Radiant flux Radiant flux In radiometry, radiant flux or radiant power is the radiant energy emitted, reflected, transmitted or received, per unit time, and spectral flux or spectral power is the radiant flux per unit frequency or wavelength, depending on whether the spectrum is taken as a function of frequency or of wavelength. The SI unit of radiant flux is the watt (W), that is the joule per second () in SI base units, while that of spectral flux in frequency is the watt per hertz () and that of spectral flux in wavelength is the watt per metre ()—commonly the watt
Langmuir (unit) Langmuir (unit) The langmuir (symbol: L) is a unit of exposure (or dosage) to a surface ("e.g." of a crystal) and is used in ultra-high vacuum (UHV) surface physics to study the adsorption of gases. It is a practical unit, and is not dimensionally homogeneous, and so is only used in this one field. It is named after American physicist Irving Langmuir. The langmuir is defined by multiplying the pressure of the gas by the time of exposure. One langmuir corresponds to an exposure of 10 Torr during one second. For example, exposing a surface to a gas pressure of