All Questions
Tagged with thermal-radiation visible-light
139 questions
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Why is there a colour difference between stars and hot objects since they are both black-body radiators? [duplicate]
I have a question about the color of a black-body radiator that has been baffling me for a few years now, and I haven't been able to find a satisfactory answer. So, we know that a star's color depends ...
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Why does Sun appear white at noon?
I have found several source citing the reason for the white apperance of sun is due to less scattering of light before sunlight reaches an observer on the Earth (as it is relatively closer to us at ...
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2
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Why can't we see green color in the sky? [duplicate]
From sunrise to sunset we can see a variety of colors in the sky.
For example, during morning the most dominant color is blue whereas during sunset orange,red,yellow and there shades are more dominant....
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How to measure light intensity in a room?
Does anyone know how I would go about measuring the light intensity in a room? I'm not interested in knowing the lux reading, I would like to measure the $W/m^2$ due to thermal radiation in my ...
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Any research or study that monitored the spectrum of the natural light during the entire day?
I am interested in understanding the light spectrum during sunrise, morning, midday, afternoon, golden hour, and blue hour.
Is there anyplace I can look at those?
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Black Body radiation and radiation in general [duplicate]
So I'm learning about blackbody radiation and radiation in general. As I understand it, there are 3 ways to transfer energy/heat: Convection, Conduction and Radiation. In chemistry I also learnt about ...
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Why are the hottest stars appear mostly in blue or blue-white? [duplicate]
Does it have to do with anything regarding wavelengths and frequencies..
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Can an atom according to Bohr's model be considered a black body?
I recently read about Bohr's atomic model and found out that an atom tends to absorb all the energy of a particular frequency to excite its electron and it also gives the same amount of energy that it ...
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Color temperature and space
I often think about the universe and lately about the color spectrum. so I wanted to ask how much the temperature of the body depends on the color. the hottest star I've found is 200,000 k and its ...
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4
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Why does a blackbody object emit light if it only absorbs light?
I have learned that a blackbody object only absorbs light and thus does not reflect any light. The blackbody object will, however, emit light, and none of this light is due to reflection. Where does ...
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What are the hex color code equivalents for the different classifications of stars?
Stars appear to be of various colors based on the visible light they emit. I am wondering if there is a hex color code that can be considered to be typified or average for the various classifications ...
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A question about colour temperature
This picture from Wikipedia is a table of temperatures vs colour for incandescence, however the problem is that I’ve been told that for a black body, even something with a temperature of say 2000C (E....
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Why is the solar spectrum at the surface of the Earth strongest in the visible light range? [duplicate]
I watched a CrashCourse video saying that nuclear fusion of $\rm H$ to $\rm He$ in the sun radiates mostly gamma rays. Then why are the lights that come to Earth comprise mainly of IR & visible ...
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How is the Kelvin temperature of a light source or an image is calculated?
I searched for it but couldn't find any answer for this.
For a light source is it simply the average of the full spectrum power?
And how do you compute it for an image? How can you tell the difference ...
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Why does UV light feel warm on my skin? Whereas infrared light heats up space around me plus my skin?
Noticed something weird today.
I have an infrared space heater that is pretty good at heating up my desk at work (as well as my skin obviously).
I also have a UV flashlight. I noticed the UV ...
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Does a blackbody always appear black?
By definition an ideal black body ⚫️ is a complete absorber that is no radiation in any spectrum goes reflected by it , which suggested that it should appear dark or black
On the other hand by ...
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If all matter can emit at all wavelengths, can all matter absorb at all wavelengths too?
Based on Planck’s law all matter can emit at all wavelengths at different intensities dependent of temperature. I was wondering if this holds true, does all matter absorb all wavelengths too, at ...
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Is the Drapers point inaccurate?
Is the Drapers point faulty since an oven glows visibly red without it actually reaching Drapers point? When the Drapers point blackbody radiation frequency is calculated by Wien's law it results ...
user348071
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Do all objects at the same temperature glow the same color?
Does Kirchhoff's law for heat radiation imply that all objects at the same temperature will glow the same color?
In other words, if a piece of molten iron glows the same color as my body, which ...
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What percentage of sunlight isn't scattered by the atmosphere?
What percentage of sunlight isn't scattered by the atmosphere and instead will arrive at your eyes directly from the sun.
It's been aksed here before but a proper answer hasn't been given.
I was ...
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Why do dark objects absorb visible light but only emit infrared radiation?
What is it about the molecular structure of dark coloured objects that means they absorb most of the visible light that falls on them, but radiate infrared?
Naively I would think that if a molecule ...
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Diffrence between thermionic emission and photoelectric emission
Thermionic emission involves heat energy to excite the electron and remove it. In the photoelectric effect, a beam of light is involved.
As per my understanding heat and photons, both are energy. Heat ...
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Aren't all objects luminous in a sense?
In my physics class, I learned about "nonluminous objects" - these are objects which don't produce their own light. But, don't all objects emit light by black body radiation? So are all ...
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Diameter of a spherical cavity at temperature 500K necessary to make deep red light at 100 cd/m²
This is a thinking experiment, I'd just like some help in reasoning.
When a cavity is heated it emits electromagnetic radiation depending on its temperature.
Say the cavity C is made of a white, heat-...
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Black-body radiation and visible spectrum of stars
I've done some reading on black bodies and black body radiation, after reading that stars are considered black bodies. As such I think the black bodies absorb all light, but also put off a radiation ...
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If you were invisible, would you also be cold? [closed]
If you were invisible, would you also be cold? (Since light passes through you, so should thermal radiation.)
Additionally, I'd like to know if you were wearing invisible clothes, would they keep you ...
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Is the temperature of light affected by color filters?
This video demonstrates how varying color filters alter the energy of photoelectrons emitted from a light source:
https://www.youtube.com/watch?v=kcSYV8bJox8
But I am confused by what these different ...
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Black body radiation: why can it glow yellow?
With black body radiation, light of different wavelengths are emitted in various proportions depending on the temperature of the emitter.
Graphs of spectral radiance vs wavelength for different colour ...
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Color temperature
To grow plants with artificial light, I need a device that can measure the wavelength of light and make sure I get the desired wavelength to the plant. This device is very expensive. Can I use the ...
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What is the wavelength of white light? [closed]
Does white light have a wavelength, and I know that the sun emits white light, but the atmosphere makes it refract to make it appear yellow to us. Do all the stars in the universe emit white light?
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Color of a flame [duplicate]
I use an LPG (liquefied petroleum gas) gas stove at home for cooking purposes. I notice that, in the flame, the bottom part is almost always blue but the top has a yellowish-orange color. Why is that?
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How is light emitted by an incandescent lamp?
I am looking for better understanding of how light is produced in an incadescent lamp. More specifically: how is the kinetic energy of electrons converted to light?
Are we dealing with interband ...
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Wien's law and colors
I know there are a Wien's law for frequency and one for wavelenght, but I'm wondering which one is the most accurate when it comes to our perception of colors.
For instance for the Sun, the Plank ...
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Why does the sky after sunset mimic the blackbody spectrum?
There are several answers on this site and elsewhere about why the sky is blue and why sunsets are reddish. But I could not find anything that discusses the relationship between the blackbody spectrum ...
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What is black-body equivalent of UV part of solar spectrum?
If all non-UV light was filtered from sunlight, does this approximate a different type of black body radiation? Regular sunlight has a black-body temperature of 5777 K.
This is in relation to the ...
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Why are infrared images not great?
Why are infrared images not great?
Simply googling infrared images, and looking at pictures of things like streets, people, animals, etc. . . I can't quite pin ...
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Why is it called a "black" body?
So I know a black body is a perfect absorber and perfect emitter... It doesn't have to be black, but why is the term "black" used? In my textbook, it says that "at lower temperatures, a ...
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Black body radiation and why do we see different colors?
I am high school student and I am really confused about how black body radiation or radiation from any general body works?
Suppose we are observing the color of any body is green, does it mean that it ...
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If the moon became a black hole, how much lower would the temperature be on Earth's surface?
I read that if the Sun became a black hole the Earth would become colder, but the effect would be negligible because the mass of the hole is still there so there would still be tides.
But, how much ...
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Considering the history of microwave Background radiation, was it ever in visible range? When will it fall to be able to heat water like in our oven?
Please do provide assurance of what formula you used and that you did the calculations for the answer. Thanks.
My back of letter calculation says that CMBR was never in visible range since it became ...
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Specular Reflection of IR Light
I have started to use thermal imaging cameras more and more and realized that I can see the reflection of my self bouncing off of a glass window through the IR camera. When viewing it on my monitor, I ...
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2
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How do we determine the color of heated glass?
If a glass of certain colour is heated, then how can we determine the corresponding colour that it will glow with?
For eg: I saw a question that asked "A blue glass when heated will glow with ...
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Is it dangerous or safe to use a black/dark cloth cover on a propane tank? [closed]
Say I have a standard 20lb propane tank.
I want to put a protective cover over it, to shelter it from weather.
Can I use a cover that is black or dark colored? Is that dangerous or will it put me at ...
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Deeper underlying explanation for color-shift in Wien's Law?
Suppose we have a blackbody object, maybe a star or a metal (although I understand neither of these are actually blackbody objects, to some extent my understanding is they can approximate one). ...
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Colour temperature and emission spectroscopy
If blue light is emitted from excitations below 500C for example potassium in a flame emits purple photons but only has to be 500C for it to do so, then how do we know if the sun is yellow hot or if ...
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How much hotter will an object get if I paint it black?
I have read these threads
If black is the best absorber and radiator, why does it get hot?
Black and white matters. But why and how?
If a black body is a perfect absorber, why does it emit anything?
...
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If black is the best absorber and radiator, why does it get hot?
I can guess that it’s emission peaks at a higher temperature than white. So when a light is turned onto a black and white piece of paper, the initial condition is not at equilibrium. As black absorbs ...
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Is the yellow Sun light produced by photon scattering inside the Sun?
If the hydrogen emits four distinct light frequencies as a gas and on the Sun surface the gravity cannot alter hydrogen state as a gas does the yellow component of sunlight come from its interior?
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From a photon momentum perspective, why do dark surfaces absorb more heat?
We've all been taught that dark surfaces heat up faster, since they absorb photons, while light surfaces heat up slower, and reflect photons. But I can't reconcile this with momentum transfer.
When a ...
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Which would keep you cooler? A black canopy tent or a white canopy tent?
I was outside recently at a function and they had two colours of canopy tent set up: black ones and white ones. I was wondering which one would be cooler to sit under. The white one would reflect the ...
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