Overview
This lecture explains why objects appear certain colors, discussing how visible light interacts with materials and the roles of absorption, reflection, transmission, and color filters.
Visible Light and Color Spectrum
- Visible light consists of a spectrum of colors from red (longest wavelength, lowest frequency) to violet (shortest wavelength, highest frequency).
- The acronym ROYGBIV helps remember the color order: Red, Orange, Yellow, Green, Blue, Indigo, Violet.
- White light contains all wavelengths; black is the absence of light.
How Objects Get Their Color
- The color an object appears depends on the wavelengths of light hitting it and the object's properties.
- Opaque objects do not transmit light; their color is determined by reflected wavelengths.
- An object appears a certain color if it reflects those wavelengths and absorbs the rest (e.g., a blue object reflects blue light).
- Some objects appear a color by reflecting a combination of wavelengths (e.g., yellow can be reflected yellow or both red and green).
Transparent and Translucent Objects
- Transparent objects transmit nearly all light, allowing us to see through them (e.g., window glass).
- Translucent objects transmit some light; the more they transmit, the clearer we see through them.
- A translucent object's color depends on which wavelengths are transmitted most (e.g., a green bottle transmits green light).
Color Filters
- Color filters allow only specific wavelengths to pass through while absorbing the rest.
- A primary color filter (red, green, or blue) only transmits that primary color.
- White light through a green filter lets only green wavelengths through; white paper appears green, but a blue object would appear black through this filter.
- Filters of secondary colors (like yellow or indigo) transmit both their color and the relevant primary colors that combine to make that color (e.g., yellow filter passes red and green).
Key Terms & Definitions
- Opaque — Object that does not transmit light; color is from reflected light.
- Transparent — Object that transmits almost all light; appears clear.
- Translucent — Object that transmits some light; appears semi-clear or frosted.
- Color filter — Material that only allows specific wavelengths of light to pass while absorbing others.
- Primary colors (light) — Red, green, and blue; fundamental for creating other colors by combination.
Action Items / Next Steps
- Review the order of the visible light spectrum using ROYGBIV.
- Practice identifying the type (opaque, transparent, translucent) and color behavior of household objects.