fotometers

Fotometers, also spelled photometers in many contexts, are instruments that measure light intensity or luminous flux, either from a light source or as light interacts with a sample. In photometric use, measurements are weighted by the human eye’s response and are reported in units such as lumens, lux, or candela, reflecting perceived brightness rather than raw radiometric power.

Most photometers combine a light source, an optical path or sample holder, and a detector such as a photodiode, photomultiplier tube, or photoresistor. Many modern instruments include spectral selection through filters or a monochromator to measure at a specific wavelength. In chemical and biological work, photometers are used as part of spectrophotometric methods to measure absorbance or transmittance of solutions; by Beer-Lambert law, absorbance relates to concentration.

Photometers can be categorized by how they sample light: transmission photometers measure light that passes through a sample, while reflectance photometers measure light reflected from a surface. In photography, light meters estimate scene luminance to guide exposure, with incident meters measuring light falling on the subject and reflected meters measuring light reflected from the scene.

Applications span laboratory assays (colorimetric tests, enzyme activity, and nucleic acid quantification), environmental monitoring and water quality, food and beverage analysis, and industrial process control. Portable field models enable quick measurements, while benchtop units offer higher sensitivity and broader spectral capabilities.

Calibration and accuracy depend on traceable standards, regular checks of light sources, and detector linearity to minimize stray light and ensure repeatable results. Photometers are valued for their versatility in measuring optical properties across science, industry, and photography.