You are here:   HomeSupportFAQsGeneralIn many scientific papers we’ve seen the units of the readings in W/m2. Is this the same unit as the one the software uses (i.e., W/m2/nm)? Do we need to do some calculations to obtain W/m2?

In many scientific papers we’ve seen the units of the readings in W/m2. Is this the same unit as the one the software uses (i.e., W/m2/nm)? Do we need to do some calculations to obtain W/m2?

The units of W/m2 and W/(m2 nm) differ because the first measure does not specify the wavelength, meaning simply that a certain amount of radiative power per surface area was measured. When "nm" is included, the measurement is the "radiative power per surface area and per wavelength interval."

In a more formal sense, "irradiance,"  "spectral irradiance," and the associated units are defined as follows:

Irradiance E, is the radiant energy dQ, arriving per time interval dt, and per area dA, on a surface. The associated SI unit is W/m2. Spectral irradiance Eλ, is the radiant energy dQ, arriving per time interval dt, per area dA, and per wavelength interval dλ, on a surface. The associated unit is W/(m2 nm). 