AvaSpec spectrometers measure radiated optical energy, which can be quantified as a radiant flux, in energy per second (Watt) radiated from a source. The radiated optical energy can also be correlated with human vision (photometry), as defined in the CIE, to obtain a spectral luminous efficiency function to characterise the vision of an average human observer. 

An AvaSpec irradiance calibrated spectrometer system can measure both radiometric as well as photometric quantities. Radiometric quantities are radiant energy (in Joule), Radiant power or flux (in Watt) or irradiance (Watt per cm2). Related photometric quantities are luminous flux (lumen) or illuminance (lux or lumen per m2). 

The measured spectral distribution is used to calculate the above mentioned parameters. An intensity calibrated light source such as those in the Avantes calibration laboratory or our field calibration lamps - the AvaLight-HAL-CAL or AvaLight-DH-CAL, which have known energy output (in µWatt/cm2/nm) are used as a reference. Calibrations can be performed at Avantes calibration laboratory or in the field and stored on the EEPROM of the spectrometer (or an independent file) for future use. AvaSoft-IRRAD software is required for either type of calibration.

The colour of light parameters can be expressed by the chromaticity coordinates x, y and z. These chromaticity coordinates are obtained by taking the ratios of the tristimulus values (X, Y and Z) to their sum. The tristimulus values X, Y and Z and the spectral irradiance are computed in a wavelength range from 380nm to 780nm, using a 1nm interval. These parameters, as well as the coordinates u and v, and the colour temperature of an external light source can be calculated and displayed in realtime in the AvaSoft-IRRAD module.

The CRI colour rendering index of a light source is also included in the AvaSoft IRRAD module. The colour rendering index of a light source with a colour temperature <5000K is a measure of how close a light source matches a perfect black body radiant. In addition, AvaSoft-IRRAD features a setting for auto-adjusting the integration time during a time sequence measurement, so a large dynamic range can be achieved for applications that have both very high light level and very low light level, such as solar measurements.

AvaSoft-IRRAD enables two ways to display and save calculated output:

​

• Data can be displayed as spectral irradiance in µWatt/nm versus wavelength. Additionally, the following output parameters can be displayed - radiometric quantities µWatt/cm2, µJoule/cm2, µWatt or µJoule, photometric quantities Lux or Lumen, colour coordinates X, Y, Z, x, y, z, u, v, colour rendering index and colour temperature, and number of photons µMol/s•m2, µMol/m2, µMol/s and µMol. The AvaSoft-IRRAD module also displays raw data in Scope mode as well as the X-Y Chromaticity diagram, including parameters, which are useful for LED measurements, such as Dominant Wavelength, Purity, Central Wavelength, Peak Wavelength, Centroïd, etc.

• In Time Measurement mode, any number of functions can be displayed simultaneously against time. For each function, a different radiometric, photometric, photon or colour coordinate output parameter and/or wavelength range may be selected, as well as a different spectrometer channel.