Chinese NIR pad: Initial measurements

Hi everyone.

My NIR pad from Aliexpress has arrived today and I’ve spent some time taking measurements.

It is a cheap one (24 x 12 cm). You can see it in the link below

https://www.ali express.com/ite … SmartRedirect=y

A pad this size is perfect for how I plan to use it, but the measurement results have been a bit dissapointing.
Based on the specs, I should expect 100 mW/cm2 at 0 distance, but the measurements taken show it is significantly below that:

More details in the next post.

Here the measurements I took:

660 nm, 0 cm distance: 32.62 mW/cm2
660 nm, 1 cm distance: 4.34 mW/cm2
850 nm, 0 cm distance: 61.7 mW/cm2
850 nm, 1 cm distance: 10.28 mW/cm2
660 nm + 850 nm, 0 cm distance: 82.67 mW/cm2
660 nm + 850 nm, 1 cm distance: 13.07 mW/cm2

When pushing the meter a bit against the pad, the numbers go higher, but readings become significantly unstable.

Next step is looking at the spectrum.
I am not spending the money on a proper spectrometer, so I bough a Triad module from Sparkfun.

I expect to have some results in a couple of days.

This pad has a ratio of 1:1 of the LEDs 660 nm/850 Nm.

There are others with a ratio 1:2 which means 1 LED with 660 nm and 2 LEDs with 850 nm in one spot. These are the ones which are recommended.

Good work

Ok good point.

I’m trying find those with dual 850 nm with same size as the one I’ve got.
The ones I find are much bigger.

https://www.ali express.com/ite … StoreJustForYou

Awesome!

I’ve ordered one of those. Thanks Rocco.
I’ll take more measurements on it once it arrives.

In the meantime I have checked the spectrum of my pad by using a TRIAD module.
The 3 sensors it populates do not provide a full analysis of the espectrum, but they measure at 18 different frequencies or wavelengths between 410 and 940 nm:
410, 435, 460, 485, 510, 535, 560, 585, 610, 645, 680, 705, 730, 760, 810, 860, 900 and 940 nm.

None of those are centered at 660 or 850 nm, but the 645 nm and the 860 nm are close enough to have an idea of what’s going on.

The sensor is about 10 cm away from the pad in the setup.
Measurements taken:

- Pad off
- 660 nm power setting 1
- 660 nm power setting 5
- 850 nm power setting 1
- 850 nm power setting 5
- 660 nm + 850 nm power setting 5

One thing to take in consideration with LEDs and the solar power meter you are using.

I have the same tool you are using and you can have wide range of readings if the eye of the metering tool is precisely aligned with the center of the LED Or not. The peak reading is only found in really small precise spot under 1 x1 mm.

I have those pads which Rocco mentioned. And with type Tbl 120b you can found readings of 210 to 220 mw/cm2

at touch and precise spot. At 1cm distance the readings of course drop to hundreds.

Taking in consideration how sparse these LEDs are laid out there is always significant areas at zero irritance

Hi Kyrpa, good to see you around here.

Yeah I noticed that, at zero distance, a small variation in position has a really big impact on readings.
I wish the Triad could go further up in the spectrum as well, but it is what it is, a 70 bucks spectrometer.

I am running series of trials with urethral temperature recording with different pad configurations at thempment

That’s great.
Will you share your results?
I assume you are on FIR

I will. Strictly limited on NIR.

Brilliant