850 or 940?
850nm is the standard IR Illuminator, this has the small red glow and maybe seen by some animals. 850 gives the most range of the 2 options.
If you are hunting rats, foxes (don't have them in NZ :)) stoats etc that are nocturnal animails then 940 is of benefit for sure, likewise touchy rabbits
940nm is a higher wavelength and is not visible to animals; its sometimes called stealth or covert - it doesn't have the red glow, but the trade off is less range and it is grainier
Can I have both - No not in the PARD devices itself; you have however use an external torch in the other wavelength to cover all your bases of range, size and stealth
Are they really invisible to animals - yes and no
Think about it this way in laymans terms
White Light - If I Punch you in the face, you see my fist coming and feel the impact
IR Light - You don't see my fist coming but you get hit and feel the impact
That energy is still there even if you can't see it - you will feel something odd
Also animals generally have massive ears compared to us and are on alert all the time - your bolt, noise from movement etc often will give you away and yeah they will look straight towards you
So what should I do
Hunting those touchy animals 940nm
Use only the power level you need - level 3 on a animal at 50m is like looking at your car headlights ... gunna feel something ...
Keep quiet
Here is a video comparing both Lights on the Same scope