Wikipedia:Reference desk/Archives/Science/2018 March 14

= March 14 =

Elbow skin
Does the skin on human elbows have a special scientific name, and if so what is it? FreeKnowledgeCreator (talk) 02:28, 14 March 2018 (UTC)


 * There is no term for the skin. It is not wenis or wagina, as Google searching will tell you. 71.85.51.150 (talk) 09:57, 14 March 2018 (UTC)
 * If you refer to thickened skin areas these are generally called Callus or in this case simply "elbow callus". --Kharon (talk) 11:59, 14 March 2018 (UTC)
 * You can certainly develop a callus on your elbow - it's possible - but the loose flap of skin there has more to do with the natural loss of elastin and collagen in skin as it ages. As a major joint, the skin gets stretched at the elbow and, with age, it ceases to rebound as it used to. Regardless, I'm pretty sure this question has to do with the "wenis" or "weenis" hoax going around. Matt Deres (talk) 02:57, 15 March 2018 (UTC)
 * Uh, no, not really. I don't follow puerile hoaxes. It was just a question, and Kharon answered it in a satisfactory manner. FreeKnowledgeCreator (talk) 02:03, 17 March 2018 (UTC)
 * If you follow that line, you get a specific answer to the question, as was done by this IP editor:

- 86.152.38.218 15:45, 15 March 2018


 * Lol, I never heard of that before, but there was a character named Wienis in Asimov's Foundation series that I read as a teenager. I remember sniggering over it. 173.228.123.121 (talk) 07:10, 19 March 2018 (UTC)

can any odor be smelled during rain?
If there is a decomposing carcass, can the stink be smelled during a heavy downpour? Thanks. — Preceding unsigned comment added by 49.207.190.13 (talk) 14:29, 14 March 2018 (UTC)
 * Yes of course. Even humans notice the "clean" smell in and after a thunderstorm, which is actually a rise of ozon particles in the air. As you may know many animals have superior Olfaction, some a million times more sensible than human senses. They can even smell unterwater! --Kharon (talk) 17:07, 14 March 2018 (UTC)
 * You probably mean ozone, not "ozon". The smell of ozone is more irritating than pleasant.  As Matt Deres says below, the topic is more fully treated in our article about petrichor, a word that will be familiar to Dr Who fans. --Trovatore (talk) 22:09, 14 March 2018 (UTC)
 * And in case someone invokes the old trope about the smell of "ozone" at the seaside, that smell is actually rotting seaweed. {The poster formerly known as 87.81.230.195} 90.211.131.202 (talk) 21:37, 15 March 2018 (UTC)
 * Ozone Park must've been named by someone misinformed. Sagittarian Milky Way (talk) 20:52, 16 March 2018 (UTC)
 * Recent research indicates that it depends on the specific odor. A 2017 paper in Science titled Poor human olfaction is a 19th-century myth says "When an appropriate range of odors is tested, humans outperform laboratory rodents and dogs in detecting some odors while being less sensitive to other odors. Like other mammals, humans can distinguish among an incredible number of odors and can even follow outdoor scent trails."  CodeTalker (talk) 19:14, 14 March 2018 (UTC)
 * See also petrichor for the general "smell of rain". Matt Deres (talk) 21:08, 14 March 2018 (UTC)

Why do my sunglasses make purple look white?
I got them at a Dollar Store that only charges a dollar for everything, so they're nothing special. [https://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2017_March_8#Why_are_headlights_green? Here] is more about them. A sign at a college near where I live changes every few seconds, and if the words or background look white without the sunglasses, they look purple with them.— Vchimpanzee  •  talk  •  contributions  •  16:24, 14 March 2018 (UTC)
 * You know, the for $1.5 pairs from the gas station make purple look like...purple. You get what you pay for I guess ;)   —SerialNumber  54129 ...speculates 17:18, 14 March 2018 (UTC)


 * I would hypothesize that the sign that changes every few minutes uses something like a light emitting diode that emits in a fairly narrow range of frequencies to produce each of three colors (RGB). Purple is R + B, which are transmitted well by the sunglasses, but the narrow peak of green light might be at the same frequency as a dye in the sunglasses.  Perhaps the maker of the sunglasses, sort of like the maker of the display but in reverse, assumes that if you block out R and G and B in roughly equal amounts, the effect is simply a darkening of what the user sees.  But if there is a narrow-frequency source that happens to match a narrow-frequency absorption, then the output will be very different to the human eye than expected! Wnt (talk) 18:52, 14 March 2018 (UTC)
 * Wnt has nailed it. "Looks white" is no longer any guarantee that some light source is "white", just that it fools eyes into thinking it is. This was an issue for a long time with fluorescent tubes, but with ubiquitous LEDs it's now becoming very obvious.  I'm fitting a paint booth into my workshop and I've just gone back to incandescent lights for it, as the other lighting makes it impossible to correctly [sic] judge paint colours. Andy Dingley (talk) 19:05, 14 March 2018 (UTC)
 * You could do it with graphene.  You could do anything with graphene if you could do anything with graphene...  actually though, I thought there was a trick for converting laser light to "white" light using non-graphene foam, or something, which I'm afraid I've forgotten, and I wonder if there's some other comparable technology. Wnt (talk) 19:16, 14 March 2018 (UTC)
 * It's quite likely that we'll see graphene or other metamaterials replacing existing phosphors in future lighting technologies. Their ability to act as broad-band phosphors gives much more natural lighting, rather than the few narrow spectral lines of RGB LEDs in combination, which are increasingly making any general lighting into an Ishihara plate. Andy Dingley (talk) 20:46, 14 March 2018 (UTC)
 * I wouldn't say the spectra of decent high CRI white LEDs is 'few narrow spectral lines in combination' although it's true they still have peaks. But then again so does much of what people call natural light to some extent. [//www.yujiintl.com/high-cri-led-lighting]   . (I've tried to find decent research articles to include although maybe they aren't always the best. I believe one of the problems is that while there is a lot of research, quite a lot of it is proprietary and not that well published.)  Of course Colour rendering index isn't perfect as we know  (also our article). Still by now, most real developers (I.E. not the cheap Chinese factories trying to tick some box) of high CRI LEDs have moved beyond simply having high CRIs, including ensuring high R9 values one of the common weakpoints and often also high Colour Quality Scale too. Probably other things too, if you're actually in the market for high colour reproduction white LEDs, I suggest you look in more detail. For example, I think TLCI is still generally a separate thing from high CRI if that's something that matters to you. But maybe you can find some which achieve both.  Anyway whatever personal opinions of high colour rendering white LEDs, 'a few narrow spectral lines' seems high questionable. I mean even the classic white LEDs which has clear spectral deficiencies isn't really that, it's still fairly continuous. (See the earlier sources or the later ones.) We aren't talking about ancient fluorescent lights here.  Well unless you count light outside the visible spectrum but the obvious question is why? Efficiency demands suggest to me it's unlikely there will be that much usage of LEDs with significant light outside the visible spectrum except for specialised purposes like grow lights (and these will probably often be intentionally different from natural light). I mean I don't know what 'visible light' is for cats and dogs but I can't help thinking that pet friendly LED lights is always going to be a small market. If you have specific reasons for wanting non visible light, then I guess most LEDs suck for your purposes, but that doesn't mean most people have these demands.  BTW in case these is some confusion, the classic white LED is often only a blue LED with a yellow phosphor generally, Cerium-doped Yttrium aluminium garnet, [//www.sciencedirect.com/science/article/pii/S1875389211004792] . No RGB is involved. Modern high CRI LEDs generally have a more complex phosphor mix but I don't know if it's accurate to call this mix RGB. Probably RYB if you include the original blue component of the LED since I think one of the common things is to add a red phosphor. Some of the even fancier ones possibly add more, but even then I think many still have the yellow, so maybe you'll have RYGB or something. (I'm sure someone can find a R-G phosphor B LED, but I'd like to see some evidence this is a common thing.) You can get RGB LEDs but these are a rarity used for specific applications (LEDs which let you change colours for purposes including colour changing signs like Wnt mentioned) as they cost more and have other disadvantages.  As for graphene or metamaterials, never say never. But I'm far from convinced it's definite. We are getting good at using what we have, so IMO there will need to either be a significant efficiency or performance improment other than pure spectral one, cost or ease of production advantage (which probably ultimately comes down to cost anyway). See for example these comments from a researcher [//engineering.ucsb.edu/news/phosphors-turning-blue-light-white]. Of course it's a promotional story from the university and I don't even know how well recognised the person is in the field, and even if they are reputable they're only one person.  But if we look more widely, while there is interest in different production techniques, including graphene [//www.nature.com/articles/ncomms8767] [//www.seratechnologies.com/what-is-a-graphene-led-bulb/], one of biggest areas of active research seems to be quantum dot LEDs for general illumination (and not just displays)  [//www.osapublishing.org/prj/abstract.cfm?uri=prj-5-2-a1] [//www.led-professional.com/resources-1/articles/quantum-dot-based-white-leds-for-general-illumination] so AFAIK not what are generally called metamaterials (although Graphene quantum dot is one are of interest ). And you'd note in both cases while colour rendering is mentioned, what they concentrate on is efficiency and other such gains.  Actually this is also reflected in the research articles on high CRI white LEDs. One of the big issues is how to add red without adding too much infrared or losing efficiency or luminous efficacy for other reasons. Getting a consistent colour spectra is also desirable since Product binning adds cost etc especially if you end up with too many of the stuff you don't want. (Well there are also other things like lifespan, including consistent colour and CRI over that life, as well as uniformity of light, how temperature affects performance and life, etc. Different technologies may or may not help with these.)  Particularly with the concern of blue light and circadian rhythms, there is increasing interest in tunable CCT and adjusting blue light level, while maintaining a high CRI   (also the earlier one on graphene quantum dot). But even if this does become widespread, however it is achieved, if anything this speaks against an excessively broad spectrum. You don't want one that's only a few lines sure, but you want full one largely only within the visible light range and where you can cut down the blue light when you desire.  Nil Einne (talk) 07:52, 15 March 2018 (UTC)C)
 * Reading Wnt's source, I guess one issue I didn't touch on is the blue peak. This is something which it's true is still not dealt with by phosphor converted blue LEDs. It's probably true there's no easy solution. Proposals have includes phosphor converted violet LEDs instead of blue, but this has concerns including whether violet is actually any better. The other alternative would be to abandon phosphor conversion. I'm not convinced replacing current phosphors with graphene or something else would work, you'd likely need to modify basic operating principles and stop simply converting blue light . For many purposes you could probably simply filter the peak but with an obvious loss of efficiency/luminous efficacy. The obvious question is how much of a concern the blue peak is. Even per my comment above about concerns of blue light and circadian rhythms, as shown in the above sources the blue peak for low CCT high CRI lights tends to be rather small since you don't need much light in the blue part of the spectrum anyway so want to convert most of it. If you want higher CCT lights the blue peak is a bigger issue especially since it means your spectrum tends to be rather limited in part of the blue spectrum, although these aren't very popular in a lot of the West particularly in domestic settings for various reasons anyway. Still use in offices etc means this is an area of active research hence the violet LED proposals etc. Nil Einne (talk) 08:18, 15 March 2018 (UTC)


 * This is a good reason to be careful with very cheap sunglasses. Often they just use coloured plastic or glass to block some wavelengths of visible light. This does nothing about ultraviolet, which is what can damage your eyes, and in fact - because the darker light makes your pupils open wider - they can increase your exposure to dangerous UV. If you can get a UV light source, I'd recommend testing these glasses to make sure they're safe. One easy way to do it is demonstrated here - just shine the UV light through the glasses onto a banknote, and see if the watermark appears. Smurrayinchester 08:37, 15 March 2018 (UTC)
 * "..if the words or background look white without the sunglasses, they look purple with them", this is the exact opposite of what the title is. If the sunglasses make white appear purple I would worry that they are providing no ultraviolet protection at all whilst blocking the middle of the visible spectrum which would be quite bad for you in sunshine as your pupils would be wider with them on. Dmcq (talk) 14:33, 18 March 2018 (UTC)