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I have a bulb which is hot enough to emit visible light and obviously it's hot enough to emit radiation which lies before the visible light temperature i.e. radio waves, microwaves, and infrared light. So is the bulb emitting radio waves, microwaves, infrared and visible light at the same time?

(I think this is true but not sure as astronomers see stars at almost all light i.e. infrared, UV, Gamma rays, visible etc.)

Thanks in advance!

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For light bulbs and other thermal emitters this is definitely true. Their emission follows the black body spectrum (if you neglect absorption due to the glass container).

If you want to be picky: Any device, which is operated above 0 K (which applies to all devices) emit thermal radiation according to their temperature. This is not directly related with the light generation in e.g. solid-state, semiconductor or gas lasers. Any electrical or optical loss mechanism results in heat generation, which results in some thermal radiation. Yet for my understanding, this is not directly, what was asked for in the first paragraph.

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  • $\begingroup$ I think this is true for all light emitting sources that they emit the light which lies before their max reach of light they emit depending on their temperature (eg- sun's ultraviolate light as well as all the light which lies before ultraviolate light like visible,x-ray, infrared etc) right? $\endgroup$
    – Bhavesh
    Commented Mar 31, 2015 at 10:07
  • $\begingroup$ @Bhavesh Not really, lasers practically do not. $\endgroup$
    – Mithoron
    Commented Mar 31, 2015 at 10:33
  • $\begingroup$ Why? Their temperature is enough for visible as well as infrared, radio and microwave. $\endgroup$
    – Bhavesh
    Commented Mar 31, 2015 at 10:37
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    $\begingroup$ No i am saying that light is emitted depending on how hot is the object. Hotter the object shorter the wavelength of light. $\endgroup$
    – Bhavesh
    Commented Mar 31, 2015 at 12:24
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    $\begingroup$ Nice answer. It might be even better with a graphic showing that for a blackbody at a single temperature, a wide range of wavelengths of light are produced, e.g.: webexhibits.org/causesofcolor/images/content/29z.jpg $\endgroup$
    – pentane
    Commented Mar 31, 2015 at 19:40
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Not all light bulbs are thermal emitters. Fluorescent lights do not use incandescence, hence they would not emit an equal spectrum to an incandescent source with an identical maximal light frequency.

But in general yes objects do concurrently emit a whole spectrum of waves based on their temperature, regardless of whether their light is visible to us.

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  • $\begingroup$ "Not all light bulbs are thermal emitters." For example? Incandescent, CFL, and LED bulbs all emit thermal radiation to some extent, so I'm curious what other kinds of light bulbs exist. $\endgroup$
    – Don Branson
    Commented Jun 10, 2021 at 12:12

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