How to Correct for Spectral Errors of Popular Light Sources

Apogee quantum sensors accurately quantify the amount of photosynthetic light striking a surface in units of µmol m-2 s-1. There are, however, certain factors that can introduce varying small errors into these measurements. One of these factors, spectral error, occurs when measuring a light source that has a different spectral output than the light used to calibrate the sensor. This error occurs because no quantum sensor can perfectly match the ideal quantum response, which is defined as an equal response to all wavelengths of light between 400 and 700 nm. When measuring certain light sources with our quantum sensors, an even higher level of accuracy can be achieved by applying post-measurement correction factors according to the chart below.

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 table below displays the calculated theoretical spectral errors and corresponding correction factors for many different popular 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 (CF) associated with your light source. For example, if you are using an SQ-120 under a Blue LED (448nm), which has a spectral error of -12.7 and a CF of 1.15, and you measured 115 µmol m-2 s-1, you would multiply your measurement of 115 µmol m-2 s-1 by the CF 1.15 to get 132.3 µmol m-2 s-1 (115 x 1.15 = 132.3).

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.

 

This information is also available as an interactive tool, which allows users to upload their own lighting spectrum.

Light SourceSpectral Graph
(Click to Enlarge)

Spectral Error
SQ-110
(SUN)

Correction Factor
SQ-110
(SUN)

Spectral Error
SQ-120
(ELEC)

Correction Factor
SQ-120
(ELEC)

Spectral Error
SQ-500
(Full-spectrum)

Correction Factor
SQ-500
(Full-spectrum)

Agro Ceramic Metal Halide Agro Ceramic Metal Halide Spectrum 0.0 1.00 -16.3 1.19 -1.8 1.02
Apache W LED Apache W LED Spectrum 15.8 0.86 -0.8 1.01 -0.5 1.01
Blue LED (448nm) Blue LED (448nm) Spectrum 4.2 0.96 -10.7 1.12 0.8 0.99
CF GE 45 W CF GE 45 W Spectrum 16.6 0.86 -0.5 1.01 -0.9 1.01
CF Sylvania 30 W CF Sylvania 30 W Spectrum 12.3 0.89 -3.8 1.04 0.0 1.00
CWF T5 Sylvania CWF T5 Sylvania Spectrum 16.9 0.86 0.0 N/A 0.0 N/A
Light Source Spectral Graph
(Click to Enlarge)

Spectral Error
SQ-110
(SUN)

Correction Factor
SQ-110
(SUN)

Spectral Error
SQ-120
(ELEC)

Correction Factor
SQ-120
(ELEC)

Spectral Error
SQ-500
(Full-spectrum)

Correction Factor
SQ-500
(Full-spectrum)

CWF T8 Sylvania CWF T8 Sylvania Spectrum 16.6 0.86 -0.5 1.01 0.2 1.00
CWF T12 Sylvania CWF T12 Sylvania Spectrum 15.5 0.87 -1.6 1.02 0.3 1.00
Flip Ceramic Metal Halide Flip Ceramic Metal Halide Spectrum 10.9 0.91 -14.6 1.17 -0.3 1.00
Green LED 524nm Green LED 524nm Spectrum 24.9 0.80 7.0 0.93 3.0 0.97
High Pressure Sodium High Pressure Sodium Spectrum 17.7 0.85 0.5 1.00 0.0 1.00
Illumitex RB LED Illumitex RB LED Spectrum -36.0 1.56 -45.2 1.82 -2.6 1.03
Light Source Spectral Graph
(Click to Enlarge)

Spectral Error
SQ-110
(SUN)

Correction Factor
SQ-110
(SUN)

Spectral Error
SQ-120
(ELEC)

Correction Factor
SQ-120
(ELEC)

Spectral Error
SQ-500
(Full-spectrum)

Correction Factor
SQ-500
(Full-spectrum)

Incandescent 40 W Incandescent 40 W Spectrum -15.8 1.19 -28.5 1.40 -7.3 1.08
Incandescent 100 W Incandescent 100 W Spectrum -17.0 1.20 -29.5 1.42 -7.6 1.08
Kessil Tuna Blue Kessil Tuna Blue Spectrum 11.9 0.89 -4.7 1.05 1.7 0.98
LI 1800-02 Calibrator LI 1800-02 Calibrator Spectrum -10.6 1.12 -24.1 1.32 -5.7 1.06
Lighting Science RB LED Lighting Science RB LED Spectrum -48.4 1.94 -55.8 2.26 -3.4 1.04
Lighting Science RW LED Lighting Science RW LED Spectrum -43.4 1.77 -51.5 2.06 -3.0 1.03
Light Source Spectral Graph
(Click to Enlarge)

Spectral Error
SQ-110
(SUN)

Correction Factor
SQ-110
(SUN)

Spectral Error
SQ-120
(ELEC)

Correction Factor
SQ-120
(ELEC)

Spectral Error
SQ-500
(Full-spectrum)

Correction Factor
SQ-500
(Full-spectrum)

Metal Halide Metal Halide Spectrum 13.2 0.88 -4.3 1.04 -5.7 1.06
Quartz Halogen Quartz Halogen Spectrum -10.5 1.12 -24.0 1.32 -5.7 1.06
RB LED RB LED Spectrum 19.3 0.84 2.2 0.98 -1.5 1.02
Red LED 635 nm RED LED 635nm Spectrum 21.7 0.82 -4.4 1.05 -2.0 1.02
Reflected Conifer Reflected Conifer Spectrum 5.5 0.95 -11.3 1.13 -2.2 1.02
Reflected Deciduous Reflected Deciduous Spectrum 4.9 0.95 -11.9 1.14 -2.0 1.02
Light Source Spectral Graph
(Click to Enlarge)

Spectral Error
SQ-110
(SUN)

Correction Factor
SQ-110
(SUN)

Spectral Error
SQ-120
(ELEC)

Correction Factor
SQ-120
(ELEC)

Spectral Error
SQ-500
(Full-spectrum)

Correction Factor
SQ-500
(Full-spectrum)

Reflected Grass Reflected Grass Spectrum 5.7 0.95 -10.9 1.12 -2.2 1.02
RGB LED RGB LED Spectrum 20.3 0.83 3.0 0.97 -0.8 1.01
Sun Clear Sun Clear Spectrum 0.0 N/A -14.8 1.17 -2.2 1.02
Sun Cloudy Sun Cloudy Spectrum 1.4 0.99 -14.4 1.17 -1.7 1.02
Under Alfalfa Canopy Under Alfalfa Canopy Spectrum 6.4 0.94 -11.9 1.14 -1.7 1.02
Under Maple Canopy Under Maple Canopy Spectrum 6.8 0.94 -11.8 1.13 -0.9 1.01
Light Source Spectral Graph
(Click to Enlarge)

Spectral Error
SQ-110
(SUN)

Correction Factor
SQ-110
(SUN)

Spectral Error
SQ-120
(ELEC)

Correction Factor
SQ-120
(ELEC)

Spectral Error
SQ-500
(Full-spectrum)

Correction Factor
SQ-500
(Full-spectrum)

Under Pine Canopy Under Pine Canopy Spectrum 5.3 0.95 -12.9 1.15 -0.4 1.00
Under Wheat Canopy Under Wheat Canopy Spectrum 6.4 0.94 -11.7 1.15 -1.1 1.01
Valoya RW LED Valoya RW LED Spectrum -16.0 1.19 -28.0 1.39 -6.0 1.06
WWF LED WWF LED Spectrum 6.0 0.94 -9.2 1.10 -1.9 1.02
2 Actinic, 2 Blue Plus 2 Actinic 2 Blue Plus Spectrum -2.3 1.02 -16.8 1.20 -3.0 1.03
3 T5, 1 Actinic 3 T5 1 Actinic Spectrum 9.2 0.92 -7.0 1.08 -2.0 1.02
4 Actinic 4 Actinic Spectrum -16.0 1.19 -28.5 1.40 -10.0 1.11
4 Blue Plus 4 Blue Plus Spectrum 7.4 0.93 -8.5 1.09 -3.0 1.03