Submarine control rooms and red light

[robby]

In this Staff Report, Why are red lights used in darkened control rooms and other low-light situations?, the questioner stated:

@Kevin G

I’ve heard for years that red light supposedly doesn’t affect the ability of the human eye to see in the dark (or a “dark-adapted” eye, to be precise). In movies you see submarine control rooms bathed in red light, maybe because it won’t mess up the periscope guy’s night vision (or it looks cool), while BMW uses only red light to illuminate the gauges and dashboard displays of its cars. A couple of my friends are rabid red-light-believers but can’t call on much data to back them up, other than “Well, if BMW says so . . .” Myself, I think it’s a load of hooey that got started somehow and has careened on, urban-myth-like, into present day lore (and car marketing). --Kevin G, Los Angeles, CA.

The reply didn’t address this aspect of the question, but actual submarine control rooms really are either “rigged for red” for at least 30 minutes prior to ascending to periscope depth at night, or the Officer of the Deck (OOD) wears wraparound red “sunglasses” to accomplish the same thing. Prior to beginning the ascent, the control room is “rigged for black,” and the only illumination in the room comes from low-intensity red light from the various gages, controls, and indicators in the room. This is to further assist the OOD in seeing out the periscope, and also prevents light from the control room from being visible at the surface through the periscope optics.

The new Virginia-class subs have non-optical electronic periscopes, I understand, so this may change in the future.

P.S. The lights on my 1992 BMW 235is, BTW, were more orange than red.

[Philster]

So…red lights won’t trigger your eyes to shut off the compensatory chemicals that were triggered in low light situations.

You are operating in near darkness, your eyes pump out chemicals to adapt, but lights might shut down those chemicals…but red light doesn’t.

[jjpdog]

What about bugs? I have a cockroach problem and as soon as I turn on the light they get skittish and hard to smash. When my red light is on (cool drinking atmosphere) they are a lot less alert. I really enjoy the night hunting but would like to know why it works.
jjpdog

[Alex_Dubinsky]

have you tried other colors of dim light? unless cockroaches don’t see well in red light, no reason that that color should be special (good job realizing that the retina mechanism doesn’t necessarily apply to actual perception, only chemistry).

[Myself248]

A few important points need making:

Long-wave red light, 620nm or greater, is picked up by the cones but not by the rods. So a narrow-spectrum red light (like an LED source) is a good way to read maps and charts at night, while preserving your rod-based night vision. It feels a bit weird because only your cones are picking it up, but you get used to that. (Sort of like relearning to drive wearing Blue-blocker sunglasses, because your eyes aren’t used to perceiving motion with one photoreceptor completely inhibited.)

HOWEVER and CONVERSELY:

If you need a flashlight for emergency use that’ll sip meagerly from a battery and produce the maximum response from your eyes, shoot for the peak sensitivity wavelength of your rods, around 505nm. This is in the blue-green part of the spectrum, and blue-green LEDs are more efficient than white LEDs. Such a light will seem brighter under dark conditions, because it’s being picked up by your dark-adapted rods, exploiting your eyes’ night-vision for extra sensitivity. In close quarters, enough photons should reflect off the object you’re interested in that your cones will come into play too, and you’ll enjoy the fine detail resolution that this allows.

Quick summary of Rhodopsin-based night vision from FlashlightReviews.com

Much more in-depth article aimed at pilots

Enjoy!

[Alex_Dubinsky]

whoa!

I like your explanation a lot more than Cecil’s. It makes way more sense if the rods don’t detect red light at all. I was a bit confused why a light that seems bright would not be affecting the photoreceptors.

Does that mean cecil was pretty much totally off the mark?

[Alex_Dubinsky]

*er, I mean Hawk. Cecil is, of course, infallible.

[chorpler]

@Myself248

It feels a bit weird because only your cones are picking it up, but you get used to that. (Sort of like relearning to drive wearing Blue-blocker sunglasses, because your eyes aren’t used to perceiving motion with one photoreceptor completely inhibited.)

What are Blue-blocker sunglasses? Just some type of sunglasses that block out blue light?

If you need a flashlight for emergency use that’ll sip meagerly from a battery and produce the maximum response from your eyes, shoot for the peak sensitivity wavelength of your rods, around 505nm. This is in the blue-green part of the spectrum, and blue-green LEDs are more efficient than white LEDs. Such a light will seem brighter under dark conditions, because it’s being picked up by your dark-adapted rods, exploiting your eyes’ night-vision for extra sensitivity.

So this, unlike using a red light, would ruin your night vision, right?

And I don’t really understand why red light isn’t picked up by the rods. I thought rods were good at picking up dim light, but there’s only one kind of rod so you can’t distinguish colors using just rod-based vision. Are they sensitive to dim light but only if the light has a wavelength of less than 620nm? Sort of like Einstein’s whole photoelectric effect thingamajig, where light below a certain energy won’t cause the effect no matter how bright it is?

Fascinating stuff, BTW. Thanks for posting. I hope you decide to join.