Rules of light and shade in essence can be limited to three points:
1. Determining the location of the light source relative to the format.
While getting to the painting, its needed to determine the location of the source (or sources) of light in relation to the format. It can be within the format, covered by the object (backlight) or with a visible light source. Often the place of the light source is outside the format: for example, at the top center, right side, left bottom, etc. It should be remembered, that all parts of the composition are illuminated from the same source.
2. Determination of light intensity.
The intensity of illumination depends on the power of the light source, as well as on its distance from the object. A light source of even low power, located close to the object, creates a high contrast illumination, which, however, rapidly decreases with distance. A powerful light source (for example, the sun), even when away, provides uniform illumination throughout the format.
3. Rules for the distribution of light on the object and on the background.
0 - Highlight - the lightest white color, which allows the available white paint or paper color. Occurs only on shiny surfaces.
1 - Light - the most illuminated place on the object, the plane of the object is in relation to the light source at a right angle.
2 - Penumbra - is the plane of the object at any indirect angle relative to the light source.
3 - Reflex - the light reflected from the background or an adjacent object, occurs only if the background or a neighboring object is sufficiently bright.
4 - Shadow - a plane on the object located on the opposite side of the most illuminated place.
5 - Dropping shadow - a shadow in the background or an adjacent object that has contact with the object. A shadow will never be darker than a dropping shadow. A Shadow will never be darker than a dropping shadow.