|MadSci Network: Physics|
Dear Chris, Interesting question. I looked back over previous MadSci responses to your question and found one by Prof. Suzanne Willis (1999): => http://www .madsci.org/posts/archives/sep99/936814333.Ph.r.html Since its been 5 years, I think its appropriate to expand the answer she gave back then. First thing to consider is the temperature of a lightning bolt. A number of source place this at 28,000-30,000 Kelvin, about 3 times the surface temperature of the Sun… => http://hypertextb ook.com/facts/1999/DavidFriedman.shtml Using this, I have plotted the Planck’s Law for “black body” radiation at ~29,000K, then applied a Wien’s Law calculation for maximum intensity. Here are those graphs (Graph Planck and Graph Wien): The first thing to note is that almost ALL of the light generated in a lightning bolt is in the far ultraviolet and “invisible” region. Very little is in the visible region. Wien’s Law indicates the maximum intensity appears at 1028 Angstroms (102.8 nm). The energy of these photons is enough to break apart oxygen and nitrogen molecules. Subsequently this light would excite, ionize, and cause the emission of their atomic and ionic species. Both oxygen and nitrogen atoms have part of their fluorescence emission spectra in the visible region. All this visible emission, taken as a whole, would appear a white or bluish-white light to the human eye. I have read that at a distance, lightning can have different shades of color… => http://wvlightning.com/faqw10.html I think this is mainly due to atmospheric effects of light refraction, scatter by dust and other atmospheric molecules, etc. Similar to how the Sun appears in different shades or hues of color at sunrise (the “green flash”) and sunset… => http://hyperphysics.phy- astr.gsu.edu/hbase/atmos/redsun.html Hope this helps answer your question! ---* Dr. Ken Beck
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