Understanding Infrared Thermography Reading 7 Part 2 of 2.pdf

A.3 The Basic Physics of Infrared Radiation and Sensing
All targets radiate energy in the infrared spectrum. The hotter the target, the
more energy is radiated (∝T 4 ). Very hot targets radiate in the visible as well,
and our eyes can see this because they are sensitive to light. The sun for
example, at about 6000 K, appears to glow white-hot; a tungsten filament, at
about 3000 K, has a yellowish glow, and an electric stove element, at 800 K,
glows red. As the stove element cools, it loses its visible glow but it continues
to radiate. We can feel it with a hand placed near the surface but we can’t see
the glow because the energy has shifted from red to infrared. Infrared
detectors can sense infrared radiant energy and produce useful electrical
signals proportional to the temperature of target surfaces. Instruments that
use infrared detectors and optics to gather and focus energy from the targets
onto these detectors are capable of measuring target surface temperatures
with sensitivities better than 0.1°C, and with response times as fast as
microseconds. Instruments that combine this measurement capability with
capabilities for scanning the target surface are called infrared thermal imagers.
Charlie Chong/ Fion Zhang