26.3 Color and Color Vision
3 min read•june 18, 2024
Color perception is a fascinating aspect of human vision. Our eyes contain specialized cells called cones that detect different wavelengths of light. The brain interprets signals from these cones to create the vibrant world of color we experience.
Light sources play a crucial role in how we perceive colors. From warm bulbs to cool lights, each source affects color appearance differently. Understanding these differences helps us appreciate the complexity of color vision and its impact on our daily lives.
Color Perception and Vision
Color perception in human eyes
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- Human eye contains cells called
- Rods are sensitive to low light levels and provide (night vision)
- Cones are responsible for color vision and function best in bright light conditions, providing (daytime vision)
- Cones are divided into three types, each sensitive to a specific range of wavelengths
- (long-) are most sensitive to red light (around 560 nm)
- (medium-wavelength) are most sensitive to green light (around 530 nm)
- (short-wavelength) are most sensitive to blue light (around 420 nm)
- Brain interprets the relative activation of these three cone types to perceive different colors
- Equal stimulation of L-cones and M-cones with little S-cone stimulation is perceived as yellow
- Activation of L-cones alone is perceived as red, while activation of S-cones alone is perceived as blue
Properties of light sources
- Incandescent light bulbs emit a continuous of light, with more energy in the longer wavelengths (red and orange)
- Objects illuminated by incandescent light may appear warmer in color (candlelight)
- Fluorescent light bulbs emit discrete spectral lines, with peaks in the blue and green regions
- Objects under fluorescent light may appear cooler and less natural (office lighting)
- (LEDs) can be designed to emit light in specific wavelength ranges
- (CRI) measures how accurately a light source reproduces colors compared to natural sunlight
- High CRI LEDs (90+) can closely mimic sunlight and provide accurate color rendering
- Sunlight has a broad, continuous spectrum and is considered the reference for accurate color perception
- of sunlight varies throughout the day, affecting the perceived colors of objects (warm at sunrise/sunset, cooler at midday)
Theories of color vision
- ()
- Proposes that the human eye has three types of cone cells, each sensitive to a different range of wavelengths
- Explains color perception based on the relative activation of these three cone types
- Strengths:
- Accounts for color matching experiments and the ability to perceive a wide range of colors
- Explains as a deficiency in one or more cone types
- Limitation: Does not explain certain color vision phenomena, such as afterimages and color contrast effects
- ()
- Suggests that color perception is based on the opposing responses of three color opponent channels: red-green, blue-yellow, and black-white
- Proposes that colors are processed in an antagonistic manner, e.g., a color cannot be perceived as both red and green simultaneously
- Strengths:
- Explains afterimages, where staring at a color (red) produces the perception of its opposite (green) when looking away
- Accounts for color contrast effects, where the perceived color of an object is influenced by its surrounding colors
- Limitation: Does not directly address the existence of three cone types
- Modern understanding of color vision combines elements of both theories
- Trichromatic theory explains color perception at the receptor level (cones)
- Opponent process theory describes color processing at the neural level (ganglion cells and beyond)
- Together, they provide a comprehensive explanation of how humans perceive and process color information
Light and Color
- is a form of that humans can perceive
- The spectrum of ranges from about 380 to 700 nanometers in wavelength
- Different wavelengths of light correspond to different perceived colors
- occurs when different colored lights are combined, resulting in a brighter color
- happens when pigments or filters remove certain wavelengths from white light
- Color blindness is a condition where individuals have difficulty distinguishing between certain colors, often due to missing or defective cone types
Key Terms to Review (31)
Additive Color Mixing: Additive color mixing is the process of combining different wavelengths of light to create a new color. It is a fundamental concept in color theory and the understanding of how we perceive color in the world around us.
Color Blindness: Color blindness, also known as color vision deficiency, is a condition in which an individual has difficulty perceiving or distinguishing certain colors due to the abnormal functioning or absence of color-sensitive photoreceptor cells in the retina. This condition can affect an individual's ability to perceive and differentiate between various colors, which is an important aspect of color and color vision.
Color constancy: Color constancy is the feature of the human visual system that ensures perceived colors of objects remain relatively constant under varying illumination conditions. It allows us to recognize colors regardless of the lighting environment.
Color Rendering Index: The color rendering index (CRI) is a measure of how accurately a light source can render the colors of objects compared to natural daylight. It is an important factor in determining the quality and appearance of colors under a given light source.
Color Temperature: Color temperature is a numerical measure of the hue of a light source, expressed in kelvins (K). It provides a way to describe the warmth or coolness of a light, with lower color temperatures appearing warmer (more yellow/red) and higher color temperatures appearing cooler (more blue).
De Broglie wavelength: The de Broglie wavelength is the wavelength associated with a particle and is inversely proportional to its momentum. It highlights the wave-particle duality of matter.
Electromagnetic Radiation: Electromagnetic radiation is a form of energy that is transmitted through space or a medium in the form of electric and magnetic fields oscillating perpendicular to each other. It encompasses a wide range of wavelengths and frequencies, from radio waves to gamma rays, and plays a crucial role in various physical phenomena and applications.
Fluorescent: Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a type of luminescence where the substance absorbs energy, typically in the form of ultraviolet or visible light, and then re-emits the energy as visible light. This process occurs due to the electronic structure of the fluorescent material and is a fundamental concept in the understanding of color and color vision.
Hering Theory: The Hering theory, also known as the opponent-process theory, is a model of color vision that explains how the human eye and brain perceive and process color information. It proposes that the visual system contains three pairs of opponent color channels that respond to different wavelengths of light, allowing for the perception of a wide range of colors.
Hues: Hues are the distinct characteristics of color that differentiate one color from another, often described as shades like red, blue, or green. In physics, hues correspond to specific wavelengths of visible light.
Hydrogen spectrum wavelength: The hydrogen spectrum wavelength corresponds to the specific wavelengths of light emitted or absorbed by hydrogen atoms when electrons transition between energy levels. These wavelengths form a series of spectral lines that are fundamental to understanding atomic structure.
Incandescent: Incandescent refers to a type of light source that generates light by heating a filament, typically made of tungsten, to a high temperature until it glows and emits visible light. This process of producing light through thermal radiation is the fundamental principle behind incandescent lighting.
L-cones: L-cones, or long-wavelength sensitive cones, are one of the three types of color-detecting photoreceptor cells found in the human retina. They are responsible for detecting and processing red-orange wavelengths of light, contributing to our ability to perceive color and color vision.
Light-Emitting Diodes: A light-emitting diode (LED) is a semiconductor device that emits light when an electric current is passed through it. LEDs are widely used in various applications, from displays and indicators to lighting and signage, due to their energy efficiency, long lifespan, and versatility in color options.
M-cones: M-cones, or medium-wavelength sensitive cones, are one of the three types of color-detecting photoreceptor cells in the human retina. They are responsible for perceiving medium-wavelength light, which corresponds to the green portion of the visible light spectrum.
Opponent Process Theory: The opponent process theory is a model that explains how the human visual system perceives color. It proposes that color vision is based on the interaction of three opponent color channels: red-green, blue-yellow, and black-white. This theory suggests that the visual system processes color information in an antagonistic manner, where the perception of one color is accompanied by the inhibition of its opponent color.
Photopic Vision: Photopic vision is the type of vision that occurs under well-lit conditions, primarily facilitated by cone cells in the retina. This mode of vision enables the perception of color and fine detail, making it crucial for activities like reading and recognizing faces. In contrast to scotopic vision, which operates in low-light conditions using rod cells, photopic vision plays a significant role in how humans interact with their brightly lit environment.
Photoreceptor: A photoreceptor is a specialized sensory neuron found in the retina of the eye that is capable of phototransduction - the conversion of light energy into electrical signals that can be interpreted by the brain. Photoreceptors are crucial for the processes of vision and color perception.
Retinex theory of color vision: Retinex theory of color vision explains how the human visual system perceives colors consistently under varying lighting conditions. It suggests that the brain compares different areas of the retina to maintain color constancy.
Retinexes: Retinexes are theories of color vision that explain how the human brain perceives colors under varying lighting conditions. They suggest that the brain compares information from different parts of the retina to maintain consistent color perception.
Rods and cones: Rods and cones are photoreceptor cells in the retina of the eye responsible for vision. Rods are sensitive to low light levels and do not perceive color, while cones detect color and function best in bright light.
S-cones: S-cones, or short-wavelength cones, are photoreceptor cells in the human retina that are sensitive to blue light. They play a crucial role in color vision by responding to wavelengths of light around 420 nm, which allows us to perceive colors in the blue spectrum. These cones work together with M-cones and L-cones, which are sensitive to medium and long wavelengths, respectively, to create a full range of colors that we see.
Scotopic Vision: Scotopic vision refers to the visual perception that occurs in low-light conditions, primarily mediated by the rod photoreceptors in the retina. This type of vision is crucial for adapting to dimly lit environments and allowing us to see in the dark.
Simplified theory of color vision: The simplified theory of color vision explains how the human eye perceives color based on the presence of three types of photoreceptor cells in the retina, each sensitive to different wavelengths of light. This theory forms the basis for understanding color perception in terms of red, green, and blue primary colors.
Spectrum: A spectrum is the distribution or range of different wavelengths or frequencies of electromagnetic radiation, often displayed in the order of their wavelengths or frequencies. It is a fundamental concept that underpins the understanding of various phenomena related to light, color, and the nature of the universe.
Subtractive Color Mixing: Subtractive color mixing is the process of combining colored light sources, such as pigments, dyes, or filters, to create new colors by selectively absorbing or subtracting certain wavelengths of light. This is in contrast to additive color mixing, where colored light sources are combined to create new colors.
Trichromatic Theory: The trichromatic theory is a model that explains human color vision. It proposes that the retina contains three types of color-sensitive receptors, each responding maximally to different regions of the visible light spectrum, which allows the brain to perceive a wide range of colors.
Visible light: Visible light is a portion of the electromagnetic spectrum that is visible to the human eye, encompassing wavelengths from approximately 380 nm to 750 nm. It is responsible for the perception of colors.
Visible Light: Visible light is the portion of the electromagnetic spectrum that is visible to the human eye. It is the only form of electromagnetic radiation that can be directly perceived as light, enabling us to see the world around us.
Wavelength: Wavelength is a fundamental characteristic of waves, representing the distance between consecutive peaks or troughs in a wave. It is a crucial parameter that describes the spatial extent of a wave and is closely related to other wave properties such as frequency and speed.
Young-Helmholtz theory: The Young-Helmholtz theory, also known as the trichromatic theory, is a model that explains human color vision by proposing that the retina contains three different types of color-sensitive receptors, each responding to a different range of wavelengths of visible light.