Talk:Purkinje effect

--hand off--?

What does --hand off-- mean? Surely that's not what it's meant to say. --193.60.223.228 08:20, 14 March 2006 (UTC)

I've changed hand off to transition. Hopefull that's what the author was trying to say. Maybe someone can check it to make sure. THanks for catching that! delldot | talk 17:30, 14 March 2006 (UTC)

Possible contradiction

In my opinion, the paragraph:

Incidentally, the same "lack of sensitivity to red" is why red lights are used in instrumentation panels: the red light does not disrupt the night vision (because the rods do not respond to it), and the fovea is largely L (red-sensitive) cones, hence they are easy to read.

is contradictory, because in scotopic vision (night vision) the rods (and not the cones) are active. So if you want to view a red panel, photopic vision (which is more focused to the fovea) would be more efficient. Of course, if luminance is very low this would not be possible.

In other words, as everyone can experience, night vision is more sensitive to blue colors than red colors (which is what the article says, in fact). So the sentence "hence they are easy to read" seems contradictory.

Possibly, there are other good reasons to use red lights. This one is not convincing to me. 83.58.184.146 19:17, 19 June 2007 (UTC)

I'll attempt to rewrite this section. Red lights are used at a reasonably high brightness level so that the good acuity of the cone system can be taken advantage of. Why not just turn the lights on completely then? Full spectrum light would saturate the rods. Dark adaptation requires about 20 minutes. So, if a crewman on a submarine were reading an instrument panel under full light, and then had to retrieve something from a dimly lit part of the sub, the crewman would be effectively blind for 15 or 20 minutes. By using red lights on the bridge of the sub, the crewman can read the instruments with high acuity without bleaching out the rods - so that he is dark adapted at all times. The eyes can then "take advantage" of the high acuity system and the high sensitivity system simultaneously. SJS1971 (talk) 14:32, 26 November 2007 (UTC)

Blueish?

Since rods cannot make sensation of blue (and any other color) but only of white, I fail to see how the flowers can appear more blueish in the dark. Yes, green and blue parts should appear more bright due to rods, but why more blueish?--MathFacts (talk) 09:27, 14 December 2009 (UTC)

Indeed, I believe you are right. Good thing the article says what it does, and does not say that things look more blue in dim light. Dicklyon (talk) 23:03, 14 December 2009 (UTC)

This is what the article says: Purkinje noticed that his favorite flowers appeared red on a sunny afternoon, while at dawn they looked bluish-red.--MathFacts (talk) 04:46, 15 December 2009 (UTC)

Ah, I see my search missed it due to a difference between your spelling and that in the article. The bit that's quoted says "Green appears more bluish to me"; I think the rest is indeed questionable. Dicklyon (talk) 06:02, 15 December 2009 (UTC)

As always, an example may help. During the daytime, find a collection of objects of different colours. Plastic clothespegs are ideal. Rate the colours in terms of "brightness" (quite a difficult thing to do!). Now look at the same objects in FAINT WHITE light - about the level of full moon (but see note below!). Your perception of which object is "darker" and which is "brighter" is now likely to be quite different to what it was under bright light.

Note that the moon is quite yellowish, and is therefore not an appropriate light source to use in this experiment. In fact the apparent blue tinge that (actually yellow) moonlight gives is in itself an excellent example of this effect. Old_Wombat (talk) 12:49, 25 September 2011 (UTC)

"effect" vs "shift"

Looking at the Jan Evangelista Purkyně article, I noted a link to "Purkinje effect" in the first paragraph under Biography, and another to "Purkinje shift" in the second. Both led to this "Purkinje effect" article, but the "shift" link included a redirect.

So I changed the second link to Purkinje effect|Purkinje shift to bypass the redirect without changing the link's wording. Using What Links Here from the redirect page, I did the same (changed the link destination but not its wording) on three other pages with "Purkinje shift" links. For reference:

• Jan_Evangelista_Purkyně#Biography
• Czech_Republic#Sciences
• Mesopic vision
• Bezold–Brücke shift

Egmonster (talk) 18:22, 24 February 2010 (UTC)

That's what redirects are good for. Why mess with it? Dicklyon (talk) 06:19, 27 February 2010 (UTC)

Is the picture right?

The picture doesn't look like what i would expect based on the description given in the article, is the simulation accurate at all? --TiagoTiago (talk) 23:00, 15 August 2011 (UTC)

No, it doesn't pretend to be accurate, it's just an impression. Maybe you can do a better one. Dicklyon (talk) 00:14, 16 August 2011 (UTC)

I've tried adapting that image from Dicklyon by selectively dropping the red component of the RGB down to zero, while only slightly dipping blue and green (to simulate dropping overall illumination), by adapting the work of Dicklyon. Is this a step forward? Klbrain (talk) 10:19, 21 April 2018 (UTC)

Simulation of mesopic and scotopic visual appearance from a full-color original of a red geranium with greenery and blue in the background, to illustrate the Purkinje effect or Purkinje shift

Hadn't noticed while preparing the image, but while showing the loss of red, it also shows the shift of the white (right side of image) to blue. Klbrain (talk) 10:22, 21 April 2018 (UTC)

Mine included a scotopic (low light level, monochrome) version that you'd get with just rod vision. The mesopic is basically a mix between scotopic and photopic (and I see had misspelled photopic in the my image file name). Just rebalancing the original color channels doesn't get you the intended effect, just a color balance shift. Dicklyon (talk) 15:17, 21 April 2018 (UTC)

A key part of the effect is the change of colour balance we perceive as light levels dim; as the quote from Purkinje describes, in low light levels (above those where we perceive a grayscale) the dominant perceived colour is blue. Specifically, "Blue became noticeable to me first", and "Green appears more bluish to me" and "Nuances of red ... show themselves as darkest for quite a while". My view is that a color balance shift is the key effect being described before the switch to grayscale; the latter is a key part of dark adaptation but not the key feature of the Purkinje effect. I think that the first sentence of the Purkinje effect page correctly describes the key change. While the simulation isn't perfect, simply dropping the red component of the RGB image faster than that of the other channels does seem to be to be reasonable, and does replicate the phenomena described in the article; perhaps also dropping the green component in some intermediate manner might be better, but perhaps just the red is sufficient for the current purpose. Klbrain (talk) 20:29, 21 April 2018 (UTC)

Where he says "Blue became noticeable to me first", he didn't mean it was black at lower light level, but that it was monochromatic, scotopic before that. As the light of approaching dawn arrives, it's often a blueish light, so blue might be the first color visible, and things might look more blueish. But the key is the region where rods still matter and cones start to matter, in which case the Luminous intensity curve is between the scotopic (rod) and photopic (cones) curves; the scotopic curve peaks more in the green and is very low in the red, and the photopic peaks more in the yellow. So even when red starts to look red, it's not very bright or pure red; but it's not greenish or blueish. Dicklyon (talk) 01:17, 22 April 2018 (UTC)

No Sun + blue sky == this effect?

How much of this effect is actually caused by things being more lit by the scattered blue light coming form the sky than by direct white/yellow light from the Sun, instead of by properties of the human eye? --TiagoTiago (talk) 23:04, 15 August 2011 (UTC)

Not much of it, I think, but look it up. Dicklyon (talk) 00:14, 16 August 2011 (UTC)

A very good and highly relevant point. Modern high-performance low-light photoelectronic equipment shows that the night sky is a very similar "colour" blue to the daytime sky, except of course much fainter. So the colour balance of objects under a clear dark sky is more similar to in-shadow-daylight rather than in-sunlight-daylight. Nevertheless, the effect itself exists beyond that, as can be demonstrated using artificial light which is of a known colour spectrum. Old_Wombat (talk) 12:54, 25 September 2011 (UTC)

The blue color of the sky is an interesting idea, but has the Purkinje effect been measured indoors or only outdoors? Cliffswallow-vaulting (talk) 03:42, 21 July 2014 (UTC)

Submarines are not generally dimly lighted.

Submarines are generally well lighted in white light. Manning a sub involves numerous task requiring good visions. Taking logs of various instruments is a good example. This occurs all over the boat. Control is well lighted in white light during daylight hours. Red light is used in control when eyes muct be adjusted to dim conditions if using a periscope. There is no reason the remainder of the sub would need to be kept dimly lighted. There are plenty if good reasons to keep it well lighted.

Audio pronunciation does not match bolded text

The bolded text is "Purkinje phenomenon", the Czech IPA pronunciation is for "Purkinje" only, but the audio file is for "Jan Evangelista Purkyně". Fruascwekexer (talk) 17:55, 25 February 2024 (UTC)