Thermal radiation and visible light are both forms of electromagnetic radiation, but they differ primarily in their wavelength range and the way they are perceived by human senses.
Thermal radiation, also known as infrared radiation, is electromagnetic radiation emitted by objects due to their temperature. It is typically associated with the heat energy possessed by objects. The wavelength range of thermal radiation spans from approximately 1 micrometer (μm) to 1000 μm, encompassing the infrared region of the electromagnetic spectrum. This radiation is not visible to the human eye unless it is converted into visible light through special instruments or sensors, such as thermal cameras.
Visible light, on the other hand, refers to the portion of the electromagnetic spectrum that is visible to human eyes. It ranges in wavelength from approximately 400 to 700 nanometers (nm). This range corresponds to different colors, with shorter wavelengths appearing as violet and longer wavelengths appearing as red. Visible light is emitted or reflected by light sources and objects and is responsible for our sense of vision.
The key difference between thermal radiation and visible light lies in their wavelengths and how we perceive them. Thermal radiation is longer in wavelength and falls within the infrared range, while visible light is shorter in wavelength and falls within the range visible to the human eye. Although both forms of radiation are part of the larger electromagnetic spectrum, they are distinguished by their different wavelengths and the sensory experiences associated with them.