Radiant energy is energy carried by electromagnetic waves. Sunlight, radio waves, X-rays, and microwaves all qualify. The waves travel through space at the speed of light. They need no medium. That is how the Sun's energy reaches Earth across 150 million kilometers of vacuum.

The spectrum spans a wide range. Visible light occupies a narrow band. Infrared carries heat. Ultraviolet causes sunburn. Each wavelength interacts with matter differently. A solar panel responds to visible and near-infrared light. A radio antenna responds to much longer waves. Human eyes respond only to a sliver of the whole spectrum.

Radiant energy drives life on Earth. Plants capture it through photosynthesis. It warms the planet and drives weather. Solar thermal plants concentrate it to make steam. Solar panels convert it directly to electricity. Understanding the spectrum lets engineers design materials that absorb, reflect, or transmit specific wavelengths.

Key bands

• Radio waves
• Microwaves
• Infrared
• Visible light
• Ultraviolet, X-rays, gamma rays