A lux meter or lux (symbol: lx) is the SI unit of illumination. It is used in photometry. In photometry, the wavelength-weighted power emitted in a unit solid angle, in a particular direction from the light source, is called a luminous intensity. It is based on the luminosity function, which is a standardized model of the sensitivity of a human eye. Its SI unit is the candilla (cd).
The international unit system (abbreviated SI; abbreviated form of the French Le Système International d'unités), is the modern form of the metered system. It is normally made in decimal and in coefficients of ten. It is the most used system in the world in the field of science and commerce. Groups of multiple units were used in the old metric system. SI was developed in 1960 from the old meter-kilogram-second (MKS) system, rather than the centimeter-gram-second system, which had many difficulties.
The SI system does not remain stable, but continues to develop, but the units are created and changed only through international agreements. This system is almost universally applicable and most of the countries do not understand the official definitions of units other than this. But exceptions are the United States and Britain, where non-SI units still have their old systems.
The system came into force in India on April 1, 1957. Along with this, new money was introduced here, which was based on the decimal system itself. Many new naming units came into force in this system. The system consists of seven basic units (meter, kilogram, second, ampere, calvin, mole, candela, coulomb) and many other derived units. In some scientific and cultural fields, other units are also used along with the SI system. It is easy to express very small and very large quantities through SI prefixes.
The three nations have not officially accepted this system as their complete or primary measurement system. These nations are: Liberia, Myanmar and the United States.