Hot answers tagged

53

YES, it is possible to project images onto clouds, and it has been for quite some time. A Sky Projector from 1931: From Fortean Times: By the late 1920s, Harry Grindell Matthews was back in Britain with a series of new, bold inventions which actually worked. His piece de resistance was a device to project advertisements on clouds. On ...


26

A very simplistic calculation shows that the initial energy input is quickly paid back. The cited numbers show a manufacturing energy difference of 1.8 - .11 = 1.69 kW-hr = 1690 W-hrs. A CFL with a light output equivalent to a 75 W incandescent bulb typically uses about 20 W, or about 50 W less than the incandescent. 1690 w-hrs divided by 50 watts = 34 hours....


24

The expectation you're asking about is called Emission theory: obeying the usual laws of Newtonian mechanics, and we expect light to be moving towards us with a speed that is offset by the speed of the distant emitter (c ± v). If you look at the section entitled Refutations of emission theory, you'll see some of the most concrete examples of how this was ...


22

According to the OSHA manual on preventing strain from working with video display terminals, three elements are of concern when it comes to lighting: quantity (lower lighting is better, OSHA recommends “28-50 foot candles”) contrast (lower produces less strain) glare (again, lower or more diffuse light is better) See: http://www.osha.gov/Publications/...


21

An analogy: suppose there's a long line of swings. You run along the line, pushing each swing as you go. This will result in each swing being slightly out of phase with the one before it. There will be appear to be a "wave" traveling down the line of swings at the same speed that you ran down it. For instance, if you look for a swing that at its maximum ...


13

A typical blue light therapy product such as the Philips goLITE is advertised as having the wavelength 460-485 nm, with an indicated peak wavelength of 468 nm ± 8 nm. While even exposure to normal daylight [1] increases the risk of such degeneration, blue light [2] is most likely to do this. Lipofuscin [2] and chronic inflammation [3] play roles. As far as I ...


12

Well there were experiments that confirmed it, some in a straightforward way. Most notable was Michelson--Morley experiment. When Einstein said that speed of light is absolute he really simplified view of the universe. Basically to state the opposite we must say that there is some magical base reference and that all measurements of speed of light are done ...


11

Yes, it is recognised as a potential problem: LED lighting flicker and potential health concerns: IEEE standard PAR1789 update. The IEEE Standards Working Group, IEEE PAR1789 “Recommending practices for modulating current in High Brightness LEDs for mitigating health risks to viewers” has been formed to advise the lighting industry, ANSI/NEMA, IEC, ...


11

Q Does switching the lights off help avoiding mosquitoes? In short: "yes", but with so much caveats that ultimately the needed qualifier is "but it's not effective". The caveats are: not all species at all stages of life-cycle. Even within the same species some inconsistent behaviours regarding light seeking or avoidance have been described. Some are ...


10

The thinking is that disrupted sleep results in lower melatonin production which through some unknown mechanism might make the body more vulnerable to the cancers. This is classical clickbait. Even from the bit of the study that they gave, you can see that it was about the health problems of bad sleeping, caused by too much light in the night and possible ...


10

Unlikely. First of all, there are at least five different YouTube videos where people try it out and have no problems. Here is one that includes various sizes and shapes. Secondly, if this were possible, it is likely that cases would appear in the medical literature, but they don't. It is not difficult to find documented cases of light bulbs stuck in ...


10

Not an exhaustive answer, but some pointers: The HESE (Human Ecological Social Economical) Project's Artificial Light in the Environment: Human Health Effects page states "more study is needed". (In other words, "give us more of your money"). It does however cite an exploratory animal study (S.L. Gabby (1961), Observations on the effects of artificial ...


10

The evidence given at that link is not strong, for any of the claims you mention, but especially for SAD treatment. Refs 1 to 6 are about other forms of light therapy, not shining through the ears. Refs 7, 8 & 10 are posters, not from peer-reviewed journals. Refs 11 through 18 are about chemical (not light) treatments for Generalized Anxiety Disorder (...


9

No, it's not true. According to this article in Scientific American, there is a slight additional energy required to start up a fluorescent bulb, but it lasts an extremely brief time: that power surge is so brief that its energy draw doesn't amount to much: the equivalent of a few seconds or so of normal operation, according to U.S. Department of ...


6

@Compro01 said in a comment, There is an assessment by ANSES (Basically the French OHSA in this respect) regarding health effects of lighting systems using LEDs that mentions something about blue light, however, I don't understand French and I'm not sure google translate is giving me an accurate translation of the important bits. The following is my ...


6

I don't have the rep to comment yet, but I think the general answer to your question was covered here. More specifically, I am not sure how Scotopic sensitivity syndrome (SSS) is connected to Florescent lighting and school performance. PubMed has exactly 26 articles on the syndrome, with only one possibly relevant to this discussion. In "Comparison of Irlen ...


6

Yes, light therapy does appear to be an effective treatment for Seasonal Affective Disorder. A study published in the American Journal of Psychiatry compared light therapy to fluoxetine (an SSRI antidepressant) in a double-blind trial. Each participant was given either a dim placebo light and the fluoxetine or a placebo pill and the actual (bright) therapy ...


6

In short, no, the device is a complete hoax, and it was awarded the "Huuhaa" ("Humbug") prize as the worst sham of 2012 by the Skeptic Society of Finland. The first controlled clinical trial of the device in 2011 showed that a placebo works better: When a second test also failed, the company blatantly falsified the results and was caught red-handed doing ...


4

There is plenty of evidence for the speed of light being not relative to the speed of the emitter. Here's a decentish overview. The rules of special relatively form a central part of particle physics and predictions to do with design and construction of Particle accelerators (for decades of research). In these particles are accelerated close to speed of ...


3

In the comments to your question, you ask for percentages. The total electricity production for Europe is approximately 3,200 TWh: Electricity production and supply statistics CIA World Fact Book The savings alleged in the OP are "close to 40 TWh": which is approximately 1% of the total. The first link above claims to be able to measure small percentage ...


2

The claim that installation of blue streetlights in Japan caused a reduction in suicide rates is unproven by research since experts say there’s no conclusive evidence that blue lights will prevent suicide and the effectiveness of the blue lights in this regard has not yet been proven. The limitation for the study in 2013 showing decrease in suicides is that ...


2

There is no evidence that sitting at a computer screen has any effect on the development of age-related macular degeneration or any other retinal problems except for eye straining referring to Dr. Stephen Rose. Patients at risk for age-related macular degeneration who are frequent users of LED computer monitors need to protect their eyes from harmful blue-...


2

There are two parts to this book's statement: 1) That nights with a full moon are colder [than those without] 2) That cold temperature increases hydrogen peroxide formation in dew. For the first part, this stack exchange page addresses the issue of the moon's affect on the weather (summary: negligible): https://physics.stackexchange.com/questions/83574/...


2

Obviously, my source is looking at headlights. However if one has internet access you can look it up. Wikipedia seemed to have the most info in one spot but additional info at other sites would be helpful . Lumens (L) are a measure of the amount of light. Old sealbeams = ?, early halogens = 1550 L later halogens =1820 L newest halogens = 2100 L HID = ...


2

As far as I'm aware, there is a intermediate factor which could explain it: the circadian rhythm In the field of chronobiology, it has already been determined that light plays a major role in synchronization to the circadian cycle. For example see Duffy et al.. The article mentions the "phase response curve", which shows that certain light exposure at ...


1

From the University of Exeter link: A study led by the Barcelona Institute for Global Health (ISGlobal) and involving the University of Exeter found that participants living in large cities with heavy exposure to blue lights at night had double the risk of prostate cancer and 1.5 times higher risk of breast cancer. This was compared to populations ...


1

The conclusion comes from research published in Mapfre's trade journal Seguridad y Medio Ambiente (Security and Environment). "Personal risks posed by LEDs used in everyday devices" The use of LEDs as lighting sources is growing exponentially, not only as domestic lighting but also in terms of personal devices such as smartphones, computer screens, ...


1

The key word is definitely "clouds". In theatres, we do what is similar to the bat signal all of the time, with something called "gobos". Of course, gobos are typically pointed at something solid, which makes them work. Pointed a gobo at a cloud would work, altough not as well, as clouds are not solid. Now, if the bat signal needed to be used on a ...


Only top voted, non community-wiki answers of a minimum length are eligible