Seeing in darkness

efreysson said:

I want to give a character superhuman night vision, and I'm wondering how far I can go and how to make the mechanics of it work.

I know thermal imaging is a thing, but what is the difference between multicolour Predator-style vision, and white/grey vision? I've seen videos of both. And would either of these be in any way effective in, say, navigating a basement where there is no light or heat at all?

Basically, IS there a way to see in complete darkness?

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Some kind of echo location?

Wouldn't thermal imaging be a problem with homeothermic animals? Sensory systems using visual pigments to detect infrared would have to be shielded from interference.

Snakes that detect heat have thermosensitive pit organs that send impulses to the optic centres of the brain, rather than detecting infrared directly through optic cells. (I think.) But if optic cells were able to detective infrared, I suspect the images would be monochrome -- the stronger the signal, the brighter the image. A visual system in which different temperatures were represented by different colours, would require a range of cells with different pigments sensitive to different intensities of light.

(I haven't thought this through at all.)

Oh, I just remembered the deep sea dragonfish, Malacosteus, that emits infrared light to illuminate prey. They prey is blind to IR, but so is the dragonfish. So it converts the IR into a shorter wavelength.

https://biolum.eemb.ucsb.edu/organism/dragon.html

And here's a pic of the fish: http://fishesofaustralia.net.au/home/species/4770

But reading that description, it says that one group of deep sea fish actually have IR sensitive visual pigments. Strange creatures!

Tapetum is an easy fix, but requires some ambient light to work. Maybe that plus the heat-sensing pit organs some snakes have, and you'll get pretty far.

Fantasy aside, there are three types of night vision devices that are generally used. Light amplification, active infrared, and passive infrared. Light amplification, i.e. Starlight scopes and night vision goggles require some degree of light, and they don't work well without some moon light. They are portable. Active IR uses an invisible IR light source to cast a beam forward, to be sensed by goggles or some sort of scope. They require no visible light, but have a fairly short range and can be detected by other IR sensor devices. Passive IR can also see in total darkness, does not require a cast IR beam, and can have quite a long range. Passive IR devices are however not very portable as they use a cryogenic cooling system for the internal IR sensor. A portable device will be heavy, and require expendable bottles of compressed gas. A not portable device, such as a tank night vision sight, will have an internal compressor to cool the IR sensor.

efreysson said:

This sounds like what I need, ie the ability I need to give to my character. Can you tell me more. Is this the white/grey vision?

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Light amplification is typically displayed as greenish white vision. Passive infrared, particularly the newer generation FLIR imagery is displayed as white/grey but the systems I've worked with display yellow and red on black images. Warm objects like people and animals show up very well, although detail isn't displayed. You can generally see building outlines, vehicles, etc... but most background objects at ambient temperature don't stand out well. You can even sometimes make out people inside of wooden buildings - at least the night sights on IFV's could. Tanks too I'm sure.

Take a look at the night tracker on the Dragon missile system. http://www.inetres.com/gp/military/infantry/antiarmor/M47.html

The sketches are crude, but you can get an idea of the size of it in the link. I can't find a photo. It weighs about 25 lbs, and is about as small as you can make a passive IR device. Unlike a single missile and a day tracker, it is not something you can lug around on foot easily.

Search Youtube for FLIR imagery and you should get some good examples of what this stuff looks like.

You don't need to see in infrared to see in the dark. As any photographer using one of the newest DSLRs from Canon or Nikon can tell you, it's all about the device doing the seeing. So, think about it in terms of optics. In astronomy, a large mirror captures more photons, right? So you could give your character enlarged eyes (huge retina will do it). Or, as an alternative, you can go the "feline" route: make the retina more sensitive at night and alter the pupil; the reason cats have a weirdly shaped pupil when it is contracted is that their retinas are very sensitive to photons. They have to shut out almost ALL of the light when it gets bright, as opposed to most mammals. Either way, it's not a stretch.

"Complete darkness" is a relative term. Do you mean the blackness of space? Or the absence of moonlight on Earth?

efreysson said:

Basically, IS there a way to see in complete darkness?

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No. Sight requires some sort of light radiation. The difference between the black and white versus the multi-color is how Hollywood created the effect. Different sensors and screens produce different effects, gray, green, reddish, whatever. Computers can interpret this for the human eye.

That said, there is almost always light. Night vision works through light amplification, starlight, candle light, etc. Infrared works through transmission of an infrared light and the system picks up the infrared and transmits it to the eyes with normal light rays through a viewing screen. Ultraviolet is possible but not technically, or practically, feasible. There are animals, including birds, that can see in this wavelength but humans have eyes that are way too big.

Want to see in total darkness? Bring a flashlight. Infrared so it can't be detected works okay, but you need to see in infrared or have a system that can. As mentioned, there are other senses that can work, such as hearing, taste, feel and smell. Since the guy is superhuman, just give him the ability to see in the dark. No need to explain it, he's not based in reality to begin with.

Jeff