Does anybody know if infrared light is visible to normal human eyesight?
457838
No, humans can never see infrared.  It's just a limitation of our evolution.  We evolved to see in the visible spectrum of light, not the infrared.
360845
Yes. those of frequency higher than infra red are absorbed by the PV. IR travels right through the silicon in the PV
329395
Well, first, you have to be specific about what energy.\n\nIf you are standing in a room where your body tempature is greater than the surrounding air, then you are radiating heat, which the naked eye cannot see. However, you can transfer this energy: for example, in the cold, a herd of animals will draw in close and rub against each other to share body heat and reduce exposure to the elements.\n\nThe human body does not emit light, however it does reflect it (otherwise you couldn't see someone). Your eye, obviously, can see light reflected from objects. You cannot transfer light to someone else, in the sense you're probably thinking of.
975165
It depends on the centre frequency and bandwidth of the IR detector.  Glass will absorb certain IR frequencies, very often IR detectors use this as they do not wish to see beyond windows which would cause false alarms.
255650
Yes.  Or at least it can by using deep level optical spectroscopy (DLOS).  See the reference below:
595019
Theoretically, as it is said in the article, it is possible.\n \nLet me explain how we can "see", our eyes have the ability to recognize objects through light. And light, as you already well know I assume, is composed of 7 colors:\nRed\nOrange\nYellow\nGreen\nBlue\nIndigo\nViolet\nIt is known as the ROYGBIV or the spectrum. When light strikes through an object, in this case we will set an example of a blue object, all the other colors are absorbed by the object except for the color blue causing it to strike away to that object. And then it enters our eyes and our brain will interpret is as such.\n\nNow if all of the colors are absorbed, then no light will enter and we see it as black. If all colors are strikes away towards our eyes then wee see it as white. \n\nIt is said in the article that they are gonna use gadgets that will steer light and other forms of electromagnetic radiation AROUND the "cloak" and not to bounce back to our eyes causing it not to have any color at all, not even black nor white. What is that? It is indeed invisible.
270833
1) Generally, rays of the sun which is called radiation lay between 400 nm (nano meter) to 700 nm.\n2) Below 400 nm is called ultra-violet and above 700 nm is called Infra-red.\n3) Both are invisible to the human naked eye.\n4)Infrared radiation is used to obtain pictures of distant objects and the detection of infrared radiation is used by astronomers to observe stars and nebulae.
190626
The visible spectrum (or sometimes optical spectrum) is the portion of the electromagnetic spectrum that is visible to the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light.\n\nCheck the attached link for visible response.
1124852
I would say no.  If you are talking about getting the proper rays to get vitamin D among other things my understanding is that you need the ULTRAVIOLET RAYS for this.  Infrared rays create heat but ultraviolet rays do the chemical reaction thing - so to speak.  \nhttp://www.freewebs.com/eclecticstuff\nUltraviolet rays don't readily pass through glass.  Especially NOT polarized glass like in UV sunglasses.
290359
The energy of a photon is given by E = h*f where h is planck's constant and f is the frequency.  Since photons travel at the speed of light, c, the wavelength is just:\nlambda = c / f.\n\nThe spectrum of light goes from red to violet, where red has the lowest frequency (longest wavelength) and violet has the highest frequency (shortest wavelength).  This means that violet light has more energy per photon than red light.\n\nIn radiation heat transfer, a black body is an object that absorbs all incoming radiation and reflects none (stars are nearly black).  Also, a black body emits a spectrum of radiation based on its temperature.  A plot of monochromatic emissive power vs. wavelength shows the relative "concentration" of different wavelengths of radiation in the total output.  This plot has a characteristic shape given by Planck's Law of blackbody radiation, and it has a maximum at:\n\nlambda_max * T = 2898 micrometers * K = constant\n\nwhere T is the temperature in Kelvin\n\nThus lambda_max is inversely proportional to Temperature.  This means, as the temperature of the emitting body increases, the wavelength at which more of the energy is radiated at decreases (the frequency increases).\n\nI wish I could show you the loglog plot of monochromatic emissive power vs wavelength in Mills page 453.  It shows how low temperature bodies emit in the infrared and negligibly in the visible range and as the temperature increases, the maximum moves toward the visible range.  The sun, at 5800 K has a nice plateau maximum in the visible range which explains why being able to see light is so useful for us.  Another cool thing to see in the plot is that the curve is steeper on the low wavelength side than it is on the high wavelength side: this means that as you increase the temperature of an object, it will glow red and then white because anything hot enough to have its maximum in the violet range also has a large emissive power for everything colder than violet, so all colors of light will be present.\n\nSince a hotter body radiates at higher frequencies, in a sense violet light is "hotter" than red light.\n\nTake a look at the book (or another heat transfer engineering text).  I can't explain very well with only text.
166583
That's light in the visible spectrum. I'd imagine a great deal of compounds could, especially since "great absorbance" means nothing, in scientific terms.
422752
Smoke or fog will work.  There are also 100mW red lasers out there (wickedlasers.com should do the trick) that have some visibility in daylight, but this always depends on there being something (even the tiniest amount of dust) in the air to scatter off of.
1146629
Visible light is within the electromagnetic spectrum.  This spectrum consists of different frequencies such as microwaves, visible light, gamma rays, laser, etc.  Visible light is just a band width within the electromagnetic spectrum that humans can detect with thier senses.  ROYGBIV- red, orange, yellow, green, blue, indigo, and violet.  These are the colors that are detectable by humans within the electromagnetic spectrum and make up the visible light that we see.
622921
An infrared LED is a light emitting diode that emits light in the infrared portion of the spectrum.  Infrared LEDs are commonly used in remote controls.
656295
no, your cones (light receptors in the retina) either respond to certain wavelengths correctly, or they dont.
567266
What is Far Infrared?\n\nWhy Far Infrared?\n\nThe sun is our principal source of infrared heat. As the sun's rays hit the surface of the earth, what we perceive as heat is in fact far infrared heat waves. Infrared heat is essential for all life. Remember the feeling as you lay on the sun-warmed beach soaking up the rays. This is infrared heat in action. Unfortunately you are also receiving the direct damaging ultra-violet rays.  \n\nThe invisible and very safe far infrared heat produced by our Saunas is able to penetrate well below the skin, which enables the body to sweat at temperatures of 110 - 130 F (much lower temperatures than conventional saunas). \n\nTOXINS\n\nToxins in our bodies generally are acidic. Where toxins accumulate, blood circulation is blocked. Far Infrared therapy is effective in expanding clogged capillary vessels and successful in dissolving the toxins into the blood and out of the body via urine and perspiration. \n\nDr. Toshiko Yamazaki, MD, has a clinic in Japan where she continues her medical research in utilizing Far Infrared wave technology. She attributes the success of the FIR wave treatments to the ability of FIR waves to remove toxins from the body. \n\nSWEATING\n\nAnother comparison lies in the process of sweating. Infrared energy created in the Infrared Sauna may induce up to two to three times the volume of sweat produced in a traditional sauna while operating at significantly cooler temperatures (100 to 140 degrees Fahrenheit -- 37 to 55 Celsius -- compared to 180-220 degrees Fahrenheit). The lower heat is safer for those concerned with cardiovascular risk. \n\nBREATHING\n\nOne issue for traditional sauna users has been breathing the exceptionally hot air of 180 degrees Fahrenheit and above. It is distinctly more comfortable to breathe air that is 130 degrees or less, with no loss in heat penetration. As a result infrared sauna users are able to stay in the saunas for longer periods of time resulting in greater benefit.\n\nVENTILATION\n\nTraditional saunas require a closed door to maintain a level of intense heat. Breathing in these saunas has been found to be quite challenging. The Infrared Sauna can be used with ceiling vent, door or window fully open for ventilation. \n\nPREHEATING\n\nOne of the practical aspects of the Infrared Sauna is that it requires only 5 to 10  minutes to warm up compared to 30 to 90 minutes for traditional saunas. The speed of heating and the ease of breathing, coupled with the healing effects, encourage people to use their saunas on a regular basis. One can see the practicality for use in clinics, spas and resorts as well as home.\n\nOPERATING COSTS\n\nThe Infrared Sauna is inexpensive to operate. A 30-minute session, including a 10-minute warm up period, costs about 10 cents ($0.10) for electricity. \n\nINSTALLATION\n\nThe Infrared Sauna takes only minutes to set up. Conventional saunas require building, modifying a room, or creating a separate building, often necessitating the hiring of tradesman. Traditional Native American sweat lodges require labor-intensive installation
913461
"Near Infra-Red" starts at 750nm wavelength (a fixed, accepted value).\nIn theory, and by definition, we CAN'T see it.\nHowever, we are all different: we are not machines built on a standard.\nTo find out if you can see NIR, you have to go to a laboratory, ask for a calibrated source of light and check from say, 650nm to 900nm wavelength radiations.  You will then be able to find exactly your limit for "your" visible.  If it is above 750nm, then you see NIR... officially!\nYou can compare this to your auditive perception: the AF (audio frequencies range, by definition, from 16Hz to 16000 Hz).\nMany of us cannot hear 16kHz, many of us can hear much higher than that!\nIt is all relative.