IR illuminators: 850nm or 940nm?

Fox shot using IR for population control

This fox a few years ago was well aware of 850 IR so I switched to 940 and reduced likely range - Credit: Chris Parkin

You've probably seen two types of IR illuminators - 850nm and 940nm. But what's the difference and which should you choose!?

I understand that two types of IR illuminators are available – 850nm and 940nm. What’s the difference?

CHRIS PARKIN replies: The difference is the frequency of the infrared light illumination and its suitability for the scenario. With like-for-like illuminators, the 850nm will give you greater range to the quarry, but the light is visible to the naked eye of both human and animal.

It may be very little (and never stare directly into illuminators) but some shooters are concerned that the quarry may see and react to the 850 light. They are, however, oblivious to 940. Personally I have found that foxes around my land used to be a lot twitchier around the 850 than they are now, almost entirely ignoring it. I think this could be to do with increasing use of thermal sporters to display position, whereas when NV was first around we used almost exclusively to scan and locate quarry, thereby forewarning it.

I may be wrong, but that’s how it seems to me around here, as foxes that are just as wily about noise, scent and movement seem to be inquisitive about the IR source, rather than afraid of it. Maybe it’s because they (hopefully!) only see it once and have less opportunity to associate it with loud bangs or, worse still, non-fatal wounding, as they used to do with regular visible lamps.