Spectroradiometer
Spectrometers discriminate the wavelength based on the position the light hits at the detector array allowing the full spectrum to be obtained with a single acquisition.
This data is also then used with built in or PC software and numerous algorithms to provide readings or Irradiance (W/cm2), Illuminance (lux or fc), Radiance (W/sr), Luminance (cd), Flux (Lumens or Watts), Chromaticity, Color Temperature, Peak and Dominant Wavelength.
Portable devices are also available for numerous spectral ranges covering UV to NIR and offer many different package styles and sizes.
Hand held systems with integrated displays typically have built in optics, and an onboard computer with pre-programmed software.
Mini spectrometers are also able to be used hand held, or in the lab as they are powered and controlled by a PC and require a USB cable.
[1] It is useful to sample the spectrum with narrow bandwidth and wavelength increments because many sources have line structures [2] Most often in spectroradiometry, spectral irradiance is the desired measurement.
Given these considerations, it is often more prudent to use a more rigorous form of the equation to account for these dependencies[3] Note that the prefix "spectral" is to be understood as an abbreviation of the phrase "spectral concentration of" which is understood and defined by the CIE as the "quotient of the radiometric quantity taken over an infinitesimal range on either side of a given wavelength, by the range".
[4] The spectral power distribution (SPD) of a source describes how much flux reaches the sensor over a particular wavelength and area.
The quality of a given spectroradiometric system is a function of its electronics, optical components, software, power supply, and calibration.
Under ideal laboratory conditions and with highly trained experts, it is possible to achieve small (a few tenths to a few percent) errors in measurements.
It generates erroneous electronic counts not related to designed spectral signal for the pixel or element of the detector array.
(In a camera photo this could appear as a large white spot, where as in a spectrometer it can appear as a dip, or cut off peak) Too short an integration time can generate noisy results (In a camera photo this would be a dark or blurry area, where as in a spectrometer this may appear are spiky or unstable readings).
Other things being equal, the Signal-to-Noise Ratio (SNR) of the collected spectra improves by the square root of the number N of scans averaged.
It is the ratio of signal counts Cs (usually at full scale) to RMS (root mean square) noise at this light level.
[8] To perform spectral analysis of a source, monochromatic light at every wavelength would be needed to create a spectrum response of the illuminant.
[9] A typical monochromator achieves this through the use of entrance and exit slits, collimating and focus optics, and a wavelength-dispersing element such as a diffraction grating or prism.
Diffraction gratings are preferable due to their versatility, low attenuation, extensive wavelength range, lower cost, and more constant dispersion.
For example, photocathodes found in photomultiplier tubes can be manufactured from certain elements to be solar-blind – sensitive to UV and non-responsive to light in the visible or IR.
They include a silicon or InGaAs based multichannel array detector capable of measuring UV, visible and near-infra light.
CMOS (Complementary Metal Oxide Semiconductor) sensors differs from a CCD in that they add an amplifier to each photodiode.
The lines of communication between monochromator, detector output, and computer should be optimized to ensure the desired metrics and features are being used.
