What is yellow? by PehrSall https://www.youtube.com/watch?v=X_1WiWGndZw
PehrSall is a physicist who is interested in the history and science of color theory. He has many video's in which he investigates Newton's and Geothe's color theories experimentally. He also has a video on Land's two color investigations. https://www.youtube.com/watch?v=YG4bzGNc1E0 In this beautiful investigation _Goethe's Purple Ray - alias Monochromatic Rays of Shadow, the Rehabilitation of Darkness_ https://www.youtube.com/watch?v=vu_7uG6KlsU he argues that Newton did not demonstrate that white light consists of variously coloured lights any more than he was able to demonstrate the 'absurd' thesis that darkness consists of variously coloured shadows. (Personally I am not sure that the absurdity of one thesis should be regarded as proof that both theses are unjustified. I am inclined to ask what if the absurd thesis were true?) This paper supports my opinion that there is still much to learn about the nature of radiation. Power Area Density in Inverse Spectra https://arxiv.org/ftp/arxiv/papers/1706/1706.09063.pdf An informal discussion of the results of the same paper in german and english with more pictures: https://www.physikdidaktik.uni-wuppertal.de/fileadmin/physik/didaktik/Forschung/Publikationen/Grebe-Ellis/Mack_und_Goethe_Seite_124-137_freigegeben-low.pd Harry On Sun, Aug 27, 2023 at 2:59 AM MSF <foster...@protonmail.com> wrote: > The delay? I don't think we're in a hurry. And clearly no one else on the > list has an interest in our discussion. > > Spectral colors and their perception are my business. I've made literally > billions of square meters of diffraction gratings, mostly decorative > patterns. Yellow and magenta have been particularly interesting to me for a > few reasons. I am of the controversial opinion that yellow doesn't exist > except in human perception. > > Years ago, before lasers became unbelievably inexpensive, I was interested > in creating a light source to view transmission holograms without a laser > or filtered mercury arc. I had a lot of slide projectors left over from my > "psychedelic light show" so I thought I could use one to make such a light > source. I put a slit into the projector where the slide would normally go > and a high efficiency Bragg diffraction grating in front of it. This > projected a nice broad spectrum. I then used another slit to isolate > whatever color I wanted and a cylinder lens to spread it out. This worked > quite well, but not very bright. I settled on what would normally be called > the yellow part of the spectrum. > > But people viewing the holograms this way would say that the color was > white, or perhaps gray. I thought the same thing. You have to see this to > appreciate it. So maybe Roy G Biv should change his name. Another example > of the phenomenon is a pressure tuned krypton laser. At just the right gas > pressure it makes four more or less equally spaced colors if sent through a > prism: red, yellow, green, and two tightly spaced blues. The yellow looks > yellow when the other colors are present, but by itself it appears to be > colorless. A lot of people smarter than I have argued about these things > for a very long time. > > If you really want to see some strangeness as regards color perception, > look up Land color theory. I played around with this when I was a child, > and my family thought I was nuts. > > I just think it's a gift to us that we can perceive color the way we do. > > ------- Original Message ------- > On Thursday, August 24th, 2023 at 9:10 AM, H L V <hveeder...@gmail.com> > wrote: > > Sorry about the delay. > > I am not sure. If you think about it, overlapping colours don't go along > with the topology of stress lines. > However, cellophane tape is a different situation. It could be that the > perception of the colour magenta is situational like > the perception of yellow. > > > Did you know that a third class of mammalian photoreceptors was > discovered in the 1990's? > Intrinsically photosensitive retinal ganglion cell were only shown to be > definitively present in humans in 2007 in people who were born without rods > and cones. > > From wikipedia " ipRGCs were only definitively detected in humans during > landmark experiments in 2007 on rodless, coneless humans.[15] > <https://en.wikipedia.org/wiki/Photoreceptor_cell#cite_note-ns1-15>[16] > <https://en.wikipedia.org/wiki/Photoreceptor_cell#cite_note-mnt-16> As > had been found in other mammals, the identity of the non-rod non-cone > photoreceptor in humans was found to be a ganglion cell in the inner > retina. The researchers had tracked down patients with rare diseases wiping > out classic rod and cone photoreceptor function but preserving ganglion > cell function.[15] > <https://en.wikipedia.org/wiki/Photoreceptor_cell#cite_note-ns1-15>[16] > <https://en.wikipedia.org/wiki/Photoreceptor_cell#cite_note-mnt-16> > Despite having no rods or cones the patients continued to exhibit circadian > photoentrainment, circadian behavioural patterns, melanopsin suppression, > and pupil reactions, with peak spectral sensitivities to environmental and > experimental light matching that for the melanopsin photopigment. Their > brains could also associate vision with light of this frequency." > > Harry > > >
