Light energy is energy carried by electromagnetic waves that are visible to the human eye. It is a narrow slice of the electromagnetic spectrum. Wavelengths from about 400 to 700 nanometers. Violet at the short end. Red at the long end. In between, all the colors of the rainbow.

Light behaves as both a wave and a particle. The particle is the photon. A photon carries a quantum of energy. The energy depends on the frequency. Blue light has higher frequency and more energy than red light. That is why ultraviolet light can damage skin and infrared light only warms it. The energy is in the photon.

Sources and uses of light energy

• The sun: nuclear fusion produces light.
• Light bulbs: electrical energy becomes light.
• LEDs: efficient conversion of electricity to light.
• Fire: chemical energy becomes light and heat.
• Bioluminescence: living organisms produce light.

Light energy drives photosynthesis. Plants capture photons and convert their energy into chemical bonds. That energy feeds almost every ecosystem on Earth. Light energy also drives solar panels. Photovoltaic cells convert photons directly into electricity. The efficiency depends on the material and the wavelength. Silicon panels capture a broad spectrum but waste much of the energy as heat. Tandem cells stack layers to capture more. Light is the most abundant energy source on the planet. It arrives every day, free of charge. The challenge is capturing it and storing it. Batteries help. But the sun does not shine at night. That is the fundamental problem of solar energy. Light is abundant. It is also intermittent.