Overview
This lecture explains how human vision perceives color, highlighting the difference between the physical properties of light and color perception in the brain.
Physical vs. Perceived Color
- Light is a type of wave, and its color is determined by its frequency.
- High-frequency light waves appear violet, low-frequency appear red, and other frequencies correspond to other colors.
- Physical color refers to color as a property of light itself, independent of human perception.
- Overlapping red and green light creates a yellow region, even though there is no yellow-frequency light present.
Human Color Perception and the Retina
- The retina is a thin layer of cells at the back of the eyeball that detects light.
- Two types of cells in the retina: rods (for low light) and cones (for color).
- There is one type of rod cell and three types of cone cells (red, green, blue).
- Each cone cell type sends a distinct signal to the brain based on the light it detects.
How Mixed Light Creates Color
- Yellow light (with yellow frequency) activates both red and green cones; there is no dedicated yellow cone.
- A mixture of red and green light also activates the same cones, producing the same signal to the brain as yellow light.
- The brain perceives yellow whether the light is true yellow or a mix of red and green frequencies.
Color Vision Limitations and Applications
- In darkness, only rod cells are active, so color cannot be detected.
- Humans can be fooled into seeing any color by mixing the right combination of only red, green, and blue light.
- TVs use only red, green, and blue lights to simulate all visible colors.
Key Terms & Definitions
- Physical color — color as a property of light's frequency, not dependent on perception.
- Retina — layer of light-detecting cells at the back of the eye.
- Rod cells — cells in the retina responsible for vision in low light; detect brightness only.
- Cone cells — retinal cells responsible for color vision; three types (red, green, blue).
- Color perception — the brain's interpretation of signals from cone cells, producing the experience of color.
Action Items / Next Steps
- Review the structure and function of the retina, rods, and cones.
- Understand how red, green, and blue light can combine to form all visible colors.