Not Electronics but "Optics" related question - Page 1
Forum section: electronics / general

author: sainbablo
author_rank: Regular Contributor
timestamp: October 23, 2016, 04:45:12 pm
content: White light after passing through a prism breaks up in V I B G Y O R color spectrum.My question is if I mix equal quantities of liquid paints of above mentioned colors wouldthe resultant mixture be "White" ? Thanks for your interest.

author: helius
author_rank: Super Contributor
timestamp: October 23, 2016, 04:52:36 pm
content: The mixture will be a dull brown color.Additive and subtractive color are different concepts, seehttps://www.willamette.edu/~gorr/classes/GeneralGraphics/Color/add_sub.htm

author: sainbablo
author_rank: Regular Contributor
timestamp: October 23, 2016, 05:12:46 pm
content: Hi, heliusI have been to the site you mentioned. The source of colors is froma color monitor and green, blue and red colors are in the example.Can this explanation be valid in the example of VIBGYOR radiant vibrations emanation from a prism?

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2016, 05:19:00 pm
content: Quote from: sainbablo on October 23, 2016, 04:45:12 pmNo, but if you paint a disc with a sector for each color and spin the painted disk fast enough, then you will see it white.

author: ez24
author_rank: Super Contributor
timestamp: October 23, 2016, 05:27:59 pm
content: My experience with mixing lots of paint is it always ends up a shade of brown

author: sainbablo
author_rank: Regular Contributor
timestamp: October 23, 2016, 05:34:00 pm
content: No, but if you paint a disc with a sector for each color and spin the painted disk fast enough, then you will see it white.Hi RoGeorgeIt is a logical answer. What about thethe radiant component of the original vibratory energy?

author: RoGeorge
author_rank: Super Contributor
timestamp: October 23, 2016, 05:43:32 pm
content: Sorry, I have no clue about that.

author: SeanB
author_rank: Super Contributor
timestamp: October 23, 2016, 06:09:03 pm
content: Each segment of the disk absorbs all other radiation 9 within limits) and reflects a portion, which you see as a colour. Spinning the disk means the eye is exposed to a sequence of colours, and the eye and brain integrate this ( the eye and brain have a relatively slow response rate, so any series of colours that reach a particular point of the retina within the integration time of the eye, around one 20th of a second, are seen as if they were a single source made from that colour) into a white disk, though the reflected light is appreciably lower in intensity as most of it has been absorbed by the pigments.You cam also make a white light by mixing the light from a few LED's, so mixing a blue, green and red led through some optics to blend them into a point source will appear to be a white light. This is how the large LED signs make a colour image, and how white leds work ( though there it is a blue light source, with a phosphor blend that makes a green component from the blue and another that produces red, with some more expensive ones having extra to make a better quality of light from the original blue) and how an OLED display makes white and other colours.

author: helius
author_rank: Super Contributor
timestamp: October 23, 2016, 06:14:39 pm
content: Quote from: sainbablo on October 23, 2016, 05:12:46 pmA prism is just a refracting device, it has no preferences to absorb or emit light at any wavelength. Refraction makes the colors bend at different angles: this is a property of all simple lenses.If you put a prism in front of a computer monitor showing White, it will spread into Red, Green, and Blue bands, with no other colors, because those are the only wavelengths emitted from the screen. Because human vision is trichromatic, those are the only ones you need to reproduce color sensations.

author: sainbablo
author_rank: Regular Contributor
timestamp: October 23, 2016, 06:31:36 pm
content: Please allow me to expand the topic.On one hand of the visible spectrum we have beginning of ionizing radiations. On theother side we have beginning of larger infrared radiationsThe white light has heating effect when beam is narrowed after passing through convex lensconverging at its focal length.Where as same white beam breaks up into its component V I B G Y O R after passing througha prism. None of the emerging individual color vibration carry heat energy to its original level.As the contributors have opined rotating a proportionately colored disc at a speed where retinal afterimages lap upon each other in succession giving (cerebral) visual cortex impression of "white" light is a fairconclusion.But the thermal component is lost. It can not be reproduced by disc example.My question is why semblance of heat sensation is not produced when visual cortex perceives white color throughrotatory disc example?

author: helius
author_rank: Super Contributor
timestamp: October 23, 2016, 07:02:33 pm
content: The thermal "sensation" is produced by heat-sensitive peripheral nerves. They are present in high quantities in the extremities like the hands and face, but not in the eyes themselves, which is why infrared light is so dangerous to look into. The sensation is caused by heating, whether it is by conduction, convection, or radiation doesn't matter. You could make the analogy that we sense heat like a microbolometer, not like a direct-bandgap IR detector.The heat content of all wavelengths of radiation is according to the Planck equation, and infrared light is not special in any regard other than being 1. invisible, and 2. near the peak of the blackbody curve for objects in the terrestrial temperature range. Objects on Earth rarely reach thousands of °C, where their emissions would be primarily visible. Please note that the visible radiation from a 5000°C object is no cooler than the infrared emission from a 800°C object!Whether a visible light can be focused to produce sensible heat depends on its brightness, that is, its radiant intensity. Light from the Sun is very bright (as a consequence of the surface's high temperature) and it is easy to feel heat from it. To detect heat from cooler objects, the sensor must be cooled first below the temperature of the target, or else a thermal equilibrium would exist.

author: sainbablo
author_rank: Regular Contributor
timestamp: October 24, 2016, 05:21:07 pm
content: Hi " helius" Thanks for your inputIn fact my question was badly worded.Like must be compared with like otherwise inferencewill be illogicalBy comparing a natural phenomenon like light and its defraction after passing through a prismcannot be compared by its restitution by disc example which in fact rests on the ability of human eyeto integrate the images of the colored disc components which is time dependent activity (ie before decay of previous image occurs,the succeeding image stimulates the retinal receptors), of impulses from rods and cones on wardsto visual cortex. Slowing down of the disc below the critical speed will render individual colors to reappear and nullify theexperiment.Therefore in this example perception of only "whiteness" is created.But then, here is another question, would not the psycho visual cortex impart a general feeling of "warmth" withinconsciousness of the observer?

author: helius
author_rank: Super Contributor
timestamp: October 24, 2016, 08:51:06 pm
content: Do you mean "warmth" in some particular way that isn't clear to me? Artists call certain colors "warm" or "cool", because they have respectively more red or blue in them, which affects the feeling. If you draw with warm gray against cool gray, the warm tone will seem to be moving towards you, and the cool tone will seem to be moving away.I was using the more standard meaning of warmth as "sensible heat". If you meant something visual, that would be different. But there is a certain influence of suggestion on the perception of heat, to the extent that visualizing a very warm place can reduce the feeling of cold, and vice versa; in a very similar way, visualizing running water will make it more difficult to hold in micturition. These effects are probably processed through the sympathetic nervous system.In any case, the standard explanations of color vision are not wholly satisfactory, as the full spectrum of hues can be experienced when only two nearby wavelengths are actually present. It is much more complicated than we have been led to believe.

author: ar__systems
author_rank: Frequent Contributor
timestamp: October 25, 2016, 12:11:56 am
content: Quote from: RoGeorge on October 23, 2016, 05:19:00 pmNo. If you paint a disc white and spin it you will see it white. If you paint a disc with spectrum colors, you will see it as dark grey.

author: sainbablo
author_rank: Regular Contributor
timestamp: October 26, 2016, 08:48:53 am
content: To "helius"I mean "warmth" in subjective way. A kin to Dejavue phenomenon. I agree with you that at this point discussionwould digresses into considerations of connexions of visual cortex of cerebrum with deeper structures of brain and onwards tothe autonomic component as well as associated visual memory stored experience ( including properties like warmth) about this particular signal "white light" Discussion along this line might not be profitable.But if I may, by analogy, attract your attention to auditory component of CNS, and put forth an example of a visual imageof cars about to collide but in fact fail to do so, causing onlooker to wince, as a reflex protective action, in anticipation ofloud bang or may be fear, (it is recorded that the ear drum becomes relatively stiff as a protection against likely anticipation of loud bangto forestall damaging the inner structures).But then one can always turn around and say that the later example(auditory) does not match the first one that is the visual one.There is merit in that argument.No denying.What I am wondering wether perception of artificially created white visual impulse would trigger the recall to consciousness of otherassociated properties of original impuse, not in way of creating sensation of warmth within body but imparting, momentarely, a fleetingfeeling of warmth how so ever it may be unreal.Thank you

author: helius
author_rank: Super Contributor
timestamp: October 26, 2016, 03:28:28 pm
content: That's an interesting question I have no good answer to. But I suspect it has something to do withCRIand the subjective appearance of objects reflecting the light. Because of color constancy, colors appear the same in sunlight and in shade, but low CRI lighting makes them look less lifelike. There arevery bright light sourcesthat possibly may induce a similar feeling to sunlight (including being too bright to look at directly).

author: sainbablo
author_rank: Regular Contributor
timestamp: October 26, 2016, 03:59:29 pm
content: Hi "helius"My profound thanks to you for enabling me to visit the CRI site.I am humbled by the quantum of knowledge displayed therein.First few lines indicate that my answer may lie there. But it will require time to absorb it.And good eye sight too.Time to sum up the discussion for the time being, with lots of thanks to knowledgeable individualswhose presence makes visiting eevblog a worth while an experience.Best Regards