Properties of Light

Understanding the nature of light, color, and the visible spectrum

Topics

How do we see color?

We see color through specialized cells in our eyes called cones that detect different wavelengths of light. There are three types of cones sensitive to red, green, and blue wavelengths. Our brain combines signals from these cones to create the perception of all colors.

How does fluorescence work?

Fluorescence occurs when a material absorbs high-energy light (usually ultraviolet) and re-emits it as lower-energy visible light. The absorbed energy excites electrons to higher energy levels, and when they return to lower levels, they emit light of specific wavelengths, creating the characteristic glow.

What is blackbody radiation?

Blackbody radiation is the electromagnetic radiation emitted by an ideal object (blackbody) that absorbs all incident radiation and emits radiation based solely on its temperature. The spectrum and intensity depend only on temperature, following Planck's law, with hotter objects emitting more radiation at shorter wavelengths.

What is color?

Color is how our eyes and brain perceive different wavelengths of light. Visible light wavelengths range from about 400 nm (violet) to 700 nm (red), with different wavelengths appearing as different colors. Color depends on both the light source and how objects reflect or transmit light.

What is infrared light?

Infrared light is electromagnetic radiation with wavelengths longer than visible red light but shorter than microwaves, ranging from about 700 nanometers to 1 millimeter. It's invisible to human eyes but can be felt as heat, and is emitted by warm objects.

What is the speed of light?

The speed of light in vacuum is approximately 299,792,458 meters per second (about 186,282 miles per second), often denoted as 'c'. It's the fastest speed possible in the universe and is constant for all observers, regardless of their motion.

What is the visible spectrum?

The visible spectrum is the range of electromagnetic wavelengths that human eyes can detect, approximately 400-700 nanometers. It includes all the colors we can see, from violet (shortest wavelength) through blue, green, yellow, orange, to red (longest wavelength).

What is ultraviolet light?

Ultraviolet (UV) light is electromagnetic radiation with wavelengths shorter than visible violet light but longer than X-rays, ranging from about 10 to 400 nanometers. It's invisible to human eyes but has higher energy than visible light and can cause sunburn and fluorescence.

Why is light both a wave and a particle?

Light exhibits wave-particle duality—it behaves as both waves and particles depending on how we observe it. Wave behavior appears in interference and diffraction, while particle behavior (photons) appears in interactions with matter. This duality is fundamental to quantum mechanics.

Why is light the fastest thing?

Light is the fastest thing because it travels at the universal speed limit—the speed of light in vacuum (c = 3 × 10⁸ m/s). According to Einstein's theory of relativity, nothing with mass can reach this speed, and massless particles like photons always travel at this maximum speed.