Register to reply

How does IR (infrared) intensity measured

Share this thread:
makovx
#1
May8-12, 10:30 AM
P: 24
Can a lux meter measure infrared intensity like it does for the visible light? I read from somewhere that it cannot. If you have an IR illuminator on in the dark and hold up your 'regular' lux meter to it, it will likely register 0 - an unhelpful and misleading result.

I'm just wondering if there is a filter inside the lux meter that only passes a certain amount of wavelength, and if I can change some of its circuitry in order to have a reading for IR.

I am looking for a cheap way to measure IR intensity. Or, if there is another way to measure infrared intensity (like a relationship between terminal voltage/current and temperature, temperature vs. illumination, etc.) please let me know (:
Phys.Org News Partner Engineering news on Phys.org
UConn makes 3-D copies of antique instrument parts
Amazon worker piloted drone around Space Needle
Five next-generation technologies for positioning, navigation and timing
Yuri B.
#2
May8-12, 12:42 PM
P: 124
Thermometer ?
Mech_Engineer
#3
May8-12, 01:13 PM
Sci Advisor
PF Gold
Mech_Engineer's Avatar
P: 2,242
Lux and Lumens are photopic units weighted based on the response curve of the human eye. The human eye is not sensitive to infrared, therefore you cannot define a lumen for infrared wavelengths.

However, you can define infrared incident energy in radiometric terms such as power per area, e.g. W/m^2. There are instruments that can measure incident infrared energy as well, but you have to be careful in defining the wavelength band you're interested in, and the expected energy levels.

Bobbywhy
#4
May9-12, 03:10 AM
PF Gold
P: 1,881
How does IR (infrared) intensity measured

Your lux meter is meant to measure visible light. It has a light-sensitive detector which, when light strikes it, generates a photocurrent that gets amplified and sent to the (calibrated) meter readout.

Since Infrared energy is just a lower frequency your lux meter may respond to it, but the calibration would not be correct. You would need to find the "spectral response" curve of the lux meter's sensor, and if it does detect the IR band you are interested in, then you would need to re-calibrate the readout to conform to the responsitivity curve. All-in-all, it's not a very useful thing to attempt because it's complicated and may not even work.

Why not just test your lux meter? Place it in the IR beam and see if it reads anything at all. Better yet, get a new meter that is designed to measure IR intensity.


Register to reply

Related Discussions
Has anyone measured the light intensity given off in a fusion reactor? Nuclear Engineering 14
Intensity measured from a point and surface intensity Introductory Physics Homework 4
COMSOL: Integrate intensity field in R^3 to obtain an intensity surface in R^2 Mechanical Engineering 0
Intensity of Near-Infrared Spectroscopy Laser Introductory Physics Homework 7
If visible light have so much more energy than infrared, why does infrared feels hot? General Physics 15