Spectroradiometry and photometry - the entire light spectrum

Instrument Systems supplies technically refined test & measurement systems to meet all requirements in spectroradiometry and photometry, e.g. measurements of the solar spectrum, from a solar simulator or at an energy-saving lamp. These measurement systems are calibrated using standards that are based on PTB (Germany) or NIST (USA) reference standards.

Radiometric quantities describe the physical radiation properties over the entire spectrum from UV to infrared, while photometric quantities relate to the effect on the human eye and are therefore restricted to the visible range from 380 to 780 nm. Spectroradiometry relates to spectral measurements of radiometric quantities.

The following table gives an overview of the different optical quantities with sample applications: 

Measurement
at
Test & measurement accessories Radiometric unit Photometric unit
Energy-saving lamp ISP Integrating Sphere

Radiant power [W] 

Luminous flux
[lm]

LEDLED Adapter 

Radiant intensity
[W/sr]

Luminous intensity
[lm/sr = cd]

Sun EOP External Optical Probe 

Irradiance
[W/m²]

Illuminance
[lm/m² = lux]

DisplayTOP Telescopic Optical Probe 

Radiance
[W/sr m²]

Luminance
[cd/m²]

Spectoradiometry and photometry place extremely high requirements on the spectrometer, if accurate measurement results are to be attained. The high-quality and precise spectrometers from Instrument Systems have been specially designed for these applications. The appropriate measurement accessories are also supplied for the relevant radiometric and photometric quantities. Accessories are connected to the spectrometer by an innovative fiberoptic adapter. This feature maintains absolute calibration even if accessories are changed.

Miniature spectrometers with low-cost front-Illuminated CCD line sensors do not meet the specified requirements because their dynamic range and stability are not adequate for accurate absolute calibrations.

Spectroradiometry

Instrument Systems recommends the following spectrometers for precise spectroradiometric measurements:

  • The CAS 140CT Array Spectrometer is ideal for taking measurements at flash lamps and solar simulators. Different models cover the spectral range from 200 to 2150 nm.
  • The Spectro 320 scanning spectrometer is supplied as a single or double monochromator and is ideal for applications that require a large dynamic range and very low stray light (e.g. UV-B measurements). This spectrometer also allows a broad spectral range from 190 to 5000 nm to be analyzed in a single scan.

Photometry

Photometric measurements are restricted to the visible spectrum of 380 to 780 nm (360 to 830 nm in extended range). Photometric and colorimetric quantities can also be calculated from spectral data but the reverse calculation is not possible. Spectroradiometers rather than conventional photometers are therefore generally used to obtain accurate photometric measurements. Photometers also require a correction for the spectral mismatch.

The following spectrometers from Instrument Systems are recommended for photometric measurements:

  • The CAS 140CT Array Spectrometer as a precision measuring instrument to meet all requirements in R&D and production
  • The MAS 40 CCD Array Spectrometer as a low-cost entry-level instrument for laboratory settings and quality control