Timeline for What actually is white light?
Current License: CC BY-SA 4.0
22 events
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| Mar 28, 2021 at 2:43 | comment | added | Mark Ransom | @PhysicsTeacher the concept you're talking about is called Metamerism. Light bulb makers have a measurement called CRI that attempts to quantify the effect, but it's not perfect. I insist on using incandescent bulbs to illuminate product pictures because they generate true white light, even though they're getting harder and harder to find. | |
| Jan 10, 2021 at 5:13 | history | edited | anna v | CC BY-SA 4.0 |
edited in a comment
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| Jan 9, 2021 at 20:18 | comment | added | PhysicsTeacher | Excellent answer, but it should be noted that when speaking generally of "white light" one often means light that contains all the spectrum to a significant degree, rather than just a combination of a few frequencies. This is because the context is often that of illumination, and illumination with a weird and tiny frequency combination will result in distorted, "artificial" colors ratther than the "real" colors (i.e. the colors seen in daylight). | |
| Jan 9, 2021 at 15:20 | comment | added | anna v | it is correct only at the center of mass rest vrame of a massive particle.zero mass particles do not have a rest frame as they always move with velocity c. . A particle moving with velocity close to the velocity of light displays an inertial mass according to $E-mc^2$ , a relativistic mass which is a function of velocity, so is no longer in use in studying particles. Ist only real use would be for spaceships traveling close to the velocity of light to see how much extra fuel they would need to go faster. | |
| Jan 9, 2021 at 14:18 | comment | added | user279395 | So this equation:E=m*c^2, it is incorrect, as photons do not conform to it? | |
| Jan 9, 2021 at 14:08 | comment | added | anna v | @XeнεiΞэnвϵς You are not correct in your opinions , main stream physics photons have zero mass and obey four vector algebra , their energy equal to momentum in the frame c=1 hyperphysics.phy-astr.gsu.edu/hbase/Relativ/vec4.html . | |
| Jan 9, 2021 at 13:22 | comment | added | user279395 | I have to disagree with you, you say photons do not have mass, it is only true if photons were static, it is true they don't have rest mass, but there are not static photons; Photons do have energy, and according to relativity, energy is mass so mass of photons is E/c^2 and hf/c^2 however small it is... | |
| Jan 9, 2021 at 7:28 | comment | added | anna v | @Vorbis please see my edit, for the white region two lines are enough, which I understood rereading the link. The T is for the chromatic regions, the E is the center of the achromatic region | |
| Jan 9, 2021 at 7:25 | comment | added | anna v | @MarkRansom not to worry, we agree :). I had received a negative vote overnight (just woke up) and I thought your comment was related in my mistaken, before edit, statement that as with the T point in the colored sections white would also need three lines, then I reread the link and saw that two would be enough for the achromatic (white) region. | |
| Jan 9, 2021 at 6:05 | comment | added | Mark Ransom | Sorry if my comment sounded like a criticism, it wasn't - rather it was meant to bolster your point. There are infinite combinations of wavelengths that look like "white" to us, and the diagrams we use to interpret color can sometimes obscure that fact. | |
| Jan 9, 2021 at 5:45 | comment | added | anna v | @MarkRansom I finally think that is what the plot shows for white light that is why I edited last.time. the triplets are a matter of illustration. | |
| Jan 9, 2021 at 5:37 | comment | added | Mark Ransom | A key point is that there are many ways of arriving at white. Most white LEDs combine a blue LED with a yellow phosphor, so you don't even need all 3 RGB primaries. | |
| Jan 8, 2021 at 19:32 | history | edited | anna v | CC BY-SA 4.0 |
clarification
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| Jan 8, 2021 at 16:31 | comment | added | SiHa | I'd upvote this twice if I could, It's really helped my understanding of photons and colour perception. Given that I work in the field of video encoding, the last is quite important! | |
| Jan 8, 2021 at 15:54 | comment | added | anna v | @Ruslan if you read the link I gave last, it is still under research if one photon can excite enough the cones to give a flash let alone a color perception.,The link you give speaks of "flashes of light", light is hundreds of thousands of photons. | |
| Jan 8, 2021 at 15:16 | comment | added | Vorbis | @anna v, in your comment of the figure you say that "The combination of three pairs as described in the figure, gives the perception of white". Unless I'm missing something, these three pairs give the perception of color T, which is not white but light green... | |
| Jan 8, 2021 at 14:31 | comment | added | fool4jesus | Thank you for this really good answer. Until now, I've never understood that color perception diagram. | |
| Jan 8, 2021 at 14:16 | comment | added | Ruslan | "A single photon cannot give the perception of white." — this is not quite true. Some of the cone cells (in fact, more than half of the population) in the retina generate achromatic percepts, despite having the usual spectral sensitivity, see e.g. this paper. | |
| Jan 8, 2021 at 14:07 | comment | added | Ruslan | @Michael in fact, all colors that you can actually see are real. But there does exist the concept of "unreal" colors — impossible colors. | |
| Jan 8, 2021 at 6:36 | comment | added | Michael | Your answer made me realize that all the fuss about pink not being a real (spectral) color is (should be) overshadowed by the fact that white isn't either! | |
| Jan 8, 2021 at 5:48 | history | edited | anna v | CC BY-SA 4.0 |
clarification after comment in new answer.
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| Jan 7, 2021 at 16:18 | history | answered | anna v | CC BY-SA 4.0 |