Wikipedia:Reference desk/Archives/Science/2020 July 13

= July 13 =

Person claims to sleep just a few hours a week
Is that even slightly believable? Thanks. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 06:52, 13 July 2020 (UTC)
 * Not without a better source than a random forum post. Per our article, self-reported sleep duration is only moderately correlated with actual sleep time as measured by actigraphy, and those affected with sleep state misperception may typically report having slept only four hours despite having slept a full eight hours. (I know the random forum post claims to have evidence that they were actually awake and functioning, but the post also ends with "now I found a way to actually sleep and my life is much better" which makes me extremely suspicious of all the previous claims - if they did need that presumably the actual doctors that examined them would have suggested something of the sort.)
 * A cursory search on Google Scholar reveals multiple studies showing a positive correlation between sleeping less than ~7h/day and various health risks, but this does not answer the question of whether some humans (even a small fraction of the general population that would not appear in average stats) can sleep less than an amount X per day and still be functional. Tigraan Click here to contact me 12:22, 13 July 2020 (UTC)
 * There are some genetic conditions which result in a normal sleep length of 6 hours and this paper implies that sleep needs tend to be overestimated as most methods to trigger sleep deprivation also trigger stress which acts as a confounding factor. Jo-Jo Eumerus (talk) 12:28, 13 July 2020 (UTC)


 * Unless someone has Fatal familial insomnia, Mother Nature usually wins the sleep deprivation battle. ←Baseball Bugs What's up, Doc? carrots→ 16:14, 13 July 2020 (UTC)
 * Well all I have to say to that is...is...Zzzzzzzzzzzzzzzzzzzzzzz.... --Guy Macon (talk) 19:28, 13 July 2020 (UTC)
 * Being in STEM grad-school or being a new parent are generally considered good pools of data for minimal sleep for days on end. DMacks (talk) 19:39, 13 July 2020 (UTC)

How many Lumens?
While looking for a good headlamp for my night runs, I came across a large amount of lamps in AliExpress and in Amazon, claiming to emit as much as 8000, 10000 and even 12000 Lm. On the other hand, some highly recommended headlamps like this one declare a light output of 450 Lm. What is going on? Gil_mo (talk) 21:46, 13 July 2020 (UTC)
 * A clear 100 watt incandescent tops out in the 1800 lumen area and needs 120 volts and 0.83333 amps. 2020 LEDs would need not much less (volts multiplied by amps) to produce 12 kilolumen. Did you know early 21st century New York City streetlights on middle class streets with 1 resident per 4 or 5 inches of streetfront were usually only 150 watts? And many times brighter than a 150 watt incandescent? The amount of lumens they're claiming here is almost that bright. Sagittarian Milky Way (talk) 01:32, 14 July 2020 (UTC)
 * The concept of a 10000 lumen headlamp is ridiculous and the 450 lumen one would probably heat up uncomfortably if you kept it on high power for a long time while running. If you got it and used it in a low (100 lumen) setting it will likely be fine.  LEDs are fantastically more efficient than incandescents though.  And old fashioned two cell flashlight (KPR2 krypton bulb) may have made 20 or 30 lumens.  A car headlamp makes around 500 lumens.  You probably don't want a super bright headlamp for running since it will mess up your night vision.  You just want to see where you're going and not run into stuff.  Use the low setting and have the high available if you want to light up something in the distance.  The very best LED's today make around 200 lumens per watt of electrical power so you can figure out what a 10000 lumen light would do to batteries.  They might have meant 10000 candlepower which is fairly meaningless since you can get it arbitrarily high by focusing the beam to a tiny spot. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 05:20, 14 July 2020 (UTC)
 * A further consideration might be how much one wants to dazzle any pedestrians and motorists whom one is approaching. I have sometimes had to stop my car because an oncoming cyclist on the opposite side of the road and a considerable distance away had an LED headlight so bright (and so mis-aligned) that I could not see anything at all in front of me. {The poster formerly known as 87.81.230.195} 90.200.41.197 (talk) 08:30, 14 July 2020 (UTC)
 * I would like to second this, this is an everyday problem for me (a cyclist - doesn't just apply to pedestrians and motorists!) in winter. Your light - whichever you end up getting) needs to be aimed mostly downwards at the road some distance in front of you, or it will be a safety hazard. Fgf10 (talk) 09:23, 14 July 2020 (UTC)
 * (OP) So, it seems that the 10000 lumens advertised would light up a stadium, right? To be blunt, are they lying, all hundreds of sellers? Gil_mo (talk) 09:25, 14 July 2020 (UTC)

Electrical engineer here.

Here is a 1500W LED Stadium Flood Light that puts out 225,000 lumens: (Click on the specifications link.), It costs $4,579.00. They make a 12V model so you can you can mount a pair of them on your monster truck (assuming that you have 250 amps at 12V available...)

You can buy a single LED that puts out 2,000 Lumens It will cost you around $10 and you will need to hire a good engineer to design the driver circuitry and the heat sink. We are way past "put a resistor in series" territory here.

--Guy Macon (talk) 13:33, 14 July 2020 (UTC)


 * (OP) My question again: are they lying, all hundreds of sellers? Gil_mo (talk) 14:16, 14 July 2020 (UTC)


 * Does it have a single LED? Does it have a Lumen figure much larger than 2000? If so they are lying bastards. Nobody make an LED that puts out much more than 2000 Lumens. Four LEDs? 8000 Lumens max. (Make sure you aren't accidentally looking a HID, which puts out more from a single lamp than an LED.) Buy from a reputable vendor such as Diode Dynamics, and you won't get lied to. Hundreds of lying sellers is nothing new. Most of the time they are a handful of lying sellers with hundreds of identities.
 * Do take a look in AliExpress by searching for "head lamp LED". You'll even find a 300000 Lm piece. Gil_mo (talk) 15:12, 14 July 2020 (UTC)
 * Why would anyone even want the light of 200 frosted hundred watt incandescents or like literally 20 fairly bright streetlights in a headlamp? Sagittarian Milky Way (talk) 16:44, 14 July 2020 (UTC)
 * Someone who wants the police to impound their car as being a hazard on the road? A little too bright and you get a ticket. Way too bright and the take away your car and leave you standing alone on the street. Hope you remembered to charge that cell phone!
 * There is a place for brighter lights, and that's when you are in a specialized vehicle traveling off road, or an emergency vehicle that has stopped and is illuminating an accident or crime scene. But even they don't use bright headlamps; wrong pattern. They use things like this: [ https://www.diodedynamics.com/stage-series-42-white-light-bar.html ]. In California you have to cover the off-road lights with an opaque cover when driving on the road. I have never seen a light bar sold in California that didn't have a cover in the box; perhaps that is a legal requirement to sell in California? --Guy Macon (talk)


 * You may be interested in my new invention, the Dark Emitting Diode, or DED. These are commonly referred to as "Dead LED's", and are built on the technology used in my my inoperational amplifier, write-only-memory, and TTL Never gates. I even have a procedure for turning any LED into a DED, and a white paper for creating your very own single-shot smoke emitting diode out of any standard diode. --Guy Macon (talk) 14:51, 14 July 2020 (UTC)
 * Sell me 1000 DEDs so I could darken my room :)
 * Sellers are playing on the fact that 99% of people buying a headlamp won't have a clue what a lumen looks like. All they want is the best brightness for their bucks, so they click on the biggest number. As long as they're happy with the product they won't want the bother of returning it.--Shantavira|feed me 09:56, 15 July 2020 (UTC)