Radiometry and Photometry

Radiometry is the science of measuring electromagnetic radiation in the “optical range,” namely, frequencies (or wavelengths) in the range 3 × 10¹¹ Hz (or 1000 μm) to 3 × 10¹⁶ Hz (or 0.01 μm). This range includes the infrared (IR), visible and ultraviolet (UV) regions of the electromagnetic spectrum. For a proper understanding of the ideas of radiometry, it is imperative that we understand certain concepts like projected area and solid angle.