Question

what is the photomatry?

Answer 1

Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy in terms of absolute power. 

Answer 2

photometry is the science of measurement of light in terms of it's perceived brightness.

it is distinct from Radiometer which is the science of measurement of radiant energy.

in modern photometry ,the radiant power at each wavelength is weighed by a luminosity function that models human brightness sensitivity

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