Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: hamdani yusuf on 22/11/2017 09:07:57
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Is it possible to emulate full spectrum of black body radiation using a device with lower actual temperature?
https://en.wikipedia.org/wiki/Color_temperature#Categorizing_different_lighting
Many other light sources, such as fluorescent lamps, or LEDs (light emitting diodes) emit light primarily by processes other than thermal radiation. This means that the emitted radiation does not follow the form of a black-body spectrum. These sources are assigned what is known as a correlated color temperature (CCT). CCT is the color temperature of a black-body radiator which to human color perception most closely matches the light from the lamp. Because such an approximation is not required for incandescent light, the CCT for an incandescent light is simply its unadjusted temperature, derived from comparison to a black-body radiator.
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In the human visual system, there are 3 color receptors, with maximum sensitivity in Red, Green and Blue.
By mixing combinations of these 3 colors, it is possible to visually imitate the black body spectrum at a particular temperature. This is readily available today in small packages containing RGB LEDs. The temperature of the LEDs remains well below the 3,000-5,000K temperatures they are emulating.
But humans can also sense the Infra-Red part of the spectrum, as a warmth on the hands and face. So if you wanted to emulate this, you could add a high-power IR diode, which would provide the heat component.
But this is really an emulation - 4 narrowband LEDs pretending to be the broadband black body radiation.
The simplest way to provide the true blackbody spectrum is to heat something to the appropriate temperature.
Or, if you are emulating CMBR, cool it to 2.7K (-270C).
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You are reading this on a screen that looks pretty much white, but is near room temperature.
How good does the "emulation" need to be?
If I put some effort into it I could make a "white LED" that was arbitrarily close to Black body radiation at 5800 K (i.e. as hot as the Sun) across the visible spectrum even though it wasn't much more than warm.
But it wouldn't look anything like a black body in the IR or UV (never mind the microwave/ RF, etc)
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You are reading this on a screen that looks pretty much white, but is near room temperature.
How good does the "emulation" need to be?
If I put some effort into it I could make a "white LED" that was arbitrarily close to Black body radiation at 5800 K (i.e. as hot as the Sun) across the visible spectrum even though it wasn't much more than warm.
But it wouldn't look anything like a black body in the IR or UV (never mind the microwave/ RF, etc)
I mean full spectrum, as stated in the title. Now we can emulate any EM frequency, from radio to gamma ray using relatively cool devices (close to room temperature). Can we combine those devices and adjust their intensities to emulate black body radiation?
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[Now we can emulate any EM frequency, from radio to gamma ray using relatively cool devices (close to room temperature). Can we combine those devices and adjust their intensities to emulate black body radiation?
Although it sounds possible in theory there are some practical considerations:
- For each blackbody temperature you would need a large, unique set of adjusted devices from radio masts to X-ray machines.
- some frequencies eg IR would need generators at greater than room temp.
- in some devices the radiation is not the same as blackbody eg what we refer to as radio waves are not the same as blackbody radiation in that part of the spectrum, radio waves are coherent in phase and polarisation, blackbody radiation is not.
- you would need to account for the blackbody radiation of the devices themselves even at room temperature.
Other than that.......
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With our current technology, no.
- Electronics can generate signals up to about a THz
- And optics can generate signals above around 100THz
In-between there is an uncomfortable "Terahertz gap", where our current technologies can't easily produce or detect signals very well. It doesn't help that ordinary objects at room temperature put out a lot of interference in this range, limiting the sensitivity of Terahertz detectors.
See: https://en.wikipedia.org/wiki/Terahertz_gap