What Is the SI unit of power?
Spectral power distribution the incident wavelength. Mathematically, for the spectral power distribution of a radiant exitance or irradiance one may write: where "M"("λ") is the spectral irradiance (or exitance) of the light (SI units: W/m = kg·m·s); "Φ" is the radiant flux of the source (SI unit: watt, W); "A" is the area over which the radiant flux is integrated (SI unit: square meter, m); and "λ" is the wavelength (SI unit: meter, m). (Note that it is more convenient to express the wavelength of light in terms of nanometers; spectral exitance would then be expressed in units of W·m·nm.) The approximation is
SI derived unit SI derived unit SI derived units are units of measurement derived from the seven base units specified by the International System of Units (SI). They are either dimensionless or can be expressed as a product of one or more of the base units, possibly scaled by an appropriate power of exponentiation. The SI has special names for 22 of these derived units (for example, hertz, the SI unit of measurement of frequency), but the rest merely reflect their derivation: for example, the square metre (m), the SI derived unit of area; and the kilogram per cubic metre (kg/m or kg