The technical definition of a NIT is as follows:
NIT: The candela per square metre (cd/m2) is the derived International
System unit (SI) of luminance. The unit is based on the candela, the SI unit of luminous intensity,and the square meter, the SI unit of area. Nit is a deprecated non-SI name also used for this unit (1 nit = 1 cd/m2).Technically, a NIT measures ‘luminance’. It is the absolute measurement of light from a light source.
Most manufacturers list their maximum light outputs for various pitches on spec sheets in NITs.Interestingly, NITs are not optimal as a regulatory guideline. If you are a jurisdiction implementing brightness guidelines on LED displays, please reference these links below.