Why visible IR diodes are important for an IR heat pad to fully do its job

There are many products marketed as IR heat pads. Not all of them actually give much of a benefit compared to normal hot-wire conductive heat pads. This is how a vacuum pump should look, wrapped in an actual IR heat pad:

The visible red light here is 660nm wavelength red light, which technically isn't infrared. What you can't see in the image is that the heat pad is shining even more brightly in the near infrared wavelength of 850nm.

The skin and water contained in the skin and interstitial fluid is highly absorbent for visible light frequencies in the 380-600 nm range (from violet blue to orange-reddish), but from 600 nm and upwards in wavelenghts skin absorption drops , so red light 625-750 nm and near infrared light 750-1300nm can penetrate very deeply without being absorbed. Even in the NIR range there are important differences: skin penetration decreases above 900nm. The most effective range is between 810 and 870nm, and most ""real" IR heat pads therefore work with 850nm. 660nm is a wavelength often mentioned, because it’s near the end of the visible spectrum (red light): its penetration depth though doesn’t exceed 3mm, so it can be effective for skin treatment (e.g. Wrinkle reduction) but not much for PE.

Here's a quote from an insightful post about IR on Thunder's Place:

NIR irradiation directly triggers cellular division and growth. It’s important to understand it’s a very different approach from traditional heating solutions (ultrasound and far infrared – I don’t even consider heating pads or other solutions based on conduction). Growth by heating works by entering a range of temperatures (usually >40°) where the collagen matrix destabilizes and gets plastic deformation. Then, during a rest period real growth slowly happens (as it always happens in tissues) in this new elongated form.
NIR radiation interacts through photoreceptors present in cells, such as cytochromes or other photosensitive proteins: when infrared light is absorbed by these photoreceptors, it triggers a series of biochemical reactions that influence cellular metabolism, proliferation and differentiation. For example, infrared light activates intracellular signaling pathways, such as those mediated by transcription factors, which regulate gene expression and therefore directly affect cell growth.

Source: https://thunders.place/penis-enlargement/why-near-infrared-is-better-than-fir-and-us.html?highlight=infrared

(Do read that thread - it goes into a lot more detail than I do here. )

So, not only do we want heat to help break down hydrogen bonds between collagen fibrils to make them easier to plastically deform at lower tension, we also want it to trigger cellular photoreceptors to help stimulate the release of growth factors.

Many so-called IR heat pads today come with a "hygienic washable cover" - i.e. a layer of relatively thick textile what completely covers the IR diodes. The conclusion about the effectiveness of such "IR heat pads" should be quite easy to make, knowing the above. The layer of fabric will not let much 850nm IR light through, even if there are diodes operating at that frequency beneath it. Therefore, such a heat pad will work on the principle of being just a hot object - such as a normal electric heat pad with hot wires inside, or a sock full of rice, etc. I'm sure 1-10% of the IR light slips through the fabric if it's not too tightly woven, but unless they have managed to make the fabric magically transparent to IR, it will simply convert the IR to normal warm surface heat, that can be conducted where the fabric is touching, but will not effectively transmit to your skin without touch. They might be able to get your peepee up to temperature, but your skin will get uncomfortably hot compared to your tunica albuginea, which is deeper.

So, when you buy a heat pad, if you aim for the full benefits of IR irradiation, go for ones where you can see the IR diodes, and which operate in the ~850nm range. If they also have some 660nm red light this is not detrimental - it does heat you to a small extent and has some benefits for the skin - but definitely avoid products that only operate at 660nm.

Also: Don't trust me. Do your own research, and do have a look at the tread I linked on Thunder's Place. And while you're there, also read the thread "Hanging with FIRe" which deserves some kind of PE hall of fame status. It goes over the very clear benefits of using heat to modify the properties of the collagen fibrils of the tunica albuginea.

https://thunders.place/penis-hangers/hanging-with-fire.html