# The wavelength region of the IR sensor

I was reading an article that explains the Infrared sensor until I came to the wavelength region's section, which has been mentioned as the following:

The infrared waves typically have wavelengths between 0.75 and 1000µm.

a- The wavelength region from 0.75 to 3µm is known as the near infrared region.

b- The region between 3 and 6µm is known as the mid-infrared region, and

c- infrared radiation which has a wavelength greater higher than 6µm is known as far infrared.

I have searched for an image that shows those numbers, and I found this one: I have transformed the µm's values to m, but they didn't fit to the numbers shown in the image. So, what's wrong?

A side-note: I took into consideration that that image is wrong, and I found this one, but I don't think it is right either.

My calculations:

0.75µm and 1000µm = 750nm and 1000000nm = 0.75x10^-6m (= 7.5x10^-7m) and 1x10^-3m (= 0.001m)

3µm = 3000nm = 3x10^-6m

6µm = 6000nm = 6x10^-6m

• I don't get it. What do you think doesn't make sense? Everything you write is correct and according to both images. – pipe Oct 28 '18 at 20:50
• @pipe - I don't think the ranges that are mentioned in a, b, and c, are in the IF wavelength's range. – Tasneem ZH Oct 28 '18 at 21:03
• 750 nm = 0.75 micrometers – JRE Oct 28 '18 at 21:12
• @Felthry: Fixed. – JRE Oct 28 '18 at 21:17
• @JRE If that means those numbers are in the Visible Area. Then how come it starts from 750 to 300 (in a) when 300 is not in that range? And then it starts from 300 to get back to 600 (in b)? And so on (in c) ... – Tasneem ZH Oct 28 '18 at 21:23

As with most SI units it is convenient to quote our dimensions in values of 1 up to 999 followed by the multiplier (mΩ, kΩ, MΩ etc.). As we can see from your graph the visible light spectrum is in the range 400 nm to 750 nm. To keep the units consistent we often refer to the IR wavelengths in nanometers as well.

The infrared waves typically have wavelengths between 0.75 and 1000µm.

This is 750 nm up.

a - The wavelength region from 0.75 to 3µm is known as the near infrared region.

So 750 nm to 3000 nm.

b - The region between 3 and 6µm is known as the mid-infrared region, and

3000 nm to 6000 nm.

c - infrared radiation which has a wavelength greater higher than 6µm is known as far infrared.

At this stage it's probably worth switching to μm.

Figure 1. Section of OP's image with wavelengths marked in nanometers.