Electromagnetic Spectrum, Light Perception, and Visual Processing

Electromagnetic radiation spectrum

The electromagnetic spectrum is the complete range of all types of electromagnetic radiation, from very long radio waves to very short gamma rays, including visible light, infrared, ultraviolet, X-rays, and microwaves.

Wavelength (as related to light energy)

Wavelength is the distance between two consecutive peaks (or troughs) of a light wave; it determines the light's color.

Amplitude (as related to light energy)

Amplitude is the height of a light wave from its midpoint to its peak; it determines the brightness or intensity of the light.

Visible light

Visible light is the portion of the electromagnetic spectrum that human eyes can detect; it includes all the colors of the rainbow.

How visible light reaches the eyes

Light enters through the cornea, passes through the pupil, is focused by the lens onto the retina at the back of the eye, where specialized photoreceptor cells detect it.

Range of wavelengths visible to humans

The human eye detects light with wavelengths approximately between 380 and 750 nanometers (nm).

Sensation

The process by which sensory organs receive and detect physical energy (like light, sound, or touch) from the environment.

Perception

The process by which the brain organizes, interprets, and consciously experiences sensory information.

Features of visible light sensed by the eye

Wavelength, amplitude, and purity (mixture of wavelengths) are the main features detected by photoreceptors in the eye.

How wavelength is perceived by the visual system

Wavelength is perceived as color or hue.

How amplitude is perceived by the visual system

Amplitude (wave height) is perceived as brightness or intensity.

How purity of the light source is perceived by the visual system

Purity (whether light contains one wavelength or a mix) is perceived as saturation; pure light appears vivid, while mixed light appears washed-out or pale.

Color perceived at ~470 nm wavelength

Light with a wavelength around 470 nm is perceived as blue.

Color perceived at ~700 nm wavelength

Light with a wavelength around 700 nm is perceived as red.

Where light-sensing specialized cells are found

Specialized cells that sense light are found in the retina at the back of the eye.

Differences between rods and cones

Rods: very sensitive to light, work in dim light, detect black and white, found mostly in the periphery of the retina. Cones: require brighter light, detect color and fine detail, concentrated in the fovea.

Transduce (definition)

To transduce means to convert one form of energy into another — in vision, photoreceptors convert light energy into electrical signals for the brain.

What happens if a person is missing one type of cone receptor?

If one cone type is missing, the person has color vision deficiency (color blindness) and cannot distinguish some colors that normally require that cone's input.