FLIR TG165 Infrared Thermometer TG165 Information Guide

TG165 Imaging IR Thermometer – How it Works

Thermal imaging is one of the most powerful technologies ever developed 

to enhance visual perception. The unaided human eye can only perceive a 

very narrow band of visible light along the electromagnetic spectrum, which 

also includes radio and microwaves, infrared and ultraviolet light, X-Rays, and 

gamma rays. 
Thermal energy—or “heat”—resides within the infrared spectrum, which 

is invisible. However, a spot thermometer sensor is capable of converting 

thermal energy into a temperature measurement, and a thermal imaging 

detector converts thermal energy into an electronic thermal image that can be 

viewed on an LCD screen.
The TG165 utilizes both of these types of infrared technology, simultaneously. 

The spot thermometer emits a beam of infrared light that lands on an object 

and then bounces back. The thermometer determines the object’s apparent 

surface temperature based on how much thermal energy the object is 

emitting, refl ecting, or transmitting. 
The TG165’s thermal imager, on the other hand, includes a micro thermal 

camera that can passively scan an area and display images of hot and cold 

patterns on an LCD screen. Being able to “see” infrared radiation creates an 

entirely new level of awareness for professionals and consumers, alike. Users 

no longer have to guess where to take temperature readings. They can literally 

see hot and cold spots, making work more effi cient and reliable. 
The TG165’s IR thermometer has a Distance‐to‐Spot ratio of 24:1. In other 

words, from a distance of 24 inches (61 cm), the TG165 can measure the 

temperature of a one-inch spot (2.5 cm). If you double the distance to 48 

inches (122 cm) the spot diameter will expand to two inches (5 cm), and so on.
The amount of thermal energy emitted by an object depends upon its 

temperature and how effi ciently it radiates thermal energy. This effi ciency 

is called “emissivity.” Emissivity values range from 0.1 for very refl ective 

material—such as shiny metal—to 1.00 for a pipe with a fl at black fi nish. The 

TG165 has both adjustable and preset emissivity settings, and the TG165 user’s 

manual includes a list of common materials and their respective emissivity 

factors as a quick reference for users who are not trained in thermography.

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