Define about the Photometry - colorimetry?

Photometry is the measurement of the luminous intensity light or the amount of luminous light falling on a surface from such a source. The term photometric measurement was defined originally as the process used to measure light intensity independent of wavelength. Modern instruments, however, isolate a narrow wavelength range of the spectrum for measurements.

The instruments that use filters for this purpose are referred to as filter photometers, whereas, those that use prisms or gratings are called spectrophotometers. A simple spectrophotometer called a colorimeter is used to measure the amount of light a sample absorbs. The primary analytical utility of filter photometry or spectrophotometry is the isolation and use of discrete portions of the spectrum for purposes of measurement.