Measurement of Optical Density

hochbeam at hochbeam at
Wed Feb 15 08:19:57 EST 1995

For particles of the size, shape, and refractive index of bacteria,
light scattering is much greater for red light.  (viz. van de
Hulst, Light Scattering by Small Particles).  So red gives
a bigger signal in the spectrophotometer, therefore more
sensitivity.  Why not go past 600?  Sensitivity of some spec
detectors drops off, and the light gets hard to see past
670 or so.  But it's a round number, not a constant of nature.
If someone way back had chosen 610, the foundations of science
would not collapse.

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