Overview
This lecture explains the nature of light, its sources, the electromagnetic spectrum, how light relates to color, and how we perceive colors in the world.
What is Light?
- Light is a type of energy that travels in waves and is produced when matter gains energy.
- This energy is called electromagnetic radiation.
- Visible light is just one part of the electromagnetic radiation spectrum that human eyes can detect.
The Electromagnetic Spectrum
- The electromagnetic spectrum includes visible light, radio waves, microwaves, x-rays, gamma rays, and more.
- All types of electromagnetic radiation travel as waves but have different wavelengths and energy levels.
- Light with longer wavelengths (e.g., radio waves) has less energy; shorter wavelengths (e.g., gamma rays) have more energy.
- Scientists use special tools to detect and measure invisible parts of the spectrum.
Visible Light and Color
- Visible light is a small section of the electromagnetic spectrum and contains all colors we can see.
- Sunlight appears white but contains all visible colors, which can be separated by a prism.
- When light passes through a prism, it bends and spreads into different colors due to different wavelengths.
Rainbows and Color Order
- Rainbows form when water droplets act like prisms, bending sunlight into different colors.
- The seven main colors of a rainbow are red, orange, yellow, green, blue, indigo, and violet, always in the same order.
- Red has the longest wavelength; violet has the shortest.
Light Beyond the Visible Spectrum
- Infrared light has a longer wavelength than visible red and is invisible to humans.
- Ultraviolet light has a shorter wavelength than visible violet and is also invisible.
How We See Color
- Objects appear colored due to the wavelengths of light they reflect.
- A green leaf appears green because it reflects green light and absorbs other colors.
- White objects reflect almost all visible light; black objects absorb most of it.
Key Terms & Definitions
- Light — energy that travels in waves as electromagnetic radiation.
- Electromagnetic Spectrum — the full range of electromagnetic radiation, from radio waves to gamma rays.
- Wavelength — the distance between wave peaks, related to energy level.
- Visible Light — the range of electromagnetic radiation detectable by human eyes.
- Prism — an object that bends and separates light into its component colors.
- Infrared — electromagnetic radiation with a longer wavelength than visible red light.
- Ultraviolet — electromagnetic radiation with a shorter wavelength than visible violet light.
Action Items / Next Steps
- Observe objects around you and identify the colors you see and consider their reflected wavelengths.