Wikipedia:Reference desk/Archives/Science/2021 August 20

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August 20

Flashlights question.

Is the high-medium-low for flashlights only for incandescent light? When I was a kid in the 1990s, we had a chandelier that was sliding-switch, meaning as you slide up or down, the bulbs all got brighter or dimmer together. Is this not possible with LED lights? Why can't LED flashlights have a high-medium-low buttons? We know this could be done with batteries in parallel, by temporarily cutting 1 off, but can this be done via batteries in a series? Also, LED flashlights with multi-brightness, tend to be either you turn it completely off, turn it on, and it's dim, then turn it off, then turn it back on and it's bright, and repeats (so only 1 button you keep on pressing). Or, other flashlights that have multi-level brightness, dim = where only 1 bulb is at full capacity, and bright = where all bulbs are at capacity, rather than dimming all bulbs gradually. So, is it just not feasible to make LED flashlights with dimmer/brighter options, as in high-medium-low or just sliding brightness? Thanks. 67.165.185.178 (talk) 03:05, 20 August 2021 (UTC).

There are tons of dimmable LED flashlights. www.fenix-store.com has lots of nice ones. Dimming is easier with LED's because the color doesn't shift as much. Dimming is usually done with pulse width modulation but some of the nicer lights will instead decrease the current to the LED (this is a little bit more difficult) so there is no flicker. 2601:648:8202:350:0:0:0:2B99 (talk) 04:26, 20 August 2021 (UTC)

Unless you want candlelight dinner atmosphere then a 25 watt incandescent in a dimmer could do. Sagittarian Milky Way (talk) 05:15, 20 August 2021 (UTC)

How do you decrease the current from a battery, does it also change the resistance or voltage, or do those remain constant? 67.165.185.178 (talk) 11:33, 20 August 2021 (UTC).

• Our article dimmer might be of interest. I have at home a sliding-switch lamp with an LED fixture. The LED has not broken in ~2years of use so the setup must not be outrageously bad. I do not know whether I could use a halogen lamp with the same dimmer.

I must say that I am quite surprised to read in LED circuit that The voltage drop across an LED is approximately constant over a wide range of operating current; therefore, a small increase in applied voltage greatly increases the current. I have a vivid lab memory of controlling the current through a high-power LED directly by the knob of a Switched-mode power supply (possibly it was an intensity knob rather than a voltage knob?). Tigraan^{Click here for my talk page ("private" contact)} 08:53, 20 August 2021 (UTC)

Checking if the corona vaccine worked

Is there some procedure that can verify that the Janssen COVID-19 vaccine has produced enough antibodies? If no, which other covid vaccines can be tested in that way? 31.217.37.79 (talk) 09:51, 20 August 2021 (UTC)

• Measuring the concentration of antibodies is certainly a standard procedure, and what many studies do when investigating how the immunity system reacts to a vaccine (example). This applies to all vaccines (covid-targeted or not).

Whether a given level of antibodies is "enough" is of course a much more complicated issue. It might depend on patient-specific characteristics, on the specific strain of virus, it might protect against symptoms but not against asymptomatic infection, etc. The reason antibody dosing studies are commonplace is that it is easy to do (administer vaccine, wait X amount of time, take a blood sample, do the dosing). Estimating the vaccine efficiency (i.e. by how much taking the vaccine reduce the chance of infection) requires to split patients into treatment and control groups (which is a long process), wait until enough of them are infected (which can take a long time) (or expose them deliberately, which is highly unethical for a virus as vicious as the covid19 strands), and do complicated stats. Tigraan^{Click here for my talk page ("private" contact)} 11:52, 20 August 2021 (UTC)

• This is one of those things that data is statistical and not individualized. Measuring the effectiveness of a vaccine is done through controlled studies of statistical significance. We can tell over large populations that the vaccine is effective in preventing disease in that population, what we can't say is that the vaccine will be effective in absolutely stopping disease in YOU. This kind of statistics is usually most effective when looked at as Bayesian statistics, a mathematically rigorous way to use data to update our levels of certainty in the likelyhood of certain events. The issue is that there is not a simple chain of events that will lead to you being infected or not. Let's say you get the vaccine, you have an antibody test, and you find that your antibodies are at some level. Let's also say that you never get infected. Perhaps you didn't get infected because the vaccine did its job. Perhaps you didn't get infected because you have never been exposed. Perhaps you didn't get infected because your immune system would have fought off the infection effectively even without the vaccine. For YOU we could never answer that question. For a sufficiently large group of people we can. --Jayron32 12:22, 20 August 2021 (UTC)

Of course you can, it's a simple matter of paying $70 for an antibody test from Quest Diagnostics. Abductive (reasoning) 14:05, 20 August 2021 (UTC)

That just tells you that you have the antibodies in your system. That doesn't tell you that because you have those particular levels of antibodies, that you either will never get the disease, or that those antibodies are the reason you didn't get the disease. Maybe it is, it might even be likely that it is, but there's no way to determine with certainty that it is in your case. --Jayron32 14:07, 20 August 2021 (UTC)

If you have the antibodies at the level they consider "positive" you are protected. If the virus reenters your body, and gets taken in by a cell, it will begin replicating, and you now have been infected. This happens every time, no matter what the level of antibodies you have in your system. So everybody is 100% likely to be reinfected eventually. Next, the immune system responds. Since you have antibodies, it means that your immune system responded properly to the vaccine or previous infection, so unless something has changed, your body will successfully fight off the infection. Abductive (reasoning) 20:46, 20 August 2021 (UTC)

Your body will do its best to successfully fight off the infection. Due to fever, inflammation, drowsiness and a wide range of relatively uncommon autoimmune reactions, disorders and deficiencies, your body might kill everyone and everything inside it before the COVID can. Which is victory, but for most people, Pyrrhic victory is hardly considered success. InedibleHulk (talk) 09:33, 23 August 2021 (UTC)

• A bit of nuance would not hurt, would it? There are many vaccines for many diseases that work in many different ways, with widely varying vaccination schedules. For instance, the flu vaccine is an annual shot with an efficiency around 50% (because the flu mutates quite a lot so it is developed on-the-fly to target the next winter season); measles is a one or two shot with near-100% efficiency. And that is only about variations of the pathogen. The vaccination schedule is all over the place, too, depending on what age the shot(s) are most efficient.

It might be that covid vaccines (which one by the way?) provide stable long-term immunity. There will be some studies that show or disprove it in the near future. The best we could do right now is informed speculation, such as looking at MERS/SRAS immunity longevity studies and assuming covid19 and its vaccines behaves similarly. Tigraan^{Click here for my talk page ("private" contact)} 11:55, 23 August 2021 (UTC)

In general, vaccines almost always involved booster shots. J&J made a partly commercial decision to position their vaccine as a one-time shot. Studies show that a booster shot, especially of the mRNA variety, significantly increases protection. Side effects are increased over either type of vaccines alone, however. Imagine Reason (talk) 18:41, 20 August 2021 (UTC)

Please give a reference for Studies show that a booster shot, especially of the mRNA variety, significantly increases protection. There are studies to show that a booster shot increases antibody levels after one month or so (because that is the easy thing to measure). One might speculate that it results in an increase in vaccine efficiency (i.e. by how much the rate of infection is cut), but unless someone has run a real trial it is impossible to know how much it raises the VE (if at all). Tigraan^{Click here for my talk page ("private" contact)} 11:55, 23 August 2021 (UTC)

I was thinking of an AstraZeneca study in Germany or the UK, where the initial shot is almost always a viral vector. One may extrapolate the result to the Janssen shot, but I should've noted the distinction. I'm afraid I don't have the link on hand. 161.185.160.175 (talk) 18:24, 23 August 2021 (UTC)

Are the CDC and FDA suddenly so incompetent or are they only recently scrutinized?

The FDA has granted authorization to a dangerous Alzheimer's drug and one for narcolepsy, not to mention hyping up COVID-19 remedies. CDC told people to drop their masks and that's contributed to the spread of the Delta variant, and both agencies look set to push third boosters even as they claim that the vaccines still protect against severe symptoms.

The pandemic is endemic and we should be using multiple forms of protection. We should tell people that even the vaccinated are spreading, sometimes superspreading (per contact tracing in Singapore, Boston, and California), the virus. Why is the CDC so mask hesitant even when their own scientists are calling for universal masking? Imagine Reason (talk) 18:49, 20 August 2021 (UTC)

There are a number of articles in the media saying that the CDC and FDA were hollowed out by neoliberal politicians over the years. Abductive (reasoning) 20:48, 20 August 2021 (UTC)

As is argued in this article, for years neoliberal policies have weakened the health sector in general. This can hardly explain the surprising FDA approval of aducanumab, though. Since both experts and "the media" appear puzzled, we can't do more than offer speculations, for which the reference desk is not an appropriate forum. As to curbing the spreading of COVID-19 (basically, to get the reproduction number down), it is not hard science how (in)effective different measures (other than vaccination) are. It is not practically possible to conduct large-scale controlled trials that cover all relevant settings; the data can for the most part only be collected through haphazard and uncontrolled experience and so is disorganized, very incomplete, and often low-quality.  --Lambiam 07:16, 21 August 2021 (UTC)

Is it "conservatives" who are making that argument? ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:20, 21 August 2021 (UTC)

Who are you quoting in asking that question? --OuroborosCobra (talk) 16:42, 21 August 2021 (UTC)

Self-styled "conservatives" who lack truly conservative values (which is most of them). ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:43, 21 August 2021 (UTC)

Which argument? That it is not practically possible to conduct large-scale controlled trials that cover all relevant settings?  --Lambiam 08:39, 22 August 2021 (UTC)

No, that liberals are somehow responsible for deficiencies in the healthcare system. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:56, 22 August 2021 (UTC)

Neoliberalism isn't liberals. Abductive (reasoning) 06:58, 23 August 2021 (UTC)

I largely agree with your response. I'd like to point out, though, that the CDC went from recommending double-masking to telling the vaccinated to drop their masks to telling people in high-prevalence areas, whatever that means, to wear masks indoors, all within a few months, really takes away their credibility. This isn't January 2020. 161.185.160.175 (talk) 18:32, 23 August 2021 (UTC)

So, here's the thing that you don't seem to realize: That the body of knowledge around Covid-19 is not something that has existed since creation, and that the CDC isn't being arbitrary in their recommendations. New data is coming in all the time, and the situation is changing all the time. The CDC recommendations are based on the available data of what the situation is at that time. They change their recommendations based on the exact situation at that time. I would be far more worried if the CDC looked at new information and said "Look, we know things are different than they were a while ago, but we're not going to change our recommendations because we made them once, and darn it, we're just going to have to stick with those forever". I expect, and am encouraged, by an organization that is responsive to changing situations and willing to be adaptable. An adaptable organization is far more trustworthy than one that ignores new information and stubbornly stands by past decisions for no reason other than that they made them already. --Jayron32 12:34, 25 August 2021 (UTC)