Wikipedia:Reference desk/Archives/Science/2011 April 4

= April 4 =

defrosting meat with sugar v. defrosting it with kosher salt
I notice that despite the fact that sucrose doesn't split up into Na+ and Cl- ions (the main component of salt's enthalpy of solvation), covering half-frozen meat with sugar will speed up the defrosting process significantly. It's only slightly slower than kosher salt, and it extracts about half the water from the meat that kosher salt would. Like kosher salt, the sugar appears to diffuse into the meat, and also appears to have a protein-denaturing effect, speeding up cooking time. How do I quantitatively calculate the energetics of the two processes? John Riemann Soong (talk) 03:43, 4 April 2011 (UTC)
 * The differences between adding sugar and salt to water vis-a-vis freezing point depression and the van 't Hoff factor are used as a first-year-chemistry exercise in examining colligative properties in a very broad and pedagogical sense, in that it teaches the basic math and concepts involved, but like so much that high school chemistry studenst are taught, reality is far more complex (this is done for a good reason; the same reason that 5 year olds are taught to ride bikes and 16 year olds are taught to drive cars). In truth, the way sugar dissolves is quite different than the way that salt dissolves.  First of all, sugar is a molecule with lots of hydroxy groups on it that lends itself well to hydrogen bonding.  This is why sugar does not dissolve appreciably in cold water, but if dissolved in hot water and then cooled, it forms a stable supersaturated solution known as syrup.  Salt, on the other hand, has a much simpler response to temperature dependence in terms of its solubility; hot water dissolves more, and it precipitates as you cool the water.  This is somewhat tangental to your question, but it does point out the complexity when trying to calculate these things.  If you really want to calculate the enthalpies of solution for both sucrose and sodium chloride, for NaCl the number quoted at Enthalpy change of solution is -3.88 kJ/mol and for sucrose, is quoted here as +5.76 kJ/mol.  In other words, dissolving sucrose is endothermic, so you can't count on that value to explain why it would melt the steak as fast as it does.  As far as cooking differences, adding sugar to a protein like steak will tend to produce more maillard reactions than would adding salt; the steak may not cook faster but it will brown quicker.  -- Jayron  32  04:01, 4 April 2011 (UTC)
 * Are either of these plausible -- won't the meat taste saltier or sweet?  DRosenbach  ( Talk 05:25, 4 April 2011 (UTC)
 * Salting meat before cooking it is one way to increase browning, since salting tends to draw out intracellular juices, which contain some carbohydrates and produces maillard reactions when cooked, and which produces more tasty brown bits. Salt also tends to intensify meat flavors when used appropriately.  Adding sugar will also have a similar effect, but I agree that sweatend meat doesn't sound terribly palatable; I think the best solution is to plan ahead and start defrosting the meat in sufficient time so as to not try to use your seasoning to do the job for you... -- Jayron  32  12:09, 4 April 2011 (UTC)


 * ... and if you do need to defrost in a hurry, hot water is much more effective than either salt or sugar.   D b f i r s   12:57, 4 April 2011 (UTC)


 * No need for heat (which can throw off cooking times and food texture), just immerse in slightly moving cold water (i.e. filled kitchen sink with the tap set to drip). When I try warm water, I also find it more difficult to tell if the item is completely thawed or just the outer layer. Matt Deres (talk) 14:52, 4 April 2011 (UTC)


 * Hot water isn't that effective. With a kosher salt preparation, the meat is fully defrosted by the time I'm done rubbing the chopped garlic, ginger, among other Asian-y spice preparations into the meat. (It's two birds with one stone.) And then when I wash off everything (including the kosher salt), a lot of flavour has been absorbed. I'm also really curious about the hysteresis of syrup. Is there a resource that covers this? John Riemann Soong (talk) 18:49, 4 April 2011 (UTC)
 * This is a cook's answer rather than a chemist's one. You can rub a steak with a mix of salt and sugar, and it will not come out too sweet. Will contrast well to a sauce including wine or balsamic vinegar. Similarly, for cured meats like bacon, use a mix of sugar and salt for best results. Or, for the wet cure of Wiltshire ham, salt, sweet cider and apple juice. "Sweet-cured" bacon is available in the shops. Itsmejudith (talk) 20:47, 4 April 2011 (UTC)

Tool to calculate what temperature I need to change the air to, to achieve a desired Relative Humidity (RH)?
Apparently, if the temperature is

Temperature     : 18ºC, and the relative humidity is: Relative Humidity: 65%, if I heat the air to: Temperature     : 35ºC, the would give a relative humidity of: Relative Humidity: 24% Looking at the chart on the right, you'll see that this is correct, but, I need a better way to calculate this on the fly.

For example if the temperature is 25ºC and the RH is 60%, to what temperature to we need to heat the air to achieve a RH of 50%?

220.244.35.181 (talk) 10:21, 4 April 2011 (UTC)


 * You need 2 pieces of information, the vapor pressure of water at a given temperature and the desired relative humidity. Since RH = dew point/vapor pressure x 100, first use the current RH to find the current dew point, then find the temperature at which that dew point is exactly 50% of the vapor pressure, and viola... For your figures, if the temperature is 25 degrees C, the vapor pressure of water at that temperature is 3.2 kPa.  If the RH right now is 60%, that means that the dew point is 0.6*3.2 = 1.92 kPa.  If we want the temperature at which the current conditions will produce a 50% RH, we just do that backwards, 1.92 = 0.5*X, X=3.84 kPa, which occurs at a tad more than 28 degrees C.  So the answer to your question is about 28 degrees C.  You can do the same calculation for any set of conditions, so long as you know the current temperature and current RH.  -- Jayron  32  12:06, 4 April 2011 (UTC)
 * One minor correction to my answer. Its not the dew point per se, it is the actual partial pressure of water vapor in the air right now, which is the same as the vapor pressure of the dew point temperature.  My calculations still hold, but my terminology was a little sketchy.  -- Jayron  32  12:15, 4 April 2011 (UTC)
 * Excellent answer, and helpful, in particular the formula undefined, but perhaps there is an existing tool for this out there or a simple formula I could put into Excel? Actually, I'm a computer programmer - I can write a tool, but it will be based on a table of values instead of a perfect mathematical formula - but I'm satisfied with this compromise. Thanks :) 220.244.35.181 (talk) 12:34, 4 April 2011 (UTC)
 * Sure. You can combine the two equations into one based with some simple algebra, and get RH1 * VP1 = RH2 * VP2, where RH = Relative humidity expressed as a decimal fraction and VP = the vapor pressure of water at the given temperatures.  If you wanted to do this in Excel, just copy the Temperature vs. Vapor Pressure data into the spreadsheet for easy referencing, and use a modified form of the equation VP2 = (RH1 * VP1)/RH2 and just look up the temperature associated with the target vapor pressure.  It should be trivial to set up formulas in excel to do the calculation for you, but the calculation is simple enough with the table of vapor pressure data and a calculator you shouldn't need to go through that trouble.  -- Jayron  32  14:03, 4 April 2011 (UTC)
 * OH, I see what you are asking. You could use the standard form of the Clausius-Clapeyron equation, using the latent heat of vaporization of water, via:


 * $$\ln \left(\frac{P_1}{P_2} \right) = - \frac{\Delta H_\mathrm{vap}}{R}\left(\frac{1}{T_1} - \frac{1}{T_2} \right),$$


 * If you use P1 = 1 atmosphere (760 torr or 101 kPa) and T1 = 373 kelvin (100 degrees C)(BP of water) you can find the vapor pressure of water at any other temperature. I am pretty sure that is how the table is set up.  That will work better than the Antoine equation. -- Jayron  32  14:14, 4 April 2011 (UTC)
 * R, by the way, is the Gas constant, in this case the units for R should be the same as those for ΔHvap... -- Jayron  32  14:18, 4 April 2011 (UTC)

Optical "Jacks" on the Back of my TV and Blu-Ray Player
Good Morning-- A month or two ago, we purchased a Vizio HDTV. On the rear panel, it has a space marked "Optical," with an almost-square, translucent plastic sensor. I have something plugged into almost every one of the other jacks (Coaxial, AV, PC, USB, RGB, HDMI), but have yet to figure out how this one works or what I could use it for. I found an owner's manual online that says
 * "When a digital audio signal is associated with an input which is selected for viewing, the digital audio associated with digital programming will be available on this SPDIF Optical connector for connection to your home theatre system. The white color band on the rear of the TV indicates this connection."

Over the weekend, we treated ourselves to a Vizio Blu-Ray player that was on sale. It has a similar Optical "jack" on its rear panel as well. Should I understand, then, that the audio signal will be transmitted from the Blu-Ray player to the TV without a need for a cable? Please forgive my newbie-ness, and thank you for your help!  Kingsfold  (Quack quack!)  12:01, 4 April 2011 (UTC)


 * You will need a S/PDIF connector cable. --Mr.98 (talk) 12:09, 4 April 2011 (UTC)
 * Mmm hmm. I did some further reading after posting this and also figured that out. In the words of Chris Farley, "I feel like a horse's patoot."  Ha ha.  Thanks much.  Kingsfold   (Quack quack!)  12:16, 4 April 2011 (UTC)


 * Additional pictures of the connector format (for the curious) at TOSLINK. TenOfAllTrades(talk) 12:30, 4 April 2011 (UTC)


 * I'm not sure that this is a science question but anyway if you use HDMI in theory everything including audio should just work. Presuming you don't run in to HDCP issues. Nil Einne (talk) 18:09, 5 April 2011 (UTC)

Selenium oxidation
Would oxidation of L-selenomethionine produce red or black selenium? In my case, electrolytic oxidation produced a black residue. Thanks, --Chemicalinterest (talk) 12:25, 4 April 2011 (UTC)

Removing Hydrophobic Silicon Product from car windscreen
I have been using Rain-x on my windscreen with brilliant raindrop repellant effect but I have been told that another product has much longer lasting and non-misting qualities. But before I try the other product will I need to remove the Rain-x and if so, how? Thanks in anticipation. 92.4.40.87 (talk) 14:33, 4 April 2011 (UTC)


 * If it's oil-based, then dish-washing detergent should do the job. StuRat (talk) 19:05, 4 April 2011 (UTC)


 * Thanks Stu. I must confess to doing a bit of research since posing my question (which I should have done first off eh)? It is apparently a silicone based product that really sticks to the glass and which other users have had great problems removing. Oddly enough, the manufacturesr's own website suggests using a VERY mild abrasive such as Cif. But thanks again. 92.4.42.68 (talk) 20:03, 4 April 2011 (UTC)


 * Silicone greases are hard to remove. Go ahead an try detergent by all means, but I think you may find it insufficient.  When using silicone oil in a chemistry lab, it's standard practice to use a base bath, often a sodium hydroxide in alcohol .  Silicone grease is used in the laboratory because it is pretty resistant to typical organic solvents (as well as fairly non-reactive). Buddy431 (talk) 20:22, 4 April 2011 (UTC)


 * Beware that some of those things might damage the paint. StuRat (talk) 06:50, 5 April 2011 (UTC)


 * Wouldn't it be easier and more economical to wait until the existing coat of Rain-x has begun to wear off? That way the rest will be easier to remove, and you will have had the benefit of what you have already paid for. {The poster formerly known as 87.81.230.195} 90.197.66.111 (talk) 00:59, 5 April 2011 (UTC)


 * Or, just mix the new with the old. Is there any reason to think they won't work and play well together ? StuRat (talk) 06:50, 5 April 2011 (UTC)


 * Hi Stu - again. If you read my question again, you will see that I have been advised of a longer lasting and non-misting/smearing product than Rain-X. That is what prompted my question in the first place, as I don't know if Rain-x and the new product Enduroshield will co-exist. But thanks for your interest. 92.4.43.217 (talk) 18:22, 5 April 2011 (UTC)


 * I suggest you mix them together over on the passenger side, so that if the resulting mixture fogs up, it won't block your vision. My guess, though, is that mixing them will be fine. StuRat (talk) 23:23, 6 April 2011 (UTC)

Can I repair a laptop charger with graphite?
To preface: (A) My laptop and its components are under warranty, and I can certainly send the charger back for replacement; and (B) even buying a new charger outright is not prohibitively expensive-- they're like $20 or so. However, just for a challenge of it, and to feel like I could fix something, I'd like to try to repair it on my own. I have a HP DV6646US laptop. The charger (or an extremely similar one) is pictured here. Thanks to having two sons in the house (almost 9 and almost 4) that use the computer, the small cylindrical piece that plugs into the laptop has been jerked back and forth too many times, and the connection between that and the contacts beneath it (within the black plastic end of the cord) has been severed. We can still usually achieve a power connection by holding onto the cord, pinching the metal end of the charger, and simultaneously twisting and pushing in an attempt to seat the piece so it touches the contacts. However, if the laptop gets bumped, the power connection is usually lost, and we then repeat the process. Recently, to investigate, I completely removed the metal end. On it, there seems to be a small bump off to the side, as well as a smaller (than the cylinder) metal piece coming off the bottom-- the part that actually touches the power contact. Shining a light down into the plastic casing reveals where the end must contact, and a small cavity corresponding to the bump off to the side of the metal part. Now the question. I was reading on a different section of the Reference Desk this morning and learned that Graphite conducts electricity. (Didn't know that. Learn something every day.) Might it be possible for me to either pack the plastic casing with graphite flakes enough to ensure a contact, or hand-shape a "bridge" out of a large pencil lead? What's the consensus? Might this work? Sorry this is so long. Just wanted to be as clear as possible. Thanks!  Kingsfold  (Quack quack!)  15:26, 4 April 2011 (UTC)
 * You may be able to work out a fix yourself, but be aware that doing this yourself may likely invalidate the warrenty for the whole computer, in other words if you try your homebrew fix on the charger, and then later something unrelated goes wrong with the computer, and you CAN'T fix it, if you try to get HP to fix it under the terms of the warrenty, they can refuse to do so, since you invalidated it by trying to fix the charger... -- Jayron  32  15:30, 4 April 2011 (UTC)
 * Also, graphite conducts, but it also crumbles and might go anywhere, possibly producing a short. If you want to fix it yourself (which, really, is not recommended - get a second one while HP fixes the first under warranty), get a suitable plug, cut off the cable and use some solder to re-attach everything where it belongs. --Stephan Schulz (talk) 15:55, 4 April 2011 (UTC)
 * Good advice all. It's one of those extended-warranty deals, not from HP directly, but yes-- I hadn't considered what they on the other end would think if the defective charger came back packed with graphite.  Ha.  My most likely plan was always to buy a second one and have the first one replaced, and almost certainly what I'll do.  But... is the science of it valid?  If I could somehow shape a disc of solid graphite and seat it down in there, and then put the metal part back in, it would most likely carry the charge, correct?   Kingsfold   (Quack quack!)  16:02, 4 April 2011 (UTC)
 * Possibly, but this is a "devil is in the details" situation. The exact composition and grade of the graphite will have a lot to do with performance, and its not as simple as cramming a pencil lead in there.  So, while the replacement piece will be graphite, it needs to be the right graphite and your chances of jury rigging the thing yourself the right way is pretty slim compared to you just screwing it up.  -- Jayron  32  16:26, 4 April 2011 (UTC)
 * Yes. Also, you can make resistors by drawing lines of various thickness and length with a (graphite) pencil on paper. Again, that's something recommended if you are alone on an island and need to fix your radio, not for production use. When I was much younger and much much stupider, I "fixed" the fuse on my cassette player by winding the contacts with soldering wire. I like to believe this was in the low-voltage part now ;-). --Stephan Schulz (talk) 16:31, 4 April 2011 (UTC)

Don't do it unless you want to buy a new computor. the socket where the plug fits is not one contact, it is two,and they must be kept seperate. the equipment is polarity sensitive, which means that if you accidentally put power to the wrong contact you may fry your computer.Just ramming some graphite in the hole won't do it. If you just want to fix something for the experience, you would do much better with something less technical. something less prone to expensive destruction. Maybe your kid's toy car,A window, The squeaky garage door. Electronics is not the way to start.190.56.16.64 (talk) 17:27, 4 April 2011 (UTC)
 * I'd worry about what could happen with stray flecks of graphite if they somehow get into the laptop. Wnt (talk) 00:13, 5 April 2011 (UTC)
 * Please note that pencil graphite has a significant amount of binder in it. It is not pure graphite. Copper typically has a resistivity of 17E-9 Ohm.m whereas pencil graphite is about 3E-5 Ohm.m that is 3.5 orders of magnitude. It is significant. —Preceding unsigned comment added by 92.20.201.71 (talk) 01:44, 5 April 2011 (UTC)

Are monkeys able to throw darts?
Or is this just an allegory for something extreme imprecise? Quest09 (talk) 16:33, 4 April 2011 (UTC)


 * I don't see why a monkey couldn't move his harm and hand in such a way as to cause a dart to fly through the air. The idea of "monkeys throwing darts" just refers to randomness; it is unlikely that said dart thrown by said monkey will be precise enough to hit the bullseye... -- Jayron  32  16:44, 4 April 2011 (UTC)


 * Maybe, they need fine motor abilities to throw a dart like a dart (instead of throwing it like a stone). Quest09 (talk) 17:19, 4 April 2011 (UTC)


 * True, but that they are able to throw a dart at all makes them substantially different than, say, a three-toed sloth or a bald eagle which wouldn't be able to throw a stone or a dart or really anything... -- Jayron  32  19:35, 4 April 2011 (UTC)


 * As Jayron points out, the usage is largely metaphorical. However, I see no reason why any number of monkey species couldn't be trained to throw darts. They do throw things as a natural behavior, and their limbs are mechanically close enough to ours. On a related note, here is an amazing image of an ape that has learned how to spear fish by watching people . SemanticMantis (talk) 17:40, 4 April 2011 (UTC)


 * To be clear, he's just sticking a fish already caught by humans, not launching a spear at a moving target and hitting it: "Although the method required too much skill for him to master, he was later able to improvise by using the pole to catch fish already trapped in the locals’ fishing lines". So, I'm skeptical that any existing primate other than humans could throw a dart with any reasonable chance of hitting a small target, point first. StuRat (talk) 18:15, 4 April 2011 (UTC)


 * Yes, I didn't mean to indicate the orang was throwing a spear to hit a moving target, thanks for clarifying. However, I don't share your skepticism. Given suitable training, I think many primates could successfully stick a dart into a standard target from standard distance. SemanticMantis (talk) 18:54, 4 April 2011 (UTC)


 * In case anyone is interested, here's a nice scholarly article comparing throwing behaviours in humans and capuchins . Capuchins are pretty good throwers, they would be good candidates for dart training. SemanticMantis (talk) 19:04, 4 April 2011 (UTC)


 * I didn't see anything in the abstract about the how their accuracy compares to that of humans. And, with darts, there's the extra element of having to keep the dart in a certain orientation as you throw it; you can't just toss them like rocks. StuRat (talk) 06:47, 5 April 2011 (UTC)


 * The Dart-Throwing Motion of the Wrist: Is It Unique to Humans? PrimeHunter (talk) 01:13, 6 April 2011 (UTC)


 * Wow. StuRat (talk) 23:20, 6 April 2011 (UTC)


 * yes, I do thought it was metaphorical, just wanted to confirm it. Quest09 (talk) 17:58, 4 April 2011 (UTC)

Bold for first instance of abbreviations in journals?
I've sometimes seen articles written so that the first instance of an abbreviation (abbr.) was inserted in bold, which made it easier to find when reading further down in the text and having forgotten the expanded form of the abbr. Does anyone know any journals which do this? --129.215.47.59 (talk) 17:24, 4 April 2011 (UTC)

Himilayan glacial meltwater
I saw a "documentary" on PBS on US TV that seemed to suggest the following:

1) Due to global warming, the Himilayan glaciers will melt.

2) Once they do, they will no longer provide glacial meltwater to the major Indian rivers (Ganges, Yangtze, and Yellow River).

3) Those rivers will then dry up and millions who depend on them to irrigate their crops in China and India will starve.

This seems like questionable logic to me. If we assume that the precipitation falling in the Himilayas remains the same, then that same amount of water should still find it's way into those rivers. Is the issue that they think less precip will fall ? Or is it that the water will all flood down in the spring, and the rivers will then dry up in summer ? Or is it that glaciers even out precip cycles from year to year by acting as a buffer ? Do we have an article on this ? StuRat (talk) 18:07, 4 April 2011 (UTC)


 * That part of India has a monsoon climate. One of the characteristics of such a climate is that most of the rainfall for the year happens during a short span of months.  For example, parts of India may get ~80% of their rain during only three months of the year.  Snowfall / glaciers in the Himalayas provide a buffer.  Some of the precipitation accumulates there and melts slowly over the year providing feed waters for the major rivers even in the dry seasons.  If it gets hot and the glaciers completely melt away, the fear is that precipitation in the Himalayas will fall as rain that simply washes away rather than being stored.  If that happens the rivers could run much higher during the wet season, resulting in frequent floods, and then run very low during the dry season, leading to droughts.  Dragons flight (talk) 18:41, 4 April 2011 (UTC)


 * This talks about possible links between global warming and changes to the monsoon. This discusses links between Himalayan snowfall and the monsoon (and thus the growing season). -- Finlay McWalter ☻ Talk 18:45, 4 April 2011 (UTC)


 * (EC) The glaciers store water precipitated in the wet season, and deliver it during the dry season. Your last idea on buffering is the closest to correct. SemanticMantis (talk) 18:47, 4 April 2011 (UTC)


 * Aren't mountains the source of the annual flooding of the Nile? Maybe this effect in India and China is similar. 63.17.91.115 (talk) 03:38, 5 April 2011 (UTC)


 * Mountains without glaciers can still buffer precipitation, by means of snowpack and groundwater. The mountains of California (including the Sierra Nevada as well as the less-famous but very important Klamath Mountains) perform this function in spite of having almost no glaciers.  At the altitudes where glaciers form, snowpack can persist almost year-round.  However, snowpack may be a less effective buffer than glaciers if it becomes depleted more rapidly.  --Smack (talk) 04:10, 5 April 2011 (UTC)


 * Glaciers also form a permanent cold surface onto which snow can accumulate even early in the season. Bare rock will be warmed by the sun, and will thus melt more of the years snow. --Stephan Schulz (talk) 06:42, 5 April 2011 (UTC)

OK, thanks everyone. StuRat (talk) 18:21, 8 April 2011 (UTC)

Human height and calcium
Our article Human height discusses how "good nutrition" is of great influence on height, giving several examples; but I haven't found an explanation of what nutrients are responsible. I immediately thought "Calcium!", and that article quotes an osteoporosis organization as saying that calcium is of great importance to bone density; but it does not mention bone length. The human height article claims that in the 1700s and 1800s, "Europeans in North America" were "far taller" than their European counterparts, and Netherlanders were shorter than other Europeans; but Britain and the Netherlands of the time were not impoverished, so I'm confused what nutrients were missing in Europe that seemed to stunt growth. It seems unlikely that only tall Europeans migrated to North America and interbred to produce "far taller" children.

I wondered as a layman whether human dairy consumption, which started around 6000 BC to 5000 BC according to our Milk article, had started an upward height trend among us humanoids; but the Calcium in biology article makes it look like there are several foods which I think were probably widespread that have more calcium per pound than fluid milk; and some large majority of humanity seems to have been lactose intolerant for the first few thousand years that some people did consume fluid milk ... so that theory seems pretty shaky.

So, what nutrients exactly are thought to be primarily responsible for the "good nutrition" influence on height? Comet Tuttle (talk) 18:42, 4 April 2011 (UTC)


 * Protein seems to be one factor. The body reacts to a lack of protein by stunting growth, so you get reasonably healthy, but smaller, people. StuRat (talk) 19:33, 4 April 2011 (UTC)


 * I have to disagree that English people, at least, were not improverished in the 17 and 18 hundreds. Starving to death was quite commonplace, I forget the medical euphanism used at the time, and food was very expensive. Due to poverty many people had very bad diets that did not provide the full range of nutrients. See for example http://www.bmj.com/content/337/bmj.a2722.full 2.97.220.102 (talk) 21:12, 4 April 2011 (UTC)


 * See Corn Laws for one of many relevant factors in the malnutrition of the time. And, not to get too Humanities on the Science desk, "Oh God! that bread should be so dear,/And flesh and blood so cheap." 86.164.73.72 (talk) 22:32, 4 April 2011 (UTC)

Infra red absorption
Does dark colored skin absorb infra red more thn light colored skin and therfore make the person with darker skin feel warmer under the same illumination--78.150.224.119 (talk) 19:07, 4 April 2011 (UTC)


 * Not answering for skin color specifically, but something dark in the visible spectrum isn't necessarily "dark" in the IR spectrum. Also note that dark objects also radiate more, so that might tend to balance out. StuRat (talk) 19:43, 4 April 2011 (UTC)


 * Energy is being received over all wavelengths, including UV, Visible, and IR. A dark material will absorb more visible light. As StuRat points out, the emissive properties of the dark material may be different. Niluop (talk) 07:46, 9 April 2011 (UTC)


 * We had exactly this question not long ago, but I can't find it... can anyone else? --Tango (talk) 20:02, 4 April 2011 (UTC)


 * about two days ago, it got swiped out just after I answered that it was hard to find a way that could compare subjective feelings of warmth. Is that active or passive feeling? Richard Avery (talk) 21:57, 4 April 2011 (UTC)

Keeping PIR-controlled light on
The lights at work are PIR controlled and I keep having to get up and wave my arm about. Is there some device that will produce IR light every 10 minutes, say, to keep the light on? --129.215.47.59 (talk) 20:07, 4 April 2011 (UTC)


 * Place one of these objects (pictured to the right) somewhere in front of the sensor. Comet Tuttle (talk) 21:48, 4 April 2011 (UTC)
 * Do they also have a manual switch? I've seen some PIR lights where the timer can be defeated by switching them on and off then back on quickly. Don't know how common that feature is but worth a try. Vespine (talk) 22:29, 4 April 2011 (UTC)


 * Ribbons, or strips of aluminised-mylar balloon, hanging from the air-conditioning vent. Stick a Post-It over the sensor when you go home, so the lights don't stay on all night. Similarly, try a child's pinwheel in a location where the AC moves it and the sensor sees it. -- Finlay McWalter ☻ Talk 22:44, 4 April 2011 (UTC)


 * Excellent suggestions, all. A while ago when I worked in Facilities Maintenance, we looked after some very large open plan offices with motion-sensor controlled lights. Some who worked late when their neighbors had left could wave their arm to reactivate the lights, but on one floor, one habitual late worker was out of the sensors' lines of sight and complained of being frightened by most of the lights going off and her having to get up and walk a couple of paces to bring them back on. I suggested placing a similar cheap executive toy (with swinging magnets) visible to the sensors so as to keep the lights on, but nooo, we had to rewire the floor's lighting circuits with wall switches at a cost of several hundred pounds. {The poster formerly known as 87.81.230.195} 90.197.66.111 (talk) 01:16, 5 April 2011 (UTC)


 * I don't think those ideas will work because PIR sensors rely on moving sources of IR radiation. The switch on and off didn't work, either but thanks. 129.215.47.59 (talk) 20:25, 6 April 2011 (UTC)