What is the name of the machine used to measure optical density? We used it in a lab but I can't remember what they called it.

  • 2
    $\begingroup$ densitometer? turbidometer? spectrometer? spectrophotometer? There are many such devices and some details on the type of experiment may help here. $\endgroup$
    – AliceD
    Mar 4, 2015 at 4:17
  • 1
    $\begingroup$ Hmm I think it was the spectrometer. That sounds right. We where measuring the growth of cell cultures. $\endgroup$
    – Delimit04
    Mar 4, 2015 at 4:51
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    $\begingroup$ I'd bet the farm that it's a spectrophotometer. $\endgroup$
    – canadianer
    Mar 4, 2015 at 8:22

1 Answer 1


Optical Density is synonymous with absorbance which is based on the principle of absorption of light. The machine that is used to measure absorbance is called a spectrophotometer. Spectrometer does not indicate that light absorbance is being measured. A spectrometer can measure any spectrum; for e.g. Mass Spectrometer measures the spectrum of molecular mass (to be precice mass per charge).

Cell density can be also measured by the level of light scattering; turbidimeters or nephelometers are used for these kind of measurements.

PS: You should pay more attention in your class :P

  • $\begingroup$ Also called a spec, for short. $\endgroup$
    – rhill45
    Mar 6, 2015 at 1:05
  • $\begingroup$ When you use a spectrophotometer to measure culture density you are actually measuring turbidity/light scattering, not absorbance. $\endgroup$
    – Alan Boyd
    May 16, 2017 at 18:27

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