At what temperature objects start to glow?

[kerbiloid]

20 minutes ago, PB666 said:

why we use red-lights in displays at zoos

and also in submarines (in combat mode) and for emergency lighting, too.

Spoiler

Vampires, lemurs and other creatures of night won't crawl from the darkness of the zoo or submarine and chase us in the red light invisible for them.

Or just because we look at the night animals at low level of illumination, and the human eye adaptation runs much faster between the "red light/daylight" and "red light/darkness" pairs rather than "daylight/darkness".

Edited January 1, 2018 by kerbiloid

[Zeiss Ikon]

15 hours ago, kerbiloid said:

and also in submarines (in combat mode) and for emergency lighting, too.

  Reveal hidden contents

Vampires, lemurs and other creatures of night won't crawl from the darkness of the zoo or submarine and chase us in the red light invisible for them.

Or just because we look at the night animals at low level of illumination, and the human eye adaptation runs much faster between the "red light/daylight" and "red light/darkness" pairs rather than "daylight/darkness".

The main reason red is used for lighting in situations like submarine and ship command centers (during emergencies at night), as well as for necessary lighting at astronomy gatherings and so forth, is that deep red has the least effect on the darkness adaptation of the human eye.  Even a fairly bright red light (one that, for instance, allows reading fine print) won't destroy the eye's ability to see in darkness when the red light is turned off or blocked.  All mammalian eyes, dichromat or not, have reduced sensitivity in red compared to other colors.  Dichromats may have more reduction in that range, I'm not really certain.

Interestingly, some darkrooms (particularly when handling color or panchromatic sensitized materials) use the dimmest possible light -- in green.  This is because the human eye is most sensitive in the yellow-green wavelengths, so the light can be several times dimmer than a red light and still allow, for instance, seeing the forming image in a negative partway through development -- with a minimum of light to add fog to the final product.  The light can be made so dim that it takes many seconds of exposure to have any effect on the film, and a fully adapted worker can still see well enough to adjust a coating machine, inspect a partially developed image, make sure panchromatic printing paper is emulsion side up, etc.  Now, most of these operations are done with IR goggles and illuminators (at least for materials that aren't IR sensitive), but the dim, dim green light was used long before IR and light amplification devices existed.

[kerbiloid]

7 hours ago, Zeiss Ikon said:

The main reason red is used for lighting in situations like submarine and ship command centers (during emergencies at night), as well as for necessary lighting at astronomy gatherings and so forth, is that deep red has the least effect on the darkness adaptation of the human eye.  Even a fairly bright red light (one that, for instance, allows reading fine print) won't destroy the eye's ability to see in darkness when the red light is turned off or blocked.

That's exactly what I was trying to say.
Red light just gives a soft adaptation for human eyes. In the zoo that's animals' problems whether they can see it too, or not.

Edited January 2, 2018 by kerbiloid

[Chakat Firepaw]

On 12/29/2017 at 9:45 AM, PB666 said:

if its infrared you cannot see it, if its red you can. Its not physics of the universe, its the physics of the eye. To a blind person everything that produces heat is infrared.

I've actually done an intro spec lab where a diffuse reflector was put in place of the cuvette and we had to describe the colour produced.  The prof had a 'what do you mean...' reaction to both me and my lab partner regarding the limits of where we could see red:  "What do you mean you can still see something?" to me, (followed by him fooling with the intensity to confirm that I actually could), and a "what do you mean you can't see anything?" to my partner.

[PB666]

3 minutes ago, Chakat Firepaw said:

I've actually done an intro spec lab where a diffuse reflector was put in place of the cuvette and we had to describe the colour produced.  The prof had a 'what do you mean...' reaction to both me and my lab partner regarding the limits of where we could see red:  "What do you mean you can still see something?" to me, (followed by him fooling with the intensity to confirm that I actually could), and a "what do you mean you can't see anything?" to my partner.

If you are in a pitch black room you will still see something, but then again nothing is there to see.

[Chakat Firepaw]

18 minutes ago, PB666 said:

If you are in a pitch black room you will still see something, but then again nothing is there to see.

Nope, it was in a fully lit chem lab, (although we did shade the opening when looking).