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.
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 firstname.lastname@example.org 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.