The brightness and color of the extremely bright light produced by the Space Shuttle SRB's is discussed in this answer and in comments below it, though the main subject there is the dim blue light produced by LOX/LH2.

What physical process produces the radiation that makes the Shuttle's SRB exhaust so incredibly bright? Is it still blackbody radiation from particles, though they are partly aluminum based now, or is it more due to luminescence from other molecules in the exhaust?

Does the oxidant for the aluminum contain oxygen? Are there glass "soot" particles in the exhaust?

Or is there just a lot of carbon-based soot that's also produced, but the bump in temperature from the aluminum oxidation makes it so much hotter that it's so much brighter?

There is some related discussion at the question How do rocket propellant combinations rank in terms of “brightness”? as well, which currently has no accepted answer.

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  • $\begingroup$ Should I copy my answer from your question? What is wrong with Kirchhoff's law of thermal radiation and gas mantles? $\endgroup$
    – Uwe
    Commented Mar 25, 2018 at 10:51
  • 2
    $\begingroup$ In my opinion the radiation is not from the gas, it its from solid aluminum reaction products. A gas mantle is much brighter than the gas flame alone without mantle. $\endgroup$
    – Uwe
    Commented Jul 30, 2018 at 19:27
  • 1
    $\begingroup$ This chart deck seems like it might be relevant to the discussion: osti.gov/servlets/purl/1119784 $\endgroup$
    – Tristan
    Commented Nov 30, 2022 at 14:50
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    $\begingroup$ @Tristan yes, thanks! From that, also found Measurement and Analysis of Aluminum Monoxide Flame Emission Spectra $\endgroup$
    – uhoh
    Commented Nov 30, 2022 at 20:54
  • 1
    $\begingroup$ One note: blackbody only gets you color temperature, not brightness. I would wager that the aluminum products being in the exhaust, taking a while to cool down, results in a much larger volume of light-emitting exhaust than with some other propellants. $\endgroup$
    – IronEagle
    Commented Dec 1, 2022 at 0:27


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