[taneq]

Great read! I'm curious about the last bit, saying you need liquid nitrogen cooling to detect the radiated heat from a human. I'd always thought some snakes have infrared-sensitive spots near their mouths that could sense mammals from a distance, are they just that much more sensitive than a photodiode? Or are they sensing something else?

[yk]

No idea about snakes, but a sensor will glow itself at these wavelength, since it has room temperature which is basically the same temperature as body temperature. So to stop the sensor from blinding itself, you need to cool it significantly below the temperature you want to see.

[venomsnake]

Snakes are seeing in the closest to visible specter IR IIRC. Also they have evolved a lot of other sensory mechanisms to detect pray - sounds, vibrations, taste

[adrianN]

https://en.wikipedia.org/wiki/Infrared_sensing_in_snakes

They can sense radiation between 5 micrometers and 30 micrometers.

[taneq]

Wow, so instead of a photochemical or photoelectric effect, it's actually literally a heat sensor - as in, radiation from the environment heats the interior of the heat pit (which is cooled by the snake's blood to maintain a baseline) and it is this change in temperature that is detected?

I wonder if the ribbonfarm guy could use a variant of this for his pixel scanner thing?

[ambicapter]

That is the operating principle of a bolometer.