Irradiance is one of the quantities included in the field of radiometry. Basically radiometry is the measure of electromagnetic radiation through the entire spectrum, but in the most cases, the study is limited to the UV-VIS-IR region. Due to the several quantities that this field embraces there are some terms that may lead to some confusion, so is important to have in mind the main differences.

In a simple form we can say that all the quantities that radiometry describes are derived from the radiant energy, which is the term that describes the energy carried by the light and is measured in joules (J). Also, we know that light can be as simple as a monochromatic beam or a more complicated polychromatic beam. In this later case is important to know the dependence of the radiant energy with the wavelength, in such cases we talk of spectral radiant energy which is measured in J/nm. The variation of the radiant energy with time is known as the radiant flux (also called radiant power) and is measured in watts. Finally, and before detailing the irradiance, there is only missing one important quantity which describes the radiant flux per unit area and is known as radiant flux density.

Irradiance is defined as the radiant flux density incident on a surface, which is the opposite of the existence that measures the radiant flux density emitted by a surface, but both quantities have the same units, Wm-2. Spectral irradiance is an important quantity because describes the dependence of the irradiance with the wavelength and has the unity Wm-2nm-1. In some cases, mainly when dealing with sources that emit light in continuous spectra, there exists a relation between the source and the spectrum emitted by a blackbody. In these cases we talk about color temperature that is associated with the source which allows the determination of his power across the spectrum due to the Stefan-Boltzmann law.

Sarspec has available four ranges of spectrometers (detectors) that can be used for irradiance measurements. The selection of the correct spectrometer depends on the intensity, wavelength range of the light source. But there are also additional requirements one might have, such as resolution, speed, sensitivity, etc. For that we strongly advice to contact for selection of the correct configuration. Optical fibers and collimation lens are also available from Sarspec offering the possibility to collect light from basically anywhere.