Infrared (IR) radiation has longer wavelengths than visible light.
- Visible light: ~380 nanometers (violet) to 750 nanometers (red)
- Infrared radiation: starts just beyond red light at about 750 nanometers and extends up to 1 millimeter
Because IR wavelengths are longer:
- Their frequency is lower than visible light.
- Each IR photon carries less energy than a photon of visible light.
- IR is invisible to the human eye but can be detected as heat by special sensors.
In short, visible light is a narrow band our eyes can detect, while infrared is a “longer wave” region just beyond it.