Apogee quantum sensors measure the quantity of light striking a surface in units of µmol m-2 s-1. There are many potential sources of errors that can reduce the accuracy of light measurements. One of these errors, spectral error, occurs when measuring a light source that has a different spectral output than the spectral output of the light source used to calibrate the sensor. The error occurs because no quantum sensor perfectly matches the ideal quantum response, which is defined as an equal response to all wavelengths of light between 400 and 700 nm.
Spectral errors can be approximated using wavelength dependent calculations that account for the spectral response of the quantum sensor, the spectral output of calibration light source, and the spectral output of light source being measured. The interactive tool below calculates the theoretical spectral errors and corresponding correction factors for many different lights sources. The spectral errors are calculated relative to each sensor's calibration source (the SQ-110 is calibrated to clear-sky sunlight, the SQ-120 and SQ-500 are calibrated to 4100K cool white fluorescent T5 lamps).
To correct for spectral error multiply your measured value by the correction factor associated with your light source. For example, if you are using an SQ-120 under clear-sky sunlight, the expected spectral error is -13.9% and the correction factor is 1.16. Assuming you measured 1150 µmol m-2 s-1, you would multiply your measurement of 1150 µmol m-2 s-1 by the correction factor 1.16 to get 1334 µmol m-2 s-1 (1150 x 1.16 = 1334).
SQ-110 correction factors apply to sun calibrated models SQ-110, 212, 214, and 215, and models SQ-420, MQ-100, 200, and 210 when in SUN setting.
SQ-120 correction factors apply to electric calibrated models SQ-120, 222, 224, and 225, and models SQ-420, MQ-100, 200, and 210 when in ELEC setting.
SQ-500 correction factors apply to models SQ-500 and 520, and MQ-500, 501, and 510.
You can also upload your own lighting spectrum to get the most accurate correction factors to apply. See the video below or the 'User Guide' tab of the tool for more information.