This is the 2007 version. Click here for the 2017 chapter 04 table of contents.

Light and the Visual Waveform

Light is a form of electromagnetic radiation. It is the same type of energy as television waves and radio waves. As the diagram shows, visible light corresponds to a small segment of the electromagnetic spectrum.

Visible light is a form of electromagnetic radiation, similar to X-Rays, radio, and television signals

What type of energy is light? What is the relationship of wavelength to frequency?

The frequency of light refers to the number of cycles in the electromagnetic radiation per second. These cycles are fluctuations in the strength of the radiation. Wavelength is the distance from one cycle to the corresponding part of the next cycle.

What does Roy G. Biv stand for?

The visible spectrum is the band of electromagnetic radiation we can see: the part we call light. The visible spectrum contains all the colors of the rainbow, from red to violet. The colors of the rainbow can be memorized in order by remembering the name Roy G. Biv. This stands for red, orange, yellow, green, blue, indigo and violet. Indigo is hard to see as a distinct color. Indigo probably would not be in the list except for the fact that Isaac Newton, who proposed this classification, liked the number seven.

How is frequency related to wavelength?

The colors of the spectrum are called hues. Going from red to violet through Roy G. Biv, each color represents a slightly higher frequency, therefore a shorter wavelength. With shorter wavelength, more cycles fit into a second. Blue has the highest frequency and the shortest wavelength in the visual spectrum.

Wavelength and amplitude

How is amplitude related to luminance and brightness?

On a graph, the amount of energy in light is shown by the height of the wave: its amplitude or strength. A 100 watt light gives off more energy than a 50 watt light. Changes in amplitude of light lead to greater amounts of reflected or transmitted light called luminance, the amount of illumination. Other things being equal, increased luminance results in the psychological experience of increased brightness.

What is saturation?

Light is hardly ever pure. It usually contains a mixture of different frequencies. When you see the color red, it is typically a complex mixture of different wavelengths with red frequencies dominating. Light containing only one frequency is said to be completely saturated. Completely saturated colors do not occur in nature, although the colors of a rainbow come close. Highly saturated colors look intense, while unsaturated colors look dull and gray.

To summarize, there are three main properties of the visual waveform that correspond to psychological experiences: frequency of the wave (that influences our perception of hue), amplitude of the wave (that influences luminance and thus our experience of brightness), and saturation of the wave (that corresponds to purity or complexity of the color).

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Copyright © 2007-2011 Russ Dewey