Fundamentals of Color

Colored light is radiated when electrons in molecules move from a higher energy level to a lower one. If some of this radiated energy falls within the visible wavelength range it is detected by the human eye.

• Visible light is a small part of the electomagnetic spectrum, which includes X-rays, ultraviolet (UV), microwaves, Infrared (IR), radar and radio waves. (See figure below.)

• Visible light lies in the 400 and 700 nm range of wavelengths.

• X-rays and UV have shorter wavelengths and microwave, IR, radar and radio waves have longer wavelengths than visible light.

• Some mammals can perceive into the IR and UV range.

• Light can treated as both an energy carrying particle called a photon and as a wave. Its wavelength determines the perception of hue, while its particle behavior determines the way it causes light sensitive media such as photographic emulsions and photopolymers undergo chemical and physical changes.

White light - Composed of many colors, essentially all of the colors in the visible range with equal intensities of each wavelength.

• Isaac Newton showed that white light could be split into all colors of the rainbow by passing through a prism.

• Visible light appears to be split up into three predominant bands of light, red, green and blue.

• This results from how the human eye perceives light in terms of red, green and blue.

• Thus, these are called the primary colors of light.

• Balanced amounts of R, G and B produce white light.

• Computer monitors and TV screens use RGB to display color. (Because both employ Cathode Ray Tubes, i.e.CRTs.)

Spectral Reflectance Curves - Plot of amount of reflected light versus wavelength. The spectral reflectance of a give colored surface gives a unique “fingerprint” of the color of the surface.

• The perceived color dependson how the relative amounts of different wavelengths in the spectralreflectance curve. A predominately green spectral reflectance curve isshown in Figure 2-4 of the book.