Night Vision

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Night Vision:

As was mentioned in an earlier blog, there are two types of cells in the eye that detect light: Rods and Cones.

• Cones are for bright light and colour vision. Rods are for night vision and detecting motion in our peripheral vision.

• Rods are very sensitive to small amounts of light because they have a high amount of pigment to absorb light and because there are many more rods than cones.

Night Vision Goggles (NVG)

There are multiple steps to NVG function:

• First, light is gathered
• Sensors detect small amounts of light that are reflected off objects (this includes low levels of infra-red light which is not visible to the human eye)
• Then, light is amplified
• Just like turning the volume up on a stereo, the small amounts of light are made brighter
• Finally, an image is projected
• The new amplified image is shown on a small LCD screen

Since night vision goggles are sensitive to infra-red light, objects that give off a lot of heat will appear very bright (ex. light bulbs and headlights)


Humans vs. Animals:

Human night vision is very poor compared to most animals. This is because a lot of animals have an extra layer in the retina called tapetum lucidum

• This extra layer reflects light within the eye, basically making it more intense (kind of like NVGs)
• It is also the reason why we see different coloured reflections through the pupil of most animals

FAQ:
Q: What if a person had only rods, and no cones?
A: This person would be completely colour blind because rods cannot detect colour. They would also have very poor vision since cones are needed for central vision.

Q: How many rods are there in the retina?
A: There are approximately 120 million rods and about 7 million cones. Cones are packed tightly in a tiny central area called the macula. Rods are spread out over the rest of the retina.

Q: Do night vision goggles always show a green image?
A: Yes. This is done deliberately because human vision works best with greens and yellows.

Q: Can I get night vision goggles?
A: Yes, but don't expect them to be as cool as what you see in movies. Goggles that are available to consumers are older technology and lower quality. The newer, better stuff is reserved for military use only!

Q: Can I get tapetum lucidum?
A: Not unless you plan on stealing a raccoon's eyes. Good luck.

As always, thank you for reading. Please feel free to pass this information on to anyone who may find it useful. Questions, comments, and suggestions are welcome.