Important information about tourism in Costa Rica - Florida

For sunbeams to appear in a forest, you need 1) a high, dense canopy punctured by a few openings, 2) air filled with dust, vapor, or smoke, and 3) an angle of view toward the sun.

Sunbeams influence pick out random elements of the scene to spotlight, and they lighten the values of everything beyond them.

Using traditional oil paint, this can be accomplished by scumbling a light, semi-opaque shape over the dry background where the beams appear. However, white pigment will reduce the chroma and make it chalky, so the color may need to be restored by glazing.

Alternately the colors can be achieved by careful premixing. In this painting, I premixed one string of colors for the areas inside the sunbeam, and a whole separate string for the colors of the darker unlit forest.
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Previous post on Scumbling

The painting is from Dinotopia: The World Beneath, and you can get copies at my website.

There's more on atmospheric effects in my book Color and Light: A Guide for the Realist Painter.