What is the difference between a spectrophotometer and a colorimeter?

the principle of a spectrophotometer and a colorimeter is absolutely the same. both use a monochromatic light to pass thorough a substance and measures its absorbance/transmittance.

a colorimeter can only use one wavelenght at a time and have a fixed number of wavelenghts that can be used and they have to be in the visible range only.

a spectrophotometer on the other hand can not only function like a colorimeter but also take a spectrum ie the abosorbance/transmittance of a substance across the entire wave spectrum especially if it is a UV-vis or UV-vis-IR (uv visible infra red). one can also take simple absorbance in a spec including at UV or infra red wavelenghts.

now a days very few labs have colorimeters since specs are much more useful and diverse in function

YES U CAN MEASURE the optical density of your culture in a colorimete