The basic purpose of a photometer is to measure light. Since light comes in all different forms, many different types of photometers exist. Photometry has been around for many years, though photometers have come a long way from their humble beginnings.
The first type of photometer wasn't an instrument at all. In fact, before photometers were invented measuring light was only possible by using the naked human eye. As time progressed, actual photometers came into existence, and today photometers can be used to measure all kinds of light ranging from fluorescence to light absorption.
The most common use of photometers today is within the field of digital photography. When used in photography, the main task of a photometer is to determine the right amount of exposure. Since light is never even, obtaining an ideal photograph means taking light into account. Photometers that are built into digital cameras measure the amount of light within an area in order to produce the best possible photograph. While photometers are widely used within the field of photography, there are other uses for photometers as well.
In astronomy, a photometer is used to measure the amount of light contained within stars or other celestial points. In addition, some photometers can accurately measure sunlight as it falls onto the earth. These instruments can also be used in industrial settings such as the paint industry. For example, within the paint industry, photometers are often used to determine the actual color of an area accurately.
Photometers can also be used to measure the intensity of a flame, and they can be used to measure infrared light. In almost any instance that light needs to be recorded or measured, a photometer is often the instrument of choice. Choosing the right type of instrument for the task at hand requires a basic understanding of the type of light that is meant to be measured.
Photometers can measure illuminance, irradiance, light absorption, scattering, reflection of light, fluorescence, phosphorescence, and luminescence. Determining the kind of light that is to be measured is the first step towards selecting the right instrument. To detect light, photometers use photoresistors, photodiodes, or photomultipliers. In order to accurately measure light, the light must first pass through a filter. Once the light has been filtered, it can then be measured in wavelengths.
Some photometers measure light in photons, rather than measuring light through a constant light stream. The main difference between an instrument that measures light through photos and one that measures light through flux is the actual read-out of the light analysis. A photon photometer will produce results in photon units.