Photometers produce electrical signals that correspond to radiant flux energy for a series of discrete wavelength intervals. They are used to measure wavelengths of light spectra and optical or atomic emissions. Photometry is the study of light from a radiant light source such as the sun, laser, or lamp. Radiation is separated into component wavebands in order to measure each individual band. These radiance measurements are expressed in different ways, depending on how radiation is collected and processed. Typically, wavelengths are measured in nanometers (nm).
Performance criteria for photometers include spectral range and resolution. Spectral range is the range of wavelengths that a photometer can measure. Resolution is the smallest wavelength that a photometer can distinguish. Operating temperature and operating humidity are additional parameters to consider when selecting photometers.
Photometers have four basic components:
- the input unit
- the monochromator
- the detector
- the control system
The input unit gathers radiation and delivers it to the monochromator. The monochromator separates the radiation into individual wavebands. The detector measures the radiation of each band. The control system defines and stores the data. When radiant energy is broken into its monochromatic components for measurement, the energy becomes a function of wavelength. The designations for the resulting quantities are called spectral irradiance. IR photometers are used to measure the wavelength of infrared (IR) light. UV photometers are used to measure the wavelength of ultraviolet (UV) light. There are three main UV bands: UVA, UVB, and UVC. UVA is the near or long-wave UV band (~315–400 nm). UVB is the middle UV band (~280–315 nm). UVC is used with ultraviolet germicidal irradiation (UVGI) to inactivate pathogens by destroying their DNA and RNA.
Photometers are used in many medical, laboratory, and industrial applications. Uses include the identification and quantification of chemical components, pharmaceutical quality control, and astronomical calculations. Some photometers are portable or include application software. Others are designed for demanding industrial environments and can be used in high-temperature or high-humidity conditions. Photometers that are destined for the European market bear the CE mark to indicate compliance with applicable European Union (EU) directives such as Restriction of Hazardous Substances (RoHS) and Waste Electrical and Electronic Equipment (WEEE).
Thomas Wydra / CC BY-SA 3.0