As the sphere turns away from the light it becomes darker in value and less intense (less chromatic) in color. The hue (property of color pertaining to the spectrum of colors, whether blue, yellow or in this example, orange) remains the same for the entire sphere. The hue of a form can be determined by a form's local color.
Local color is the inherent color of a form under the specific lighting scenario. A form's local color can be identified at the point where a form is most facing the light. As the form turns away from the light, less of the local color is diffusely reflected and the form becomes darker in value and less intense (less chromatic) in color. The reason for this phenomenon is based on a form's orientation to the light source(s).
Light's Interaction With Form
Many light rays are projected from the light source in every direction. The image on the left only shows a small number of the millions of light rays emitted from a light source. (Please note, these diagrams are simplified for illustration purposes only).
Each of these light rays is made up photons. A photon is essentially a microscopic piece of light. Photon's are made up of wavelengths from the color spectrum (consisting of colors ranging from red, orange, yellow, green, blue and violet). The quantity of the wavelengths from photons projected from an object causes the combined wavelengths of photons to appear as a specific color. Photons are made up of the same color properties of the light source and their combined make up is very influenced by any form that it interacts with.
(Doug Flynt has published a very informative article on the reflection of colored light on his blog here).
The photon originally was composed of wavelengths that when combined with the wavelengths of the millions of other photons emitted from the light source appeared as white as the light source. Once projected from the light source, the photon traveled in its light ray to meet the orange sphere. Due to diffuse reflection, once the group of photons emitted from the light source interact with the sphere some of the photons and their wavelengths are absorbed by the sphere while some photons and their wavelengths are reflected. This interaction causes the wavelengths of the reflected photons to combine and reflect the color properties of the sphere. (Scott Waddell has also created a very informative video on the science of light that can be viewed here). Photons continue along their path to enter a viewer's eye and make up the images that one sees.
There are millions of light rays that strike a form. The diagram above shows, in a constricted sense, the distribution of light if six light rays were projected from a light source. The more a plane is facing the light the more light rays can reflect off its surface area.
In this example, because plane A is most facing the light it receives 3 light rays, plane B receives 2 light rays and plane C only receives 1 light ray to reflect. Therefore the less light that is received by a plane the less light rays can reflect the color of planes. And as the planes turn away from the light they become darker in value and less intense in color.
The interaction between light and form creates specific gradations that are essential to conveying the structure of form. Although much of this post discussed color, drawing has a critical role in representing these gradations. No matter the color of a form, representing the structure of form is entirely dependent upon the drawing of the shapes of form and its gradations in value.
-Fate of Photons. (n.d.). Retrieved December 27, 2014, from http://www.newton.dep.anl.gov/askasci/phy05/phy05213.htm
The type of analysis into gradations that I have presented in this post may seem to be over complicated. So I would like to include a statement describing why these types of investigations into the appearance of form have been important to my artistic development.
It is my understanding that the representational art that I am pursuing to make has much less to do with any "skill" as it has to do with awareness and acceptance of what one sees (both optically and conceptually).
For example, once one accepts that the images they see are composed of shapes one can draw the subtleties that one is aware of in those shapes. Once one accepts that form is turning more or less towards the light one can represent the turning of form that one is aware of. This theory even extends to material handling. Once one accepts that the gradations in their piece represent sculptural volume and that their tool of a pencil or brush is a chisel, one becomes aware of how to apply their chisel to affect their sculptural piece in an intended way.
In my opinion, the most important ability that I am striving to develop in my representational pursuits is the discipline to become and remain aware of what is occurring without interruption in my thought process. The most beneficial aid that I have found in this pursuit is acquiring more information on the science of light on form, because nature holds no secrets. By enhancing my understanding of what is percieved I may heighten my awareness to more fully represent what is seen.