I have been later thinking how it was self-evident for most of us to forget the light. I read a quote(whose, I can't remember), that 'light was an emperor that died in painting in the beginning of the 20th century'. I'm not going to recapitulate the late art history here, but it did seem so. The division was almost that painting was all about surface, and when light entered the picture(!), it was illustration. This is a exaggeration, of course.
Since post-modernism, everything has been possible and there is many an artist who paint 'light'. I have thought about this while drawing my next graphic novel. In comics the line art and so called 'flats' make the illustration. Often minimum shades are included. There are no rules though, and there are comic artists who have played with this. I enjoy drawing varied perspectives, angles, and all the rest. When it comes to light and shades, it's almost like an art theory class in my head: So, light comes from here... and light is from the sun, thus the color should be...' . Sometimes it is great to experiment and stretch the limits of 'natural world' and at the same time so that the picture makes sense as a part of the story - your trees can't be red. Or at least not throughout the book, and not MY trees.
Here a watercolor 12 x 12 cm called 'Nature'.