Learning Infrared Radiation Fundamentals

Definition and electromagnetic spectrum relationship

Infrared (IR) is electromagnetic radiation with wavelengths longer than visible light but shorter than microwaves. It is commonly defined as starting just beyond the red edge of the visible spectrum (about 780 nm) and extending to roughly 1 mm (300 GHz), though there is no single universally accepted boundary. As part of the electromagnetic spectrum, IR occupies the region between visible light and microwaves, and it carries energy and momentum like other electromagnetic radiation. IR is closely related to thermal phenomena and molecular energy transitions. Almost all black-body radiation from objects near room temperature falls in the IR band, and IR emission/absorption occurs when molecules change rotational-vibrational motion, making IR useful for studying molecular energy states. The IR band is also subdivided differently depending on standards and applications (e.g., near-, short-, mid-, and long-wavelength IR; or CIE/ISO schemes), reflecting that different sensors and scientific uses operate over different wavelength ranges.

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Nature of infrared in sunlight and Earth

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